The tremendous diversity of Labiobaetis Novikova & Kluge in Indonesia (Ephemeroptera, Baetidae)

Abstract Material collected between 2010 and 2014 on the Indonesian islands of Sumatra, Bali, Sumba, Sumbawa, Sulawesi, and Seram unveiled the enormous diversity of Labiobaetis Novikova & Kluge in this country. Five species were reported from Indonesia previously (L. fulmeki (Ulmer), L. obscurum (Ulmer), L. necopinatum (Müller-Liebenau), L. ulmeri (Müller-Liebenau), and L. boettgeri (Ulmer)); all were described from adults only and no species were previously known at larval stage. We identified 18 new species by integrative taxonomy using genetic distance (COI, Kimura-2-parameter) and morphology, and they are described and illustrated based on their larvae. Another species, L. multus (Müller-Liebenau) from Malaysia, was also found in Indonesia, increasing the total number of species in Indonesia to 24. Seven morpho-groups of species are proposed based on morphological characters and a key to the larvae of all species from Indonesia and adjacent countries is provided. The total number of Labiobaetis species worldwide is augmented to 123. The examination of the new species allowed us to slightly modify the generic attributes of the larvae. The interspecific K2P distances are usually between 11% and 24%, the intraspecific distances are usually between 0% and 3%. The remarkable richness of the genus in Indonesia is discussed.


Introduction
The family Baetidae has the highest species diversity among mayflies, comprising 1,070 species in 110 genera Brittain 2015, Jacobus et al. 2019), which is approximately one quarter of all mayfly species worldwide (Gattolliat andNieto 2009, Jacobus et al. 2019). They have a cosmopolitan distribution with the exception of Antarctica and New Zealand. Investigations of the molecular phylogeny of the Order Ephemeroptera revealed the relatively primitive status of the family (Ogden andWhiting 2005, Ogden et al. 2009). The genus Labiobaetis Novikova & Kluge, 1987 is one of the richest genera of Baetidae with 105 previously described species (Barber-James et al. 2013, Webb 2013, Shi and Tong 2014, Kubendran et al. 2014. The distribution of Labiobaetis is nearly worldwide, with the exception of the Neotropical realm and New Caledonia; it is widely diversified in the Afrotropical (28 species) and Oriental realms (23 species) as well as in New Guinea (32 species) (Lugo-Ortiz et al. 1999, Gattolliat and Nieto 2009. The status and validity of the genus has long been a subject of controversy, but today Labiobaetis is widely accepted as a valid genus (Lugo-Ortiz and McCafferty 1997, Lugo-Ortiz et al. 1999, Gattolliat 2001, Fujitani et al. 2003, Fujitani 2008, McCafferty et al. 2010, Gattolliat and Staniczek 2011, Kluge and Novikova 2011, Kluge 2012, Webb 2013, Kubendran et al. 2014, Shi and Tong 2014. The history and concept of the genus Labiobaetis were recently summarized in detail (Shi andTong 2014, Kaltenbach and. All Oriental species previously transferred to Pseudocloeon (Lugo-Ortiz et al. 1999) were formerly reassigned to Labiobaetis by Shi and Tong (2014). Molecular reconstructions indicated that the concept of Labiobaetis is probably at least diphyletic (Monaghan et al. 2005, Gattolliat et al. 2008. Indonesia is an immense archipelago of more than 18,000 islands extending more than 5,000 km, from 95°E to 141°E and from 6°N to 11°S. It is one of the most biologically rich countries in the world. The high levels of species richness and endemism are mainly attributable to a complex geological history that brought together two different biological realms (Oriental realm and Australasian realm), separated by a transitional region (Wallacea) (Kingston 2010, Hall 2010. The main islands are Sumatra, Java, Borneo (partly, Kalimantan Province), Sulawesi, and New Guinea (partly, provinces West Papua and Papua). Furthermore, there are big island groups like the Lesser Sunda Islands, the Moluccas, and the Banda Islands.
The diversity of Labiobaetis in Indonesia was poorly known. Five species were reported from Indonesia (L. fulmeki (Ulmer), L. obscurum (Ulmer), L. necopinatum (Müller-Liebenau), L. ulmeri (Müller-Liebenau), and L. boettgeri (Ulmer)). All were described from adults only and no species were known at the larval stage (Ulmer 1913, 1924, 1939, Müller-Liebenau 1981. The generic attribution of these species is still controversial as Labiobaetis remains difficult to delimit at the imaginal stage. Here, we describe 18 new species of Labiobaetis based on larvae collected at different locations in Indonesia (Sumatra,Bali,Sumba,Sumbawa,Sulawesi,Seram;Fig. 53a) between 2010 and 2014; adults were not collected. We also report another species already known from Malaysia (L. multus (Müller-Liebenau)). Thereby, we consider Labiobaetis sensu lato, even if we presume that the genus is probably polyphyletic. We are currently still missing morphological characters and especially genetic evidence to split the genus into monophyletic lineages. Genetic studies on species from all realms involving nuclear genes are necessary to unveil the generic delimitation of Labiobaetis at a later point in time.
Material from the island of Borneo, including the Indonesian province Kalimantan as well as Brunei and the Malaysian province Sabah, will be treated in a separate paper (Kaltenbach and Gattolliat in press); material from the Papua Province of Indonesia was already treated in a recent paper .

Materials and methods
The specimens were mainly collected by Michael Balke (Zoologische Staatssammlung München, ZSM, Germany). Further material was collected by Jean-Marc Elouard (France) and Morgan Gueuning (University of Neuchâtel, Switzerland; Gueuning et al. 2017). The specimens were preserved in 70%-96% ethanol. The dissection of larvae was done in Cellosolve  with subsequent mounting on slides with Euparal liquid, using an Olympus SZX7 stereomicroscope.
The DNA of part of the specimens was extracted using non-destructive methods allowing subsequent morphological analysis (see Vuataz et al. 2011 for details). We amplified a 658 bp fragment of the mitochondrial gene cytochrome oxidase subunit 1 (COI) using the primers LCO 1490 (GGTCAACAAATCATAAAGATATTGG) and HCO 2198 (TAAACTTCAGGGTGACCAAAAAATCA) (Folmer et al. 1994). The polymerase chain reaction was conducted with an initial denaturation temperature of 98 °C for 30 sec followed by a total of 37 cycles with denaturation temperature of 98 °C for 10 sec, an annealing temperature of 50 °C for 30 sec and an extension at 72 °C for 30 sec, final extension at 72 °C for 2 min. Sequencing was done with Sanger's method (Sanger et al. 1977). The genetic variability between specimens was estimated using Kimura-2-parameter distances (K2P, Kimura 1980), calculated with the program MEGA 7 (Kumar et al. 2016, http://www.megasoftware.net). The GenBank accession numbers are given in Table 1, nomenclature of gene sequences is according to Chakrabarty et al. (2013). The distribution map was generated with the program QGIS (http://qgis.org), the program GEOLocate (http://www.museum.tulane.edu/geolocate/web/WebGeoref. aspx) and Google Earth (http://www.google.com/earth/download/ge/) were used to attribute approximate GPS coordinates to sample locations of Müller-Liebenau (1982, 1984a and Soldan (1991).
The taxonomic descriptions and the key presented herein were generated with a DELTA (Dallwitz 1980, Dallwitz et al. 1999, Coleman et al. 2010) database containing the morphological states of characters of the Labiobaetis species of Indonesia and Southeast Asia.
The new species described in this study were all compared to paratypes (on slides) of the species already known from Southeast Asia (excluding Southern China; deposited in Zoologische Staatssammlung München, ZSM).
For the terminology we are referring to Hubbard (1995) and to Morihara and Mc-Cafferty (1979). The postero-lateral extension of the paraproct is termed cercotractor following Kluge (2004).

New species descriptions
Abbreviations: Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of 1 + 4 long, simple setae; B) labial palp segment II with a broad, thumb-like distomedial protuberance, segment III conical; C) fore femur rather broad, length ca. 3× maximum width, dorsal margin with a row of ca. nine curved, spine- ; d-f distolateral process at scape of antenna, d absent e poorly developed f well developed; g-j labial palp, distomedial protuberance of segment II, g lobed h thumb-like i slender thumb-like j hook-like; k-n labial palp, shape of segment III, k oblong, distally with small projection l slightly pentagonal, distally slightly pointed m approx. semicircular n conical, distally slightly truncate; o-q distolateral excavation at maxillary palp segment II, o well developed p poorly developed q absent; r-u hypopharynx, medial tuft of stout setae, r well developed, long s well developed, average length t well developed, short u poorly developed; v-y hindwing pads, v absent w minute x small y well developed; z1, z2 paraproct, z1 distally not expanded z2 distally expanded. like setae; D) fore claw with 9-12 denticles; E) paraproct distally not expanded, with 11-18 stout marginal spines.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright, median, dorsal suture, thorax and abdomen with pattern as in Fig. 47a, forewing pads with brown striation. Head, thorax, and abdomen ventrally light brown, legs transparent, femur with a distomedial brown spot and apex brown, tibia and tarsus distally brown (Fig. 52a). Caudal filaments light brown with a dark brown band at ca. 1/2 of cerci.
Antenna with scape and pedicel subcylindrical, with well-developed distolateral process at scape (Fig. 3f ); flagellum with broad, lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 2a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with long, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 4 long, simple setae, the first two setae after the central seta are closely together. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with five short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 2b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex. Tuft of setae at apex of mola present.
Left mandible (Fig. 2d, e). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola slightly convex, with minute denticles toward subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola absent.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 2g). Galea-lacinia with one simple, robust apical seta under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and 4-5 long, simple setae. Maxillary palp 1.3× as long as length of galea-lacinia; two segmented; palp segment II 1.2× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with slight excavation at inner distolateral margin.
Labium (Fig. 2h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with 8-9 spine-like setae, distalmost seta much longer than other setae; apex with two long, robust, pectinate setae and one medium, robust seta; outer margin with 5-6 spine-like setae increasing in length distally; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in anteromedial area; dorsally with a row of four long, spine-like setae near inner margin. Labial palp with segment I 0.9× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.5× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of 4-5 long, spine-like, simple setae near outer margin. Segment III conical; apex rounded; length 1.0× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent (Fig. 3g). Foreleg (Fig. 3a, b). Ratio of foreleg segments 1.4:1.0:0.6:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. nine curved, spine-like setae; length of setae 0.13× maximum width of femur. Apex rounded; with one pair of spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of short, spine-like setae and fine, simple setae, near margin some stout, apically rounded setae; on apex one longer, spine-like, apically rounded seta. Ventral margin with a row of curved, spine-like setae, on apex some spine-like, partly bipectinate setae and a tuft of long, fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, stout setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 9-12 denticles; distally pointed; with 5-7 stripes; subapical setae absent.
Tergum (Fig. 3c). Surface with irregular rows of U-shaped scale bases and scattered micropores. Posterior margin of tergum IV with triangular spines, wider than long. Gills (Fig.3d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I ca. 2/3 length of segment II. Gill IV as long as length of segments V and 2/3 VI combined. Gill VII as long as length of segments VIII and 1/3 IX combined.
Etymology. Dedicated to the indigenous Batak people from Sumatra. Distribution. Indonesia: Sumatra. Biological aspects. The specimens were collected at altitudes from sea level to 280 m.
Labium (Fig. 4h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae; outer margin with six spine-like setae; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa subrectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in anteromedial area; dorsally with a row of four long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I with fine, simple setae along margins. Segment II with elongated, thumb-like distomedial protuberance; distomedial protuberance 0.7× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of five long, spine-like, simple setae near outer margin. Segment III conical; apex slightly pointed; length 1.1× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent (Fig. 5g). Foreleg (Fig. 5a, b). Ratio of foreleg segments 1.2:1.0:0.6:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. ten curved, spine-like setae; length of setae 0.16× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of curved, spine-like setae; on apex one longer, spine-like, apically rounded seta. Ventral margin with a row of curved, spine-like setae, on apex several spine-like, bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 2/3. Tarsus. Dorsal margin with a row of short, curved, spine-like setae, on apex fine, simple setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 12-13 denticles; distally pointed; with 4-5 stripes; subapical setae absent.
Tergum (Fig. 5c). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergum IV with triangular spines, medially longer than wide, laterally shorter and approx. as long as wide.
Gills (Fig. 5d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I ca. 1/2 length of segment II. Gill IV as long as length of segments V and 2/3 VI combined. Gill VII little longer than length of segment VIII.
Etymology. Refers to the island Sulawesi, where the specimens were collected. Distribution. Indonesia: Sulawesi. Biological aspects. The specimens were collected at an altitude of 660 m.   and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and four long, simple setae. Maxillary palp 1.3× as long as length of galea-lacinia; two segmented; palp segment II 1.2× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with slight excavation at inner distolateral margin. Labium (Fig. 6h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight spine-like setae, distalmost seta much longer than other setae; apex with two long and one medium, robust, pectinate setae; outer margin with six spine-like setae; ventral surface with short, fine, simple setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in anteromedial area; dorsally with a row of five long, spine-like setae near inner margin. Labial palp with segment I approx. as long as length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with large, lobed distomedial protuberance; distomedial protuberance 0.7× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of five long, spine-like, simple setae near outer margin. Segment III oblong; apex rounded; length 1.1× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 7a, b). Ratio of foreleg segments 1.2:1.0:0.6:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. ten curved, spine-like setae; length of setae 0.16× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch reduced to a few setae. Tibia. Dorsal margin with a row of short, stout setae and fine, simple setae; on apex one longer, spine-like, apically rounded seta. Ventral margin with a row of curved, spine-like setae, on apex several spine-like, partly bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, stout setae and fine, simple setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 12-14 denticles; distally pointed; with five stripes; subapical setae absent.
Tergum (Fig. 7c). Surface with irregular rows of U-shaped scale bases and micropores. Posterior margin of tergum IV with triangular spines, approx. as long as wide.
Gills (Fig. 7d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I ca. 3/4 length of segment II. Gill IV as long as length of segments V and VI combined. Gill VII as long as length of segments VIII and 1/2 IX combined.

Labiobaetis difficilis group of species
With the following combination of characters: A) dorsal surface of labrum with submarginal arc of feathered setae; B) labial palp segment II with large, thumb-like distomedial protuberance; C) seven pairs of gills; D) paraproct not expanded distally; E) hindwing pads absent.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture, thorax and abdomen with bright pattern as in Fig. 47d, forewing pads with bright striation. Head, thorax, and abdomen ventrally brown, legs transparent, femur ventrodistomedially and distally with brown spot and dorsally with brown streak along margin (Fig. 52c), caudal filaments transparent with brown band at 1/3 of cerci.
Antenna with scape and pedicel subcylindrical, with well-developed distolateral process at scape; flagellum with broad, apically blunt spines and fine, simple setae on apex of each segment.
Labrum (Fig. 9a). Rectangular, length 0.8× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 8-9 feathered setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with four short, spinelike setae near lateral and anterolateral margin.
Right mandible (Fig. 9b, c). Incisors fused. Outer and inner sets of denticles with 4 + 4 denticles. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex. Tuft of setae at apex of mola present.
Left mandible (Fig. 9d, e). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola slightly convex. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae and slightly lanceolate setae scattered over surface.
Maxilla (Fig. 9g). Galea-lacinia with one simple, robust apical seta under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid, and pectinate. Medially with one bipectinate, spine-like seta and five long, simple setae. Maxillary palp approx. as long as length of galea-lacinia; two segmented; palp segment II 1.6× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment slightly pointed, with excavation at inner distolateral margin. Labium (Fig. 9h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with nine spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae; outer margin with seven spine-like setae increasing in length distally; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and 2-3 medium, simple setae in anteromedial area; dorsally with a row of four long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.5× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of four long, spine-like, simple setae near outer margin. Segment III conical; apex slightly pointed; length 0.8× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg ( Fig. 10a-f ). Ratio of foreleg segments 1.3:1.0:0.6:0.2. Femur. Length ca. 4× maximum width. Dorsal margin with a row of ca. 15 curved, spine-like setae, apically rounded and with minute serration, and many fine, simple setae; length of setae 0.17× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae, apically rounded and with minute serration, and some short, stout setae. Short, stout, lanceolate setae scattered along the ventral margin; femoral patch reduced to a few setae. Tibia. Dorsal margin with a row of short, lanceolate, apically rounded setae and many short, lanceolate, apically rounded setae scattered along the dorsal margin. Ventral margin with a row of short, curved, spine-like setae, on apex some spine-like, partly bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, lanceolate, apically rounded setae and many short, lanceolate, apically rounded setae scattered along the dorsal margin. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 15 denticles; distally pointed; with 7-8 stripes; subapical setae absent.
Tergum (Fig. 10g). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae and micropores. Posterior margin of tergum IV with rounded or triangular spines, wider than long. Gills (Fig. 10h). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae partly extending from main trunk towards outer and inner margins. Gill I ca. 2/3 length of segment II. Gill IV as long as length of segments V and 2/3 VI combined. Gill VII as long as length of segments VIII and 1/3 IX combined.
Etymology. Dedicated to Jean-Marc Elouard, the collector of the specimens and well-known ephemerologist. The name is an anagram of Elouard.
Distribution. Indonesia: Sumatra. Biological aspects. The specimens were collected at an altitude of 530 m.  Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of 1 + 7 long, feathered setae; B) labial palp segment II with broad thumb-like distomedial protuberance; C) fore femur rather broad, length 3.3× maximum width, dorsal margin with a row of ca. 13 spine-like setae and some spinelike setae scattered along margin, D) spines at posterior margin of tergum IV triangular, longer than wide; E) paraproct distally not expanded, with 26-32 stout marginal spines.
Description. Larva (Figs 11,12,48a,52d). Body length 8.2 mm. Colouration. Head, thorax, and abdomen dorsally dark brown, head and thorax with bright median, dorsal suture, thorax and abdomen with bright pattern as in Fig.  48a, forewing pads light brown with darker striation. Head, thorax and abdominal segment I ventrally transparent, abdominal segments II-X ventrally brown, femur transparent, with a ventroproxomedial and dorsodistomedial brown streak and an apical brown spot, tibia and tarsus light brown (Fig. 52d), caudal filaments light brown, with a dark brown band at 1/3 of cerci.
Antenna with scape and pedicel subcylindrical, with poorly developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 11a, b). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 7 long, feathered setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with four short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 11c, d). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex. Tuft of setae at apex of mola present.
Left mandible (Fig. 11e, f ). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Hypopharynx (Fig. 11g). Lingua longer than superlingua. Lingua approx. as broad as long; medial tuft of stout setae poorly developed; distal half not expanded. Superlingua rounded; lateral margin rounded; fine, long, simple setae along distal margin. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and four long, simple setae. Maxillary palp 1.4× as long as length of galea-lacinia; two segmented; palp segment II 1.3× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment constricted, with excavation at inner distolateral margin.
Labium (Fig.11i, j). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with ten spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with six long spine-like setae increasing in length distally; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in anteromedial area; dorsally with a row of six long, spine-like setae near inner margin. Labial palp with segment I 0.9× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.7× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of five medium, spine-like, simple setae near outer margin. Segment III conical; apex slightly pointed; length 1.1× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 12a, b). Ratio of foreleg segments 1.3:1.0:0.6:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. 13 spine-like setae and some spine-like setae scattered along margin; length of setae 0.18× maximum width of femur. Apex rounded; with one pair of spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of short, curved, spine-like setae; on apex one longer, curved, spine-like seta. Ventral margin with a row of curved, spine-like setae, on apex with several stout, partly bipectinate, spine-like setae and a tuft of long, fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, spine-like setae and fine, simple setae. Ventral margin with a row of curved, spinelike setae. Tarsal claw with one row of 11-13 denticles; distally pointed; with six stripes; subapical setae absent.
Tergum (Fig. 12c). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae and micropores. Posterior margin of tergum IV with triangular spines, longer than wide. Gills (Fig. 12d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I a little longer than segment II. Gill IV as long as length of segments V and 3/4 VI combined. Gill VII as long as length of segments VIII and 1/2 IX combined.

Labiobaetis sumigarensis group of species
With the following combination of characters: A) dorsal surface of labrum with submarginal arc of clavate, apically smooth setae; B) labial palp segment II with large, lobed or thumb-like distomedial protuberance, outer margin of protuberance predominantly concave (L. sumigarensis with hook-like modification of the lobed protuberance); C) left mandible without setae at apex of mola, with minute denticles between prostheca and mola; D) six pairs of gills; E) hindwing pads absent; F) distolateral process at scape poorly developed or absent; G) colour of larvae dorsally uniform brown.
Examined   Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of ca. 15 clavate setae; B) labial palp segment II with a large, lobed distomedial protuberance, segment III slightly pentagonal, apically slightly truncate; C) left mandible without setae at apex of mola; D) fore femur rather slender, length 3.6× maximum width, dorsal margin with a row of ca. ten curved, spine-like setae; E) tarsal claw with ca. eleven denticles; F) paraproct distally not expanded, with > 40 stout marginal spines.
Colouration. Head, thorax, and abdomen dorsally brown, head, and thorax with bright median, dorsal suture, thorax with pattern as in Fig. 48b, forewing pads with bright striation. Head, thorax, and abdomen ventrally light brown, caudal filaments light brown.
Antenna with scape and pedicel subcylindrical, with poorly developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 16a, b). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 20-23 long, clavate setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid setae; ventral surface with six short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 16c, d). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex, with minute setae. Tuft of setae at apex of mola present.
Left mandible (Fig. 16e, f ). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola absent. Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface. Hypopharynx (Fig. 16g). Lingua approx. as long as superlingua. Lingua longer than broad; medial tuft of stout setae well developed; distal half laterally expanded. Superlingua straight; lateral margin rounded; fine, long, simple setae along distal margin.
Maxilla (Fig. 16h). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and 3-4 medium, simple setae. Maxillary palp 1.2× as long as length of galea-lacinia; two segmented; palp segment II 1.3× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with slight excavation at inner distolateral margin.
Labium (Fig. 16i). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight spine-like setae increasing in length distally; apex with two long and one medium, robust setae; outer margin with 4-6 long, spine-like setae increasing in length distally; ventral surface with short, fine, simple, scattered setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and three medium, simple setae in anteromedial area; dorsally with a row of four or five long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.6× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with two long, spine-like, simple setae near outer margin. Segment III oblong; apex rounded; length 1.1× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg ( Fig. 17a, b, c, d). Ratio of foreleg segments 1.2:1.0:0.5:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of 9-12 curved, spine-like setae; length of setae 0.23× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch poorly developed. Tibia. Dorsal margin with a row of stout, lanceolate setae. Ventral margin with a row of short, curved, spinelike setae, on apex two bipectinate, spine-like setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/3. Tarsus. Dorsal margin bare. Ventral margin with a row of spine-like, bipectinate setae. Tarsal claw with one row of eleven denticles; distally pointed; with four stripes; subapical setae absent.
Tergum (Fig. 17e). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae and micropores. Posterior margin of tergum IV with triangular spines, wider than long.
Gills (Fig. 17f ). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and 1/2 VI combined. Gill VII as long as length of segments VIII and 1/4 IX combined.  Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of 21-24 clavate setae; B) labial palp segment II with a large, lobed distomedial protuberance, segment III slightly pentagonal; C) left mandible without setae at apex of mola; D) fore femur rather slender, length 3.7× width, dorsal margin with a row of ca. 14 curved, spine-like setae and fine, simple setae; E) paraproct distally expanded, with ca. 45 stout marginal spines.
Antenna with scape and pedicel subcylindrical, with poorly developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 18a, b). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 21-24 long, clavate setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid setae; ventral surface with five short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 18c, d). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex, with minute denticles. Tuft of setae at apex of mola present.
Left mandible (Fig. 18e, f ). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola absent. Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Hypopharynx (Fig. 18g). Lingua approx. as long as superlingua. Lingua longer than broad; medial tuft of stout setae well developed; distal half not expanded. Superlingua straight; lateral margin rounded; fine, long, simple setae along distal margin. Maxilla (Fig. 18h). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and four long, simple setae. Maxillary palp 1.4× as long as length of galea-lacinia; two segmented; palp segment II 1.1× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with excavation at inner distolateral margin.
Labium (Fig. 18i). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with seven spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae; outer margin with five spine-like setae increasing in length distally; ventral surface with short, fine, simple, scattered setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and a row of four medium, simple setae in anteromedial area; dorsally with a row of four long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with large, lobed distomedial protuberance; distomedial protuberance 0.8× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with two long, spine-like, simple setae near outer margin. Segment III slightly pentagonal; apex slightly truncate; length 1.1× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg ( Fig. 19a, b, c, d). Ratio of foreleg segments 1.2:1.0:0.4:0.1. Femur. Length ca. 4× maximum width. Dorsal margin with a row of ca. 14 curved, spine-like setae and fine, simple setae; length of setae 0.19× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of stout, apically rounded setae and fine simple setae. Ventral margin with a row of curved, spine-like setae, on apex some spine-like, partly bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/3. Tarsus. Dorsal margin almost bare. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 10-12 denticles; distally pointed; with three stripes; subapical setae absent.
Tergum (Fig. 19e). Surface with rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergum IV with triangular spines, wider than long.
Gills (Fig. 19f ). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and 1/3 VI combined. Gill VII as long as length of segment VIII.
Etymology. Dedicated to the indigenous Lubu people from Sumatra. Distribution. Indonesia: Sumatra. Biological aspects. The specimens were collected in a creek at an altitude of 1,050 m.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture. Head, thorax, and abdomen ventrally light brown, legs transparent, caudal filaments light brown.
Antenna with scape and pedicel subcylindrical, without distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 20a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with long, fine, simple setae scattered over surface; submarginal arc of setae composed of 18-19 long, clavate setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid setae; ventral surface with five short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 20b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex. Tuft of setae at apex of mola present.
Left mandible (Fig. 20d, e). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola absent.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 20g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and 3-4 medium, simple setae. Maxillary palp 1.4× as long as length of galea-lacinia; two segmented; palp segment II 1.3× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with slight excavation at inner distolateral margin. Labium (Fig. 20h, i). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with 4-6 spine-like setae increasing in length distally; apex with two long and one medium, robust setae; outer margin with 4-6 long, spine-like setae increasing in length distally; ventral surface with short, fine, simple, scattered setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and a row of three or four medium, simple setae in anteromedial area; dorsally with a row of three long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with large, lobed distomedial protuberance; distomedial protuberance 0.8× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with two long, spine-like, simple setae near outer margin. Segment III slightly pentagonal; apex slightly truncate; length 1.2× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 21a, b). Ratio of foreleg segments 1.3:1.0:0.5:0.2. Femur. Length ca. 4× maximum width. Dorsal margin with a row 12-15 spine-like setae and many fine, simple setae; length of setae 0.23× maximum width of femur. Apex rounded; with 1-2 pairs of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch poorly developed. Tibia. Dorsal margin with a row of short, stout setae (not always present) and fine, simple setae. Ventral margin with a row of short, spine-like setae, on apex some stout, spine-like, partially bipectinate setae and a tuft of fine, simple setae. Patellotibial suture present on basal 1/3. Tarsus. Dorsal margin with a row of fine, simple setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 10-11 denticles; distally pointed; with three stripes; subapical setae absent.
Tergum (Fig. 21c). Surface with rows of U-shaped scale bases and scattered micropores. Posterior margin of tergum IV with triangular spines, wider than long. Gills (Fig. 21d). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and VI combined. Gill VII as long as length of segments VIII and 1/2 IX combined.
Description. Larva (Figs 22,23,49a). Body length 6.0 mm. Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture, thorax with bright pattern as in Fig. 49a, abdominal segments IX and X light brown, forewing pads with dark brown striation and bright striation near margin. Head, thorax, and abdomen ventrally light brown, legs transparent, ventral margin of femur brown, caudal filaments light brown.
Antenna with scape and pedicel subcylindrical, with poorly developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 22a, b). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 20-24 long, clavate setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid setae; ventral surface with six short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 22c, d). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex, with minute denticles. Tuft of setae at apex of mola present.
Left mandible (Fig. 22e, f ). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola absent.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 22h). Galea-lacinia with one simple, robust apical seta under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and five long, simple setae. Maxillary palp 1.3× as long as length of galea-lacinia; two segmented; palp segment II 1.4× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with slight excavation at inner distolateral margin.
Labium (Fig. 22i). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae; outer margin with 4-5 long, spine-like setae increasing in length distally; ventral surface with short, fine, simple setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and four medium, simple setae in anteromedial area; dorsally with a row of three long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.7× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of 3-4 long, spine-like, simple setae near outer margin. Segment III slightly pentagonal; apex slightly pointed; length 1.2× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 23a, b, c). Ratio of foreleg segments 1.2:1.0:0.5:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. 16 curved, spine-like setae; length of setae 0.21× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch poorly developed. Tibia. Dorsal margin bare. Ventral margin with a row of curved, spine-like setae, on apex two bipectinate, spine-like setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin bare. Ventral margin with a row of curved, spine-like, bipectinate setae. Tarsal claw with one row of 10-13 denticles; distally pointed; with three stripes; subapical setae absent.
Tergum (Fig. 23d). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae and micropores. Posterior margin of tergum IV with triangular spines, wider than long.
Gills (Fig. 23e). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and 2/3 VI combined. Gill VII as long as length of segments VIII and 1/3 IX combined.
Etymology. Refers to the morphological similarity with L. diffundus. Distribution. Indonesia: Sumatra. Biological aspects. The specimens were collected at altitudes from 890 m to 1,830 m in small to medium (0.5 m -5 m wide), shallow (5 cm -10 cm deep) and slow to medium fast (velocity 0.2 m/s -0.7 m/s) forest streams or, in one case, a highly disturbed stream (agriculture, waste). The substrate was predominantly bedrock, boulder, stones, gravel and sand and only rarely with leaf litter or dead wood. Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of 20 clavate setae; B) labial palp segment II with an elongated, thumb-like distomedial protuberance, segment III slightly pentagonal, apically with a small projection; C) left mandible without setae at apex of mola; D) maxillary palp much longer than galea-lacinia, apically rounded and curved inward, with excavation at inner distolateral margin; E) fore femur rather slender, length ca. 4× maximum width, dorsal margin with a row of 10-13 curved, spine-like setae; F) paraproct distally not expanded, with ca. 32 stout marginal spines.
Colouration. Head and thorax dorsally brown, with bright median, dorsal suture, thorax with pattern as in Fig. 49b, forewing pads with dark striation. Abdomen dorsally reddish-brown. Head, thorax, and abdomen ventrally light brown, legs transparent with brown spots distomedially on femur, caudal filaments light brown.
Antenna with scape and pedicel subcylindrical, without distolateral process at scape; flagellum with broad, lanceolate spines and fine, simple setae on apex of each segment. Labrum (Fig. 24a, b). Rectangular, length 0.6× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 20 long, clavate setae.
Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid setae; ventral surface with five short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 24c, d). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola straight. Tuft of setae at apex of mola present.
Left mandible (Fig. 24e, f ). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola absent.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 24h, i). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and 3-4 medium, simple setae. Maxillary palp 1.5× as long as length of galea-lacinia; two segmented; palp segment II 1.4× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded and curved inward, with excavation at inner distolateral margin.
Labium (Fig. 24j). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with six spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae; outer margin with 4 long, spine-like setae; ventral surface with short, fine, simple setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and 4-5 medium, simple setae in anteromedial area; dorsally with a row of four long, spine-like setae near inner margin. Labial palp with segment I approx. as long as length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with elongated, thumb-like distomedial protuberance; distomedial protuberance 0.8× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with two long, spine-like, simple setae near outer margin. Segment III slightly pentagonal; apex with small projection; length 1.0× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Foreleg (Fig. 25a, b, c, d). Ratio of foreleg segments 1.2:1.0:0.4:0.1. Femur. Length ca. 4× maximum width. Dorsal margin with a row of 10-13 curved, spinelike, apically rounded setae; length of setae 0.22× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae, some short stout setae and some fine, simple setae. Short to medium stout, lanceolate setae scattered along the ventral margin; femoral patch reduced to a few setae. Tibia. Dorsal margin with a row of minute, stout setae and fine, simple setae. Ventral margin with a row of curved, spinelike setae, on apex some stout, spine-like and partly bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/3. Tarsus. Dorsal margin with a row of fine, simple setae. Ventral margin with a row of curved, spine-like, bipectinate setae (pectination dif-ficult to see). Tarsal claw with one row of 9-10 denticles; distally pointed; with two stripes; subapical setae absent.
Tergum (Fig. 25e). Surface with rows of U-shaped scale bases and scattered micropores. Posterior margin of tergum IV with triangular spines, wider than long.
Gills (Fig. 25f ). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and 1/2 VI combined. Gill VII as long as length of segments VIII and 1/4 IX combined.

Labiobaetis gueuningi group of species
With the following combination of characters: A) dorsal surface with submarginal arc of simple setae; B) labial palp segment II with thumb-like distomedial protuberance; C) maxillary palp with three segments; D) seven pairs of gills; E) spines at posterior margin of abdominal terga with medial enhancement; F) hindwing pads absent; G) distolateral process at scape well developed.
Antenna with scape and pedicel subcylindrical, with well-developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 26a). Rectangular, length 0.8× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of nine or ten medium to long, simple setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with four short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 26b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola straight. Tuft of setae at apex of mola present.
Left mandible (Fig. 26d, e). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 26g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spinelike seta and five medium to long, simple setae. Maxillary palp 1.3× as long as length of galea-lacinia; three segmented; palp segment II approx. as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I, II and III; palp segment III shorter than segment II; apex of last segment slightly pointed, without excavation at inner distolateral margin.
Labium (Fig. 26h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with ten or eleven spine-like setae; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with 5-7 spine-like setae; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and one or two medium, simple setae in anteromedial area; dorsally with a row of six long, spine-like setae near inner margin. Labial palp with segment I 0,7× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.5× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of four long, spine-like, simple setae near outer margin. Segment III conical; apex with small projection; length 0.9× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 27a, b, c, d). Ratio of foreleg segments 1.4:1.0:0.7:0.3. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. 14 clavate setae, apically with minute serration; length of setae 0.14× maximum width of femur. Apex rounded; with one pair of clavate setae with apical minute serration and some short, stout setae. Many stout, lanceolate, apically rounded setae scattered along the ventral margin; femoral patch poorly developed. Tibia. Dorsal margin with a row of short, stout setae and fine, simple setae, along margin a row of lanceolate, apically rounded setae; on apex one long, clavate seta with minute apical serration. Ventral margin with a row of curved, spine-like setae, on apex some bipectinate, spine-like setae and a tuft of simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 2/3. Tarsus. Dorsal margin with a row of short, stout setae, on apex fine, simple setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of ten or eleven denticles; distally pointed; with 5-6 stripes; subapical setae absent.
Tergum (Fig. 27e, f ). Surface with rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergum IV with triangular spines, wider than long and with medial enhancement.
Gills (Fig. 27g). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I as long as length of segment II. Gill IV as long as length of segments V and VI combined. Gill VII as long as length of segments VIII and 1/3 IX combined.
Etymology. Dedicated to Morgan Gueuning, who collected the specimens in Sumatra. Distribution. Indonesia: Sumatra. Biological aspects. The specimens were collected at altitudes of 840 m to 1,300 m in small to medium (0.5-5 m wide), shallow (7-40 cm deep) and slow to medium fast (velocity 0.2-0.8 m/s) streams in forest or in highly disturbed areas (agriculture, waste). The substrate was predominantly boulder, stones, gravel and sand with few patches of leaf litter of dead wood. Type
Colouration. Colouration of head, thorax, and abdomen unknown due to DNA extraction from all specimens in an earlier project. Femur along dorsal and ventral margin brown, tibia and tarsus brown.
Antenna with scape and pedicel subcylindrical, with well-developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 28a). Rectangular, length 0.8× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of eleven medium to long, simple setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with five short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 28b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola straight. Tuft of setae at apex of mola present.
Left mandible (Fig. 28d, e). Incisors fused. Outer and inner sets of denticles with 3 + 4 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 28g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spinelike seta and seven or eight simple setae increasing in length distally. Maxillary palp 1.3× as long as length of galea-lacinia; three segmented; palp segment II 1.4× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I, II and III; palp segment III shorter than segment II; apex of last segment slightly pointed, without excavation at inner distolateral margin. Labium (Fig. 28h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with 13 spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae; outer margin with ten or eleven spine-like setae; ventral surface with short, fine, simple setae. Paraglossa subrectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in anteromedial area; dorsally with a row of seven or eight long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.6× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of 4-6 medium, spine-like setae near outer margin. Segment III oblong; apex with small projection; length 1.3× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 29a, b). Ratio of foreleg segments 1.3:1.0:0.7:0.2. Femur. Length ca. 4× maximum width. Dorsal margin with a row of 12-15 curved, spine-like setae; length of setae 0.16× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate, apically rounded setae scattered along the ventral margin; femoral patch well developed. Tibia. Dorsal margin with a row of short, stout setae and a few lanceolate, apically rounded setae along margin; on apex one longer, spine-like seta. Ventral margin with a row of curved, spine-like setae, on apex one bipectinate, spine-like seta and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 2/3. Tarsus. Dorsal margin with a row of short, stout setae, on apex fine, simple setae. Ventral margin with a row of curved, spinelike setae. Tarsal claw with one row of 12 denticles; distally pointed; with five stripes; subapical setae absent.
Tergum (Fig. 29c). Surface with rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergum IV with triangular spines, wider than long and with medial enhancement. Gills (Fig. 29d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I as long as length of segment II. Gill IV as long as length of segments V and 1/2 VI combined. Gill VII as long as length of segments VIII and 1/3 IX combined.

Labiobaetis numeratus group of species
With the following combination of characters: A) dorsal surface with submarginal arc of simple setae; B) labial palp segment II with thumb-like distomedial protuberance; C) right mandible with a pronounced hump between prostheca and mola; D) six pairs of gills; E) hindwing pads present, minute; F) distolateral process at scape absent. Figure 30, 53b

Labiobaetis paranumeratus sp. nov.
http://zoobank.org/551F3B4B-4F90-4433-A26A-8E305E6A3024 Figures 31, 32, 50a, 54b Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of 1 + 8 medium to long, simple setae, the first two setae after the central seta are closely together; B) right mandible with a pronounced hump between prostheca and mola; C) labial palp segment II with a broad thumb-like distomedial protuberance, segment III conical; D) fore femur rather broad, length ca. 3× maximum width, dorsal margin with ca. seven spine-like setae, apically rounded and with minute serration, close to margin some spine-like setae, apically rounded and with minute pectination; E) paraproct distally not expanded, with ca. 17 stout marginal spines and some submarginal spines.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture, forewing pads light brown with darker striation. Head, thorax, and abdomen ventrally brown, legs transparent, femur distomedially with a brown spot, tibia distomedially and tarsus proximally brown. Caudal filaments light brown, with a dark brown band at 2/3 of cerci.
Antenna with scape and pedicel subcylindrical, without distolateral process at scape; flagellum with broad, apically blunt spines and fine, simple setae on apex of each segment.
Labrum (Fig. 31a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 8 medium to long, simple setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with seven short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 31b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola with a pronounced hump. Tuft of setae at apex of mola present.
Left mandible (Fig. 31d, e). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola slightly convex, with minute denticles toward subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins slightly convex. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 31g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spinelike seta and four or five long, simple setae. Maxillary palp 1.6× as long as length of galea-lacinia; two segmented; palp segment II 1.6× length of segment I; setae on maxil- lary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, without excavation at inner distolateral margin.
Labium (Fig. 31h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight spine-like setae, distalmost seta much longer than other setae; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with six long spine-like setae increasing in length distally; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and four medium, simple setae in anteromedial area; dorsally with a row of six long, spine-like setae near inner margin. Labial palp with segment I 0.9× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.8× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of four short to medium, spine-like, simple setae near outer margin. Segment III conical; apex rounded; length 0.9× width; ventrally covered with short and medium spine-like, simple setae and short, fine, simple setae.
Hind wing pads minute. Foreleg (Fig. 32a, b, c, d, e). Ratio of foreleg segments 1.3:1.0:0.6:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. seven spine-like setae, apically rounded and with minute serration, close to margin some spine-like setae, apically rounded and with minute serration; length of setae 0.27× maximum width of femur. Apex rounded; with one pair of spine-like setae, apically rounded and with minute pectination and with some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of stout setae, apically rounded and with minute pectination; on apex one pair of long, stout setae, apically rounded and with minute pectination. Ventral margin with a row of curved, spine-like setae, on apex some spine-like, bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin almost bare. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 13-14 denticles; distally pointed; with five stripes; subapical setae absent.
Tergum (Fig. 32f ). Surface with irregular rows of scale bases and scattered micropores. Posterior margin of tergum IV with rounded spines, wider than long. Gills (Fig. 32g). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and 2/3 VI combined. Gill VII as long as length of segments VIII and 2/3 IX combined.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture, abdominal segments with pattern as in Fig. 50b, forewing pads with bright striation. Head, thorax, and abdomen ventrally brown, abdominal segment X light brown, legs light brown, dorsal margin of femur brown, caudal filaments light brown and with a dark brown band at 1/3 of cerci.
Antenna with scape and pedicel subcylindrical, without distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 33a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 6-8 long, simple setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with six short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 33b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola with a pronounced hump and minute denticles on margin of hump. Tuft of setae at apex of mola present.
Left mandible (Fig. 33d, e). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola slightly convex, with minute denticles toward subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 33g). Galea-lacinia with one simple, robust apical seta under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and five long, simple setae. Maxillary palp 1.6× as long as length of galealacinia; two segmented; palp segment II 1.4× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II, very dense on segment II; apex of last segment slightly pointed, with excavation at inner distolateral margin.
Labium (Fig. 33h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with nine or ten spine-like setae, distalmost seta much longer and less robust than other setae; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with 5-7 spine-like setae increasing in length distally; ventral surface with short, fine, simple, scattered setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area; outer margin with row of three long, spine-like setae and 4-7 medium, simple setae in anteromedial area; dorsally with a row of 4-5 long, spinelike setae near inner margin. Labial palp with segment I 0.6× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with thumb-like distomedial protuberance; distomedial protuberance 0.6× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of 5-7 medium, spine-like, simple setae near outer margin. Segment III conical; apex slightly truncate; length 1.1× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads minute. Foreleg (Fig. 34a-c). Ratio of foreleg segments 1.2:1.0:0.5:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of 12-16 curved, spine-like setae and many spine-like, apically rounded setae along margin; length of setae 0.19× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin, femoral patch absent. Anterior surface covered with fine, simple setae. Tibia. Dorsal margin with a row of curved, spine-like setae; on apex a pair of longer, spine-like setae. Ventral margin with a row of curved, spine-like setae, on apex several stout, partly bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae and covered with fine, simple setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, spine-like setae and fine, simple setae. Ventral margin with a row of curved, spine-like setae. Anterior surface covered with fine, simple setae. Tarsal claw with one row of 11-14 denticles; distally pointed; with five stripes; subapical setae absent.
Tergum (Fig. 34d). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergum IV with triangular spines, approx. as long as wide.
Gills (Fig. 34e). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill IV as long as length of segments V and 2/3 VI combined. Gill VII as long as length of segments VIII and 1/3 IX combined.

Labiobaetis operosus group of species
With the following combination of characters: A) dorsal surface of labrum with submarginal arc of feathered setae; B) labial palp segment II with thumb-like distomedial protuberance; C) seven pairs of gills; D) hindwing pads well developed; E) distolateral process at scape well developed.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture, thorax and abdomen with pattern as in Fig. 51d. Forewing pads light brown at base and with light brown distal spots. Head, thorax, and abdomen ventrally very light brown, abdominal segments VIII and IX brown. Legs transparent, femur with a distomedial, brown spot and brown apex, caudal filaments transparent with a dark brown band at ca. 1/3 of cerci.
Antenna with scape and pedicel subcylindrical, with well-developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 36a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae; submarginal arc of setae composed of 1 + 9 or10 long, feathered setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with three short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 36b, c). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles and one minute intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola straight. Tuft of setae at apex of mola present.
Left mandible (Fig. 36d, e). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 36g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and 4-5 long, simple setae. Maxillary palp 1.4× as long as length of galea-lacinia; two segmented; palp segment II 1.3× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with slight excavation at inner distolateral margin.
Labium (Fig. 36h, i). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight or nine spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with 5-7 spine-like setae increasing in length distally; ventral surface with short, fine, simple, scattered setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two or three medium, simple setae in anteromedial area and partly one short, simple seta in proximomedial area; dorsally with a row of four or five long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with broad thumb-like distomedial protuberance; distomedial protuberance 0.9× width of base at segment III; inner and outer margin with short, fine, simple setae; dorsally with two long, spine-like, simple setae near outer margin. Segment III oblong; apex rounded; length 1.5× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads well developed. Foreleg (Fig. 37a, b). Ratio of foreleg segments 1.2:1.0:0.5:0.2. Femur. Length ca. 4× maximum width. Dorsal margin with a row of 11-18 spine-like setae and one or two spine-like setae near margin; length of setae 0.25× maximum width of femur. Apex rounded; with one pair of curved, spine-like setae and some short, stout setae. Many short, stout, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of short, stout setae; on apex one longer seta, and a row of short, stout setae close to dorsal margin. Ventral margin with a row of curved, spinelike setae, distally longer, on apex one bipectinate, spine-like seta and a tuft of long, fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, stout setae and long, fine, simple setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of 9-11 denticles; distally pointed; with 3-5 stripes; subapical setae absent.
Tergum (Fig. 37c). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergum IV with triangular spines, wider than long. Gills (Fig. 37d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I ca. 2/3 length of segment II. Gill IV as long as length of segments V and 1/3 VI combined. Gill VII as long as length of segment VIII.
Etymology. Refers to the morphological similarity with L. operosus. Distribution. Indonesia: Sumatra. Biological aspects. The specimens were collected at altitudes between sea level and 890 m, one of them in a small (2 m wide), shallow (25 cm deep) and slow (velocity 0.3 m/s) stream in a highly disturbed area (agriculture, livestock, waste). The substrate was predominantly stone and gravel without patches of leaf litter or dead wood. Type

Labiobaetis seramensis group of species
With the following combination of characters: A) dorsal surface of labrum with submarginal arc of simple setae; B) labial palp segment II with slender or rather slender, thumb-like distomedial protuberance, segment III approx. semi-circular; C) maxillary palp approx. as long as galea-lacinia; D) six pairs of gills; E) hindwing pads absent; F) distolateral process at scape absent.
Colouration. Head, thorax, and abdomen dorsally brown, head and thorax with bright median, dorsal suture, thorax with bright pattern as in Fig. 50c, forewing pads with darker striation, abdominal segment VI with bright areas as in Fig. 50c, abdominal segments IX and X light brown. Head, thorax, and abdomen ventrally light brown, legs transparent, femur with brown dorsal margin, caudal filaments transparent.
Antenna with scape and pedicel subcylindrical, without distolateral process at scape; flagellum with broad, lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 38a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae and a few short, slightly lanceolate setae; submarginal arc of setae composed of 1 + 2 long, simple setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with six short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 38b, c). Incisors fused. Outer and inner sets of denticles with 4 + 4 denticles. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex. Tuft of setae at apex of mola present.
Left mandible (Fig. 38d, e). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles and one minute intermediate denticle. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with minute denticles towards subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Hypopharynx (Fig. 38f ). Lingua approx. as long as superlingua. Lingua approx. as broad as long; medial tuft of stout setae well developed, long; distal half not expanded. Superlingua straight; lateral margin rounded; fine, long, simple setae along distal margin.
Maxilla (Fig. 38g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and five long, simple setae. Maxillary palp approx. as long as length of galea-lacinia; two segmented; palp segment II 1.5× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment slightly pointed, with slight excavation at inner distolateral margin.
Labium (Fig. 38h). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with five spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with four long, spine-like setae; ventral surface with short, fine, simple and short, spine-like setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and three medium, simple setae in anteromedial area and one fine, simple seta in proximomedial area; dorsally with a row of four long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with slender, thumb-like distomedial protuberance; distomedial protuberance 0.4× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of four medium, spinelike setae near outer margin. Segment III approximately semi-circular; apex rounded; length 1.1× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 39a, b). Ratio of foreleg segments 1.3:1.0:0.6:0.2. Femur. Length ca. 3× maximum width. Dorsal margin with a row of ca. 21 curved, spine-like setae and a few spine-like setae near margin; length of setae 0.25× maximum width of femur. Apex rounded; with a few short, stout, pointed setae. Many short to long, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of short, stout setae. Ventral margin with a row of curved, spine-like setae, on apex one to several stout, spine-like setae and a tuft of long, fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin almost bare. Ventral margin with a row of curved spine-like setae. Tarsal claw with one row of ten denticles; distally pointed; with four stripes; subapical setae absent.
Tergum (Fig. 39c). Surface with irregular rows of U-shaped scale bases and scattered micropores. Posterior margin of tergum IV with triangular spines, approx. as long as wide.
Gills. Present on segments II-VII. Paraproct (Fig. 39d). Distally not expanded, with ca. 15 stout marginal spines and some submarginal spines. Surface scattered with U-shaped scale bases and fine, simple setae. Cercotractor with numerous small marginal spines and some submarginal spines.
Antenna with scape and pedicel subcylindrical, without distolateral process at scape; flagellum with broad, lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 40a). Rectangular, length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 5 long, simple setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with seven short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 40b, c). Incisors fused. Outer and inner sets of denticles with 4 + 4 denticles and one small intermediate denticle. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola slightly convex, with minute denticles. Tuft of setae at apex of mola present.
Left mandible (Fig. 40d, e). Incisors fused. Outer and inner sets of denticles with 4 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola slightly convex, with minute denticles toward subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Hypopharynx (Fig. 40f ). Lingua approx. as long as superlingua. Lingua approx. as broad as long; medial tuft of stout setae well developed, short; distal half not expanded. Superlingua rounded; lateral margin rounded; fine, long, simple setae along distal margin.
Maxilla (Fig. 40g). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and six long, simple setae. Maxillary palp approx. as long as length of galea-lacinia; two segmented; palp segment II 1.2× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment slightly pointed, without excavation at inner distolateral margin.
Labium (Fig. 40h, i). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with eight spine-like setae increasing in length distally; apex with two long and one medium, robust, pectinate setae and one short, robust seta; outer margin with 6-8 spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and three medium, simple setae in anteromedial area and one fine, simple seta in proximomedial area; dorsally with a row of five long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short and medium, fine, simple setae. Segment II with thumb-like distomedial protuberance; distomedial protuberance 0.6× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of four medium, spine-like setae near outer margin. Segment III approx. semi-circular; apex rounded; length 0.9× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 41a, b). Ratio of foreleg segments 1.1:1.0:0.4:0.2. Femur. Length ca. 4× maximum width. Dorsal margin with Dorsal margin with a row of ca. 22 curved, spine-like setae and a row of spine-like setae along margin; length of setae 0.11× maximum width of femur. Apex rounded; with one pair of spine-like setae and some shorter, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch absent. Tibia. Dorsal margin with a row of stout, lanceolate setae and many stout, lanceolate setae scattered along the margin. Ventral margin with a row of curved, spine-like setae, on apex some stout, spine-like, partly bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/3. Tarsus. Dorsal margin with a row of short, spine-like setae. Ventral margin with a row of curved, spine-like setae. Tarsal claw with one row of ten denticles; distally pointed; with five stripes; subapical setae absent.
Tergum (Fig. 41c). Surface with irregular rows of U-shaped scale bases and scattered micropores. Posterior margin of tergum IV with triangular spines, longer than wide.
Gills (Fig. 41d). Present on segments II-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill VII as long as length of segments VIII and 1/3 IX combined.
Paraproct (Fig. 41e) Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of nine or ten feathered setae; B) labial palp segment II with a large, lobed distomedial protuberance, segment III oblong, apically slightly pointed; C) fore femur rather slender, length 3.6× maximum width, dorsal margin with a row of 11-13 curved, spine-like setae; D) seven pairs of gills; E) hindwing pads present, small; F) distolateral process at scape well developed.

Labiobaetis moriharai (Müller-Liebenau, 1984) Figures 43, 53b
Diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submarginal arc of 1 + 8-10 simple setae, the first three after the central seta are longer than the others and decreasing in length; B) labial palp segment II with a large, lobed distomedial protuberance, segment III conical, apically slightly truncate; C) fore femur rather broad, length 3.4× maximum width, dorsal margin with a row of ca. ten curved, spine-like setae; D) six pairs of gills; E) hindwing pads present, minute; F) distolateral process at scape well developed; G) paraproct distally not expanded, with ca. 12 stout marginal spines.
Description. Larva (Figs 45,46,51b,c,52f ). Body length 6.8-7.6 mm; antenna approximately 3× as long as head length.  Colouration. Head, thorax, and abdomen dorsally brown to dark brown, head and thorax with bright median, dorsal suture; thorax and abdomen with bright pattern as in Fig. 51b, c; forewing pads with dark striation and mature larva additionally with bright striation close to margin. Head, thorax, and abdomen ventrally light brown to dark brown, legs with yellowish and brown pattern as in Fig. 52f, mouthparts including maxillary and labial palp brown. Caudal filaments brown with a darker section in the middle part.
Antenna with scape and pedicel subcylindrical, with well-developed distolateral process at scape; flagellum with lanceolate spines and fine, simple setae on apex of each segment.
Labrum (Fig. 45a, b). Rectangular, length 0.8× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submarginal arc of setae composed of 1 + 6 long, feathered setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae; ventral surface with eight short, spine-like setae near lateral and anterolateral margin.
Right mandible (Fig. 45c, d). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles. Inner margin of innermost denticle with a row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola straight. Tuft of setae at apex of mola present.
Left mandible (Fig. 45e, f ). Incisors fused. Outer and inner sets of denticles with 3 + 3 denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight. Subtriangular process long and slender, above level of area between prostheca and mola. Denticles of mola apically constricted. Tuft of setae at apex of mola present.
Both mandibles with lateral margins almost straight. Basal half with fine, simple setae scattered over dorsal surface.
Maxilla (Fig. 45h). Galea-lacinia with two simple, robust apical setae under crown. Inner dorsal row of setae with three denti-setae, distal denti-seta tooth-like, middle and proximal denti-setae slender, bifid and pectinate. Medially with one bipectinate, spine-like seta and six long, simple setae. Maxillary palp 1.4× as long as length of galealacinia; two segmented; palp segment II 1.3× length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment rounded, with excavation at inner distolateral margin.
Labium (Fig. 45i, j). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with 9-11 spine-like setae increasing in length distally; apex with two long and one medium, robust setae; outer margin with nine or ten long, spine-like setae increasing in length distally; ventral surface with short, fine, simple setae. Paraglossa sub-rectangular, curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and a row of four medium, simple setae in anteromedial area; dorsally with a row of six or seven long, spine-like setae near inner margin. Labial palp with segment I 0.8× length of segments II and III combined. Segment I ventrally with short, fine, simple setae and some short, stout, simple setae at inner margin. Segment II with thumb-like distomedial protuberance; distomedial protuberance 0.6× width of base of segment III; inner and outer margin with short, fine, simple setae; dorsally with a row of eight medium, spine-like, simple setae near outer margin. Segment III oblong; apex slightly pointed; length 1.3× width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.
Hind wing pads absent. Foreleg (Fig. 46a, b). Ratio of foreleg segments 1.2:1.0:0.5:0.2, or 1.1:1.0:0.4:0.1. Femur. Length ca. 4× maximum width. Dorsal margin with a row of ca. 13 spine-like setae and some spine-like setae near margin; length of setae 0.16× maximum width of femur. Apex rounded; with one pair of spine-like setae and some short, stout setae. Many stout, lanceolate setae scattered along the ventral margin; femoral patch reduced to a few setae. Tibia. Dorsal margin with a row of stout, lanceolate setae and additional stout, lanceolate setae near margin. Ventral margin with a row of curved, spine-like setae, on apex several spine-like, bipectinate setae and a tuft of fine, simple setae. Anterior surface scattered with stout, lanceolate setae. Patellotibial suture present on basal 1/2. Tarsus. Dorsal margin with a row of short, spine-like setae and additional stout, lanceolate setae near margin. Ventral margin with a row of curved, spine-like setae and some spine-like setae near margin. Tarsal claw with one row of 13 denticles; distally pointed; with seven or eight stripes; subapical setae absent.
Tergum (Fig. 46c). Surface with irregular rows of U-shaped scale bases and scattered micropores. Posterior margin of tergum IV with triangular spines, longer than wide.
Gills (Fig. 46d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I as long as length of segment II. Gill IV as long as length of segments V, VI, and 1/4 VII combined. Gill VII as long as length of segments VIII and IX combined.

Key to the Labiobaetis species of Indonesia and adjacent countries (larvae)
1 Dorsal surface of labrum with submarginal arc of simple setae (Fig. 1a) ............2 -Dorsal surface of labrum with submarginal arc of clavate setae (Fig. 1c) ..........11 -Dorsal surface of labrum with submarginal arc of feathered setae (Fig. 1b)  Hindwing pads absent (Fig. 1v)  Paraproct distally not expanded; hypopharynx with medial tuft of stout setae well developed, long (Fig. 1r); labial palp segment II enlargement slender, thumb-like (Fig. 1i) -Liebenau (1982-Liebenau ( , 1984a and Soldan (1991). Labiobaetis diffundus and L. numeratus were also reported from China (Shi and Tong 2014) and L. molawinensis from Taiwan (Kang et al. 1994). However, based on the illustrations of Kang et al. (1994: fig. 15), this is, in our opinion, neither L. molawinensis, as already stated by Shi and Tong (2014), nor L. diffundus, as there seems to be no antennal scape process at all. The recent material treated in this study was collected in 50 locations across Indonesia (Fig. 53a). There are still many regions in Indonesia and Southeast Asia in general where no sampling of mayflies has yet been done and many species are known from a single population only. This implies that the current diversity and distribution must be considered as very preliminary. In terms of altitude, the Labiobaetis species of Indonesia were found from sea level to mountain areas up to 2,000 m. The GPS coordinates of the locations in Indonesia and adjacent countries are given in Table 2.   nov. The exceptions are L. pilosus sp. nov., and L. batakorum sp. nov. Three of the four sequenced specimens of L. pilosus sp. nov. have distances from 0% to 1%, but the fourth specimen collected in another location has a distance of 3% to 4% compared to the others. Labiobaetis batakorum sp. nov. presents an intraspecific distance of 0% to 4% (avg. 2.5%) between the four sequenced specimens from three different locations.

Discussion
For the assignment of the new species to Labiobaetis we refer to Kluge and Novikova (2014), Müller-Liebenau (1984a), and McCafferty and Waltz (1995). Labiobaetis is characterized by a number of derived characters, some of which are not found in other taxa (Kluge and Novikova 2014): antennal scape sometimes with a distolateral process ( Fig. 1d-f ); maxillary palp two-segmented with an excavation at inner dis-tolateral margin of segment II, excavation may be poorly developed or absent (Figs. 1 o-q); labium with paraglossae widened and glossae diminished; and labial palp segment II with distomedial protuberance (Figs. 1 g-j). All these characters vary and may be secondarily lost (Kluge and Novikova 2014). Two of the species described in this study (L. gueuningi sp. nov. and L. minang sp. nov.) have a maxillary palp with three segments, which was also described from Labiobaetis boussoulius (Gillies) from Guinea (Gillies 1993). The concept of Labiobaetis is also based on additional characters (Müller-Liebenau 1984a, McCafferty and Waltz 1995, Lugo-Ortiz and McCafferty 1997, Lugo-Ortiz et al. 1999, slightly amended based on the discovery of the 18 new species: dorsal surface of labrum with submarginal setae arranged in one arc, the setae may belong to a simple, pointed type, a feathered type, a dendritic type, a spatulate/clavate type (apically pectinate or smooth) or a lanceolate type (apically pectinate or not pectinate)  fig. 1a-f; mandibles with fused incisors, right prostheca apically denticulate, left prostheca apically denticulate and with a comb-shaped structure; hypopharynx with medial tuft of stout setae at apex of median lobe, the tuft may be well developed and of different lengths or poorly developed ( Fig. 1r-u); paraglossae sub-rectangular, slightly curved inward; hindwing pads well developed, small, minute, vestigial or absent (Fig. 1v-y); femoral patch well developed, rudimentary or absent; tibia at apical margin with a tuft of fine, simple setae; tarsal claw distally pointed with one row of denticles, striation present, subapical setae absent; abdominal terga with irregular rows of numerous U-shaped or rarely W-shaped scale bases, posterior margin with regular, triangular, pentagonal or rounded spines; gills on abdominal segment I present or absent; paraproct with ten to more than 40 marginal spines, lateral ones always smaller and distally expanded, slightly expanded or not expanded at all (Fig. 1z1, (Kluge 2012, Kaltenbach and, but no pectinate setae elsewhere on the legs. The seven species groups proposed in this paper are based on the combination of the types of setae composing the submarginal arc of setae on the dorsal surface of the labrum and the shapes of the distomedial protuberance of labial palp segment II, together with other characters. These morphological groups within Labiobaetis are primarily a working tool but could also serve as a basis for future studies on the generic delimitation and phylogeny of this probably polyphyletic genus. The inclusion of nuclear gene sequences may prove that some may be natural groups. So far there was no overlap of any species distribution found between New Guinea and Southeast Asia of Labiobaetis, nor any shared species groups. The sumigarensis group was proposed by Müller-Liebenau and Hubbard (1985) as a subgroup of the Oriental Baetis molawinensis group, based on the concave outer margin of the large, thumb-like or lobed protuberance of labial palp segment II. They included L. sumigarensis, L. diffundus, L. geminatus (Müller-Liebenau and Hubbard), and an undescribed species from Madagascar in that subgroup. Later, the molawinensis group formed the basis of Labiobaetis together with the European Baetis atrebatinus group and the North American Baetis propinquus group Kluge 1987, McCafferty andWaltz 1995). In our study on Labiobaetis from New Guinea  we placed L. molawinensis (Müller-Liebenau) in the balkei group of species from New Guinea. However, examination of a paratype of L. molawinensis revealed that it should be placed in the sumigarensis group. All characters of the sumigarensis group as described in this paper are present in L. molawinensis; the setae of the submarginal arc on the dorsal surface of the labrum are apically smooth and do not show an apical pectination as in the balkei group, which can be assumed from the drawing in Müller-Liebenau (1982: fig. 4A). Furthermore, L. molawinensis has no setae at the apex of the mola of the left mandible, in line with the sumigarensis group and contrary to the balkei group, a character which is not shown in the drawing of Müller-Liebenau (1982: fig. 4G). Apart from these two characters, both groups are in fact rather similar.
The seraminensis group is also very similar to the claudiae group from New Guinea (shape of the labial palp segment II; the setae of the submarginal arc on the dorsal surface of the labrum are also simple; no hindwing pads, six pairs of gills, no scape process). However, the seramensis group has the usual fine setae of uniform length at the gills margin and no femoral patch and the claudiae group has both shorter and longer fine setae at the gills margin and a well-developed femoral patch.
Labiobaetis borneoensis (Müller-Liebenau) has a lobed distomedial protuberance at labial palp segment II combined with feathered setae of the submarginal arc on the dorsal surface of the labrum as seen in the two species of the orientis group from New Guinea and was, therefore, placed in this group . However, the differences between L. borneoensis and the orientis group are too important to uphold this assignment with the knowledge of the new groups in Indonesia: L. borneoensis has seven pairs of gills, an antennal scape process, and hindwing pads, none of which are present in the orientis group. We therefore do not propose an assignment for borneoensis to any group at the moment.
All other species groups from New Guinea (petersorum group, tuberpalpus group, vitilis group, vultuosus group) significantly differ from any other group or species from Indonesia. The numeratus group is mainly characterized by a remarkable trait, a pronounced hump between prostheca and mola of the right mandible (Figs 31b, 33b; see also Müller-Liebenau 1984a: fig. 11e; Shi and Tong 2014: fig. 24). A similar hump is present in Offadens soror (Ulmer) and Offadens sobrinus Lugo-Ortiz and McCafferty, but less pronounced. However, other characters such as the stick-like right prostheca and the missing tuft on the medial lobe of the hypopharynx differentiate them from the numeratus group and from Labiobaetis (Suter 1986, Fig. 21;Lugo-Ortiz and Mc-Cafferty 1998, Webb and Suter 2011, Shi and Tong 2014. Among the other Oriental species outside Indonesia and adjacent countries, L. mustus (Kang and Yang) from Taiwan cannot be assigned to any species group. It is mainly characterized by a notch at segment II of the maxillary palp. The setae of the submarginal arc on the dorsal surface of the labrum are of the same type as in the species of the balkei group from New Guinea (spatulate with pronounced apical pectination), but the labial palp segment II is thumb-like and not lobed as in the balkei group and it has a well-developed antennal scape process Yang 1996, Kaltenbach and. Labiobaetis ancoralis Shi and Tong from China is also not similar to any of the species groups or described species. It shares the type of setae of the submarginal arc on the dorsal surface of the labrum with L. mustus (spatulate with apical pectination) and the balkei group from New Guinea, but has, amongst other differences, well developed hindwing pads (Shi and Tong 2014).
Concerning the species from India and Sri Lanka, L. ordinatus (Müller-Liebenau and Hubbard) shares the pronounced hump between prostheca and mola of the right mandible and all other characters of the numeratus group (setae of the submarginal arc on the dorsal surface of the labrum simple, thumb-like protuberance of labial palp segment II, absence of scape process, six pairs of gills, minute hindwing pads) and, therefore, probably belongs to this group. The species is easily differentiated from the other species of that group by the distinctive spines (triangular, some very long, sharply pointed) at the posterior margin of the terga and other characters (Figs 31-34;Hubbard 1985: figs 7, 24, Shi andTong 2014). Labiobaetis geminatus (Müller-Liebenau and Hubbard) is part of the sumigarensis group. The species is differentiated from the other species of this group by its combination of characters: the shape of the protuberance at labial palp segment II, the reduced number of setae forming the submarginal arc on the dorsal surface of the labrum (ca. 12), the shape of maxillary palp segment II, tarsus ventrally without pectinate setae (Figs 16-25;Hubbard 1985: figs 5, 22, Shi andTong 2014).
Labiobaetis jacobusi Kubendran and Balasubramanian has all characters of the sumigarensis group and most certainly belongs to it. The differences to the other species of the group are based on several characters, especially the number of setae forming the submarginal arc on the dorsal surface of the labrum (only ca. 12 in L. jacobusi), the tuft of stout setae at the medial lobe of the hypopharynx (long in L. jacobusi), the number of setae at the dorsal margin of the femur (only ca. seven in L. jacobusi), the shape of the paraproct and the shape of the labial palp (Figs 16-25; Kubendran et al. 2015: figs 42-53). Labiobaetis pulchellus (Müller-Liebenau and Hubbard) cannot be assigned to any of the groups based on its combination of characters. However, the species presents morphological similarities with L. multus. Differences between both are the shape of the labial palps, the dorsal setation of the legs, and the setae at the apex of the mola of the left mandible (present in L. multus, absent in L. pulchellus) (Müller-Liebenau 1984a: fig. 9; Müller-Liebenau and Hubbard 1985: fig. 6).
Labiobaetis soldani Kubendran et al. from India cannot be assigned to a species group because of its combination of characters and is clearly differentiated from all other species (Kubendran et al. 2014).
As a whole, the new species confirm the remarkable morphological differences between the species from Southeast Asia and New Guinea. In New Guinea there are no species with an antennal scape process, all but one species have only six pairs of gills, and there are no species with hindwing pads. In Southeast Asia as well as in other regions, these character states are more evenly distributed and there are at least several species with or without an antennal scape process, with six or seven pairs of gills, and with or without hindwing pads. The main types of setae of the submarginal arc on the dorsal surface of the labrum (simple, feathered, clavate) are almost equally represented in the Oriental realm, whereas the simple type is largely dominant in New Guinea and the feathered type prevailing in the Afrotropical region (Lugo-Ortiz and McCafferty 1997, Gattolliat 2001. Additionally, the species from Southeast Asia have tendentially a limited number of setae at the dorsal margin of the femur (usually fewer than 20 and often fewer than 12 setae), whereas the species from New Guinea have tendentially a high number of these setae (the majority of species have more than 20 setae, sometimes even more than 40, but only in one case fewer than 12). Interestingly, L. seramensis sp. nov. and L. wahai sp. nov. from Seram (both forming the seramensis group) have a closer morphological similarity with the species from New Guinea, especially with the species of the claudiae group, than with the other species from Indonesia. They have simple setae forming the submarginal arc on the dorsal surface of the labrum, no antennal scape process, six pairs of gills and no hindwing pads like the vast majority of species from New Guinea. Additionally, they both have more than 20 setae at the dorsal margin of the femur like the majority of species from New Guinea. These characters together with the geographical proximity of Seram to New Guinea points to an eventual colonization of Seram from New Guinea.
From the 16 species of Labiobaetis (or previously assigned to Pseudocloeon) only known at the imaginal stage, four were described from Indonesia (P. fulmeki Ulmer, P. necopinatum Müller-Liebenau, P. ulmeri Müller-Liebenau from Sumatra, and P. obscurum Ulmer from Java and Sumatra) (Ulmer 1913, 1939, Müller-Liebenau 1981. As the identification of the imaginal stage of Labiobaetis is generally very difficult, we consider it unrealistic to safely associate the larval stage with old type material at the imaginal stage. In this case, rearing material will provide little help. Furthermore, the generic assignment of these species remains questionable in most of the cases. We, therefore, did not take these species into account in our study and wait for an eventual clarification of their status in the future by using ancient DNA methods. In general, the genetic distances between the different species of Labiobaetis are rather high in Indonesia, between 11% and 24% (K2P, Table 3), which is in line with the genetic distances found in New Guinea (avg. 22%; Kaltenbach and Gattolliat 2018). Ball et al. (2005) reported a mean interspecific, congeneric distance of 18% for mayflies from the United States and Canada. There is an exception, L. gueuningi sp. nov. and L. minang sp. nov. have a very low interspecific distance between 1% and 4% (avg. 2.4%). Both species were collected in the same area, but in different altitudes, L. gueuningi sp. nov. between 840 m and 1,300 m and L. minang between 1,640 m and 1,790 m. Despite their clear morphological differences (Figs 26-29), they are morphologically similar to each other and easily distinguishable from other Labiobaetis species by the 3-segmented maxillary palp (Figs 26g, 28g). Their small genetic distance and morphological similarities may reflect a recent speciation event (Ball et al. 2005). Very young species pairs might be difficult to identify using COI, especially if the species have ancestrally polymorphic mitochondrial haplotypes that do not sort according to subsequent speciation events (Funk andOmland 2003, Ball et al 2005). The small interspecific genetic distance could be also the consequence of lower substitution rates in these taxa, the involvement of hybrids or mitochondrial introgression (Ball et al 2005, Dussex et al. 2015, Gattolliat et al. 2016. A very small interspecific distance (K2P 0.8%) was also reported in Gattolliat et al. (2016) for Swiss stoneflies and another case (K2P 2.77%) was reported in Zhou et al. (2010) for a Baetidae species (USA). The collection of both species on different elevation levels points to the direction that elevation could be a driver in their speciation. In the same area (volcano Singgalang in Sumatra), elevation was the only factor found to be driving within-species genetic structuring of two Baetidae species and an important factor for two others (Gueuning et al. 2017).
The intraspecific distances are very low as expected, ranging from 0 % to 2% (K2P). This result is certainly biased as it is based on a limited number of sequenced specimens per species, which were mostly from a single population. But there are two exceptions, L. pilosus sp. nov., where one specimen from another location has an intraspecific distance of 3% to 4%, and L. batakorum sp. nov. with distances of 0% to 4% (avg. 2.5%) between 4 specimens from 3 different locations. Compared to the usual distances between different Labiobaetis species in that region this distance can be still considered as intraspecific. Ball et al. (2005) also reported a case with 6% intraspecific distance in a mayfly in North America and intraspecific K2P distances of more than 3.5% are also not uncommon within Plecoptera (Gill et al. 2015, Gattolliat et al. 2016.
In addition to the 18 new species described in this paper, we obtained two additional COI sequences with clearly interspecific genetic distance to other specimens with similar morphology. In one case, one specimen from Sumbawa cannot be morphologically separated from L. lubu sp. nov. from Sumatra, but the two haplotypes present a K2P distance of 20%. In the other case, one specimen from Sumatra is morphologically identical to L. itineris sp. nov. from Sumbawa and Bali, but with a K2P distance of 12%. Therefore, these have to remain species hypotheses for now without further treatment in this paper. Additional material will be necessary to confirm their status in the future. We also have specimens of five additional undescribed species, which have significant morphological differences to the closest species. Unfortunately, the material is insufficient or partly damaged and we could not extract DNA. We therefore refrain from describing them.
In the majority of cases, the species distribution of Labiobaetis in Indonesia seems to be restricted to a single island (Figs 54, 55), which is fully in line with other Baetidae genera having an insular endemicity close to 100% in the Australasian realm (Gattolliat and Nieto 2009). Exceptions are L. itineris sp. nov. from Bali and Sumbawa, L. weifangae sp. nov. from Sumbawa and Sumba and L. multus from Sumatra and Malaysia, but all these locations are not far away from each other. We consider the distribution of the different species still extremely preliminary, and new sampling may substantially increase the species distribution as it was the case for African and Malagasy representatives of Labiobaetis (Lugo-Ortiz and McCafferty 1997, Gattolliat 2001. Interestingly, for four of the six species described from the Gombak River in Malaysia by Müller-Liebenau (1984a), we describe morphologically similar species from Sumatra: L. roulade sp. nov. (similar to L. difficilis), L. paradiffundus sp. nov. (similar to L. diffundus), L. paranumeratus sp. nov. (similar to L. numeratus), and L. paraoperosus sp. nov. (similar to L. operosus). In the case of L. multus, we were unable to find morphological differences to separate populations from Malaysia and Sumatra. At the opposite, the Afrotropical species L. glaucus (Agnew) presents a widespread distribution reaching from South Africa to Saudi Arabia, even including the Comoros Islands McCafferty 1997, Gattolliat et al. 2018). The species in China have a more widespread distribution as well, and in the case of L. mustus it includes the provinces Hainan and Guangdong, Hong-Kong and even Taiwan (Shi and Tong 2014: fig. 28).
This high level of micro-to meso-endemism restricted to single islands in Indonesia (Figs 54,55) confirms the situation of the genus in New Guinea, where micro-endemism restricted to smaller areas was found as well , and indicates that allopatry could be a major driver of diversity within this genus. The main difference between Indonesia and New Guinea is that Indonesia consists of numerous small to big islands spread over a large area and New Guinea is one large main island with smaller adjacent islands. For New Guinea, large studies on the highly diversified diving beetle genus Exocelina Balke, 1998 (Coleoptera, Dytiscidae) demonstrated allopatry to be the main mechanism of diversification and found strong evidence that recent environmental change in the extremely structured central highlands of New Guinea, with its ongoing formation of rich aquatic resources and remote valleys and mountain blocks, was the primary driver of diversification in that area (Toussaint et al. 2013(Toussaint et al. , 2014. There is also evidence that species in running waters are weaker dispersers than species living in standing water, which has been suggested to promote allopatric speciation and micro-endemism in the first group and dispersal in the second group (Ribera et al. 2001, Monaghan et al. 2005. Labiobaetis species mainly live in running waters, but there are a few exceptions. However, their dispersal ability seems to be high enough to have reached remote islands like Vanuatu (Gattolliat and Staniczek 2011) and Fiji (Flowers 1990) in the past and bidirectional transoceanic dispersal between Madagascar and Africa has been shown as well (Monaghan et al. 2005). Additionally, parthenogenesis has been assumed in the genus, which may favour successful dispersal events (Sivaramakrishnan et al. 1991, Gattolliat andStaniczek 2011).
Despite covering an important part of Indonesia, the sampling effort and the number of localities and different habitats is still extremely limited and there are large areas without any collection activities so far (Fig. 53a). In addition, we have seven species hypotheses based on genetics only or based on morphological differences without genetics, which may be confirmed as separate species in the future. Therefore, we may assume that the number of Labiobaetis species in Indonesia will continue to increase substantially with further collections in the future.