Research Article |
Corresponding author: Thomas Kaltenbach ( thomas.kaltenbach@bluewin.ch ) Academic editor: Ben Price
© 2023 Thomas Kaltenbach, Nikita J. Kluge, Jean-Luc Gattolliat.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kaltenbach T, Kluge NJ, Gattolliat J-L (2023) A new, widespread genus of Baetidae from South Asia (Insecta, Ephemeroptera). ZooKeys 1168: 231-266. https://doi.org/10.3897/zookeys.1168.104844
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Material collected on different islands across South Asia revealed a new genus of Baetidae with a widespread distribution, Arcobaetis gen. nov. The larvae present important similarities with Nigrobaetis, but have paraglossae dorsally with an arc of long, spine-like setae in distal area; long, slightly feathered setae between prostheca and mola of both mandibles; and very slender legs with row of short setae at dorsal margin of femur. The male imago has an extraordinarily small 3rd (apical) segment of gonostylus, which is much narrower than the apex of the 2nd segment. The new genus includes five species: A. sumbawensis sp. nov. is described from Sumbawa (Indonesia) based on larvae, A. sumatrensis sp. nov. from Sumatra (Indonesia) based on larvae, A. bornensis sp. nov. from Borneo (Brunei) based on larvae, and A. sripadai sp. nov. (type species) is described from Sri Lanka based on a reared male imago with its larval and subimaginal exuviae; A. gracilentus (Chang & Yang, 1994), comb. nov. from Taiwan, formerly described in Margobaetis Kang & Yang, 1994, a subgenus of Baetis Leach, 1815, and subsequently transferred to the genus Nigrobaetis Kazlauskas (in Novikova & Kluge), 1987, is transferred to the new genus. A key to the larvae of all species is provided. Morphological similarities and the relationship of the new genus to other genera of Baetidae are discussed.
Brunei, Indonesia, mayflies, Sri Lanka, Taiwan
Baetidae are a highly diverse, cosmopolitan family of mayflies, missing only in New Zealand from among places with mayflies (
Here, we describe and illustrate a new genus of Baetidae, Arcobaetis gen. nov., with a wide distribution across South Asia, including the islands Sumbawa, Sumatra, Borneo, Sri Lanka, and Taiwan. It includes one known species from Taiwan, A. gracilentus comb nov., formerly described in Margobaetis Kang & Yang, 1994, a subgenus of Baetis, and subsequently transferred to the genus Nigrobaetis and now transferred to Arcobaetis gen. nov., and four new species, which are described and illustrated based on larvae (A. sumbawensis sp. nov. from Sumbawa, A. sumatrensis sp. nov. from Sumatra, and A. bornensis from Borneo), and in one case based on a male imago together with its larval and subimaginal exuviae (A. sripadai sp. nov. from Sri Lanka).
The new genus is distinguished from all other genera of Baetidae by the following combination of larval characters: frons with carina-like elevation; both mandibles with long setae between prostheca and mola; paraglossae dorsally with an arc of long, spine-like setae in distal area; very slender legs with femora length 4–6× maximum width; femora with row of short, spine-like setae at dorsal margin; claws with a single row of denticles, distal denticles larger and directed distad, proximal denticles minute; subimaginal gonostyli under cuticle of male last instar larva folded in the “Nigrobaetis-type”. Male imago with an extraordinary small 3rd (apical) segment of gonostylus, much narrower than apex of 2nd segment.
Considering the generally extreme species diversity in South Asia, the rather poor collection activities in the past with the exception of the last two decades, with many still unexplored regions, and the obvious richness of Baetidae in this region, and examination and re-evaluation of historical collections in light of new interpretations, we have to expect further new genera and many more species in the future.
The larvae were collected by kick-sampling and preserved in 70%-96% ethanol. The specimens from Brunei were collected in 2014 by Kate Baker (University of Exeter, UK) during ecological studies in Brunei Darussalam in collaboration with Universiti Brunei Darussalam (
A subimago was reared by one of us (NK) from a mature larva in a glass with stagnant water. Subsequently, the male imago was reared from the subimago in a container with wet air, but without water. The imago was associated with its larval and subimaginal exuviae.
The dissection of larvae was done in Cellosolve (2-Ethoxyethanol) with subsequent mounting on slides with Euparal liquid, using an Olympus SZX7 stereomicroscope. Alternatively, dissection was done in alcohol with subsequent mounting on slides with Canada balsam, using a stereomicroscope MSP 2; and examination with microscope Leica DM 1000.
The DNA of two specimens of one species (A. sumbawensis sp. nov.) was extracted using non-destructive methods allowing subsequent morphological analysis (see
Drawings were made using an Olympus BX43 microscope. To facilitate the determination of species and the comparison of important structures, we partly used a combination of dorsal and ventral aspects in one drawing. Explanations are given in
Photographs of larvae in toto were taken using a Canon EOS 6D camera and processed with the programs Adobe Photoshop Lightroom (http://www.adobe.com) and Helicon Focus v. 5.3 (http://www.heliconsoft.com). Images of larval, subimaginal, and imaginal parts were taken with a DMC 4500 camera on a Leica M205C stereomicroscope, and an Olympus SC 50 camera on an Olympus BX43 microscope, processed with the program Olympus Cell Sense v. 3.2. SEM pictures were taken using a FEI Quanta FEC 250 electron microscope (Thermo Fisher). Photographs were subsequently enhanced with Adobe Photoshop Elements 13.
The distribution maps were generated with the program SimpleMappr (https://simplemappr.net,
The dichotomous key was elaborated with the support of the program DKey v. 1.3.0 (http://drawwing.org/dkey,
The terminology follows
SPbU Saint-Petersburg State University (Russia)
Arcobaetis sripadai sp. nov., by present designation.
Species included in Arcobaetis gen. nov.
1. Arcobaetis sumbawensis sp. nov.
2. Arcobaetis sumatrensis sp. nov.
3. Arcobaetis bornensis sp. nov.
4. Arcobaetis sripadai sp. nov.
5. Arcobaetis gracilentus (Chang & Yang, in
Larva. The following combination of characters differentiate Arcobaetis gen. nov. from all other genera of Baetidae: A) frons with carina-like elevation, slightly overlapping antennal base (Fig.
Arcobaetis sumbawensis sp. nov., larva a labrum (left: ventral view; right: dorsal view) b right mandible c right prostheca d left mandible e left prostheca f hypopharynx and superlinguae g maxilla h labium (left: ventral view; right: dorsal view) i apex of paraglossa (ventral view) j apex of paraglossa (dorsal view).
Larva. Head (Fig.
Labrum
(Fig.
Right mandible
(Fig.
Left mandible
(Fig.
Both mandibles with outer lateral margins almost straight.
Hypopharynx and superlinguae
(Fig.
Maxilla
(Fig.
Labium
(Fig.
Thorax. Legs (Figs
Abdomen. Terga (Fig.
Tergalii. Present on segments I–VII or II–VII.
Paraproct
(Fig.
Larval protogonostyli
(Fig.
Imago. Following combination of characters differentiate Arcobaetis gen. nov. from other genera of Baetidae A) forewing with double intercalary veins (Fig.
Male Imago. See description of male imago under A. sripadai sp. nov. below.
Arcobaetis is a combination of Arco-, in reference to the Latin word arcus for arc and the arc of long, simple setae dorsodistally on paraglossae, and baetis, to highlight the similarities with the genus Baetis. The gender is masculine.
(Fig.
Holotype. Indonesia • male larva (last instar); Sumbawa, Batu Dulang, Mt. Batu Pasak, forest streams; 08°37'42"S, 117°15'27"E, SUMB09; 1380 m; 17.ix.2011; leg. M. Balke; on slide; GBIFCH00975680;
Larva (Table
States of selected larval characters of Arcobaetis gen. nov. Figure numbers refer to those in this paper, while those of A. gracilentus comb. nov. refer to
Characters | A. sumbawensis sp. nov. | Fig. | A. sumatrensis sp. nov. | Fig. | A. bornensis sp. nov. | Fig. | A. sripadai sp. nov. | Fig. | A. gracilentus comb. nov. | Fig. |
---|---|---|---|---|---|---|---|---|---|---|
Sumbawa | Sumatra | Borneo | Sri Lanka | Taiwan | ||||||
Flagellum, enlarged spines on distal margins of segments | absent | absent | present (middle part) | 11f | absent | 14a | absent | |||
Labial palp segment III | sub-rectangular, base approx. as wide as distal margin of segment II | 2h | sub-rectangular, base narrower than distal margin of segment II | 7h | sub-quadrangular, base narrower than distal margin of segment II | 10h | sub-quadrangular, base approx. as wide as distal margin of segment II | 14i | sub-quadrangular, base narrower than distal margin of segment II | 7E |
Hind protoptera | absent | absent | absent | absent | present | 7G | ||||
Tergalii on abdominal segments | I–VII | II–VII | I–VII | II–VII | I–VII | |||||
Abdominal tergite IV, spines on posterior margin | triangular | 3c | triangular | 8i | triangular | 11c | triangular | 15f | triangular | 7K |
slightly wider than long | wider than long | wider than long | slightly wider than long | longer than wide | ||||||
Cerci, spines on outer sides | unknown | two somewhat longer on each 2nd segment | 9f | unknown | several strongly enlarged on each 2nd segment | 15o, p | unknown |
Larva (Figs
Cuticular colouration
(Fig.
Hypodermal colouration.
Abdomen dorsally with narrow reddish transverse stripes on intersegmental membranes (Fig.
Antenna. Flagellum in middle part without enlarged spines at distal margin of segments.
Labrum
(Fig.
Right mandible
(Fig.
Left mandible
(Fig.
Hypopharynx and superlinguae
(Fig.
Maxilla
(Fig.
Labium
(Fig.
Hind protoptera absent.
Legs
(Figs
Abdominal terga
(Fig.
Abdominal sterna.
Posterior margins of sterna: I–V smooth, without spines; VI–IX with triangular spines. On sternum IX of male mature larva row of narrow pointed spines between protogonostyli, smaller spines laterad of protogonostyli and larger, pointed spines laterad of them (similar to Fig.
Tergalii
(Fig.
Paraproct
(Fig.
Caudalii. Cerci and paracercus with broad triangular spines on posterior margin of each segment.
The specific epithet refers to the type locality in Sumbawa (Indonesia).
Indonesia: Sumbawa (Fig.
The species was found at an altitude of 1380 m.
Holotype. Indonesia • female larva (premature); Sumatra Barat, Harau Canyon, stream near Ikbal’s cottage, UN11; 00°06'26"S, 100°40'22"E; 520 m; 23.vi.2012; leg. M. Balke; on slide; GBIFCH00592617;
Larva (Table
Arcobaetis sumatrensis sp. nov., larva a labrum (left: ventral view; right: dorsal view) b right mandible c right prostheca d left mandible e left prostheca f hypopharynx and superlinguae g maxilla h labium (left: ventral view; right: dorsal view) i apex of paraglossa (ventral view) j apex of paraglossa (dorsal view).
Larva (Figs
Cuticular colouration
(Fig.
Hypodermal colouration.
Abdomen dorsally with narrow reddish transverse stripes on intersegmental membranes (Fig.
Antenna. Flagellum in middle part without enlarged spines at distal margin of segments.
Labrum
(Fig.
Right mandible
(Fig.
Left mandible
(Fig.
Hypopharynx and superlinguae
(Fig.
Maxilla
(Fig.
Labium
(Fig.
Hind protoptera absent.
Legs
(Figs
Abdominal terga
(Fig.
Abdominal sterna. Posterior margins of sterna: I–V smooth, without spines; VI–IX with triangular spines.
Tergalii
(Figs
Paraproct
(Fig.
Caudalii
(Fig.
The specific epithet refers to the type locality in Sumatra (Indonesia).
Indonesia: Sumatra (Fig.
The species was found at altitudes of 520 m and 1050 m.
Holotype. Brunei • female larva (premature); Temburong District, Ulu Temburong National Park, near Kuala Belalong Field Studies Centre (KBFSC); 04°32'55"N, 115°09'27"E; 103 m; May 2014; leg. Kate Baker; on slide; GBIFCH00465126;
Larva (Table
Arcobaetis bornensis sp. nov., larva a labrum (left: ventral view; right: dorsal view) b right mandible c right prostheca d left mandible e left prostheca f hypopharynx and superlinguae g maxilla h labium (left: ventral view; right: dorsal view) i apex of paraglossa (ventral view) j apex of paraglossa (dorsal view).
Larva (Figs
Colouration . Head, thorax, and abdomen dorsally brown, ventrally ochre. Legs ecru. Caudalii pale brown.
Hypodermal colouration. Unknown.
Antenna.
Flagellum in middle part with enlarged spines at distal margin of segments (Fig.
Labrum
(Fig.
Right mandible
(Fig.
Left mandible
(Fig.
Hypopharynx and superlinguae
(Fig.
Maxilla
(Fig.
Labium
(Fig.
Hind protoptera absent.
Legs
(Figs
Abdominal terga
(Fig.
Abdominal sternites. Posterior margins of sterna: I–V smooth, without spines; VI–IX with triangular spines.
Tergalii
(Fig.
Paraproct
(Fig.
Caudalii. Spines of cerci and paracercus unknown.
The specific epithet refers to the type locality in Borneo (Brunei).
Brunei (Fig.
(Fig.
Holotype. ♂ imago reared from larva, with its larval and subimaginal exuviae {specimen [XVIII] (5)2020}, Sri Lanka, foot of Sri Pada (Adam’s Peak), Delhausie, river Seetha gangula; 6°50′3.48″N, 80°34′3.36″E; 7.II.2020; leg. N. Kluge & L. Sheyko; SPbU.
Larva (Table
Arcobaetis sripadai sp. nov., larval exuviae a, b fore and middle legs (triangles show points where patella-tibial suture crosses inner margin c claw d–k posterior margins of abdominal terga II–VI and VIII–X l–m posterior margin of abdominal sterna VIII and IX of male larva n paraproct. o–p fragments of cerci (lateral view).
Larva (Figs
Cuticular colouration
(Fig.
Hypodermal colouration. Unknown.
Antenna
(Fig.
Labrum
(Fig.
Right mandible
(Fig.
Left mandible
(Fig.
Hypopharynx and superlinguae
(Fig.
Maxilla
(Fig.
Labium
(Fig.
Hind protoptera absent.
Legs
(Figs
Abdominal terga
(Fig.
Abdominal sterna
(Fig.
Paraproct
(Fig.
Caudalii
(Fig.
Tergalii
(Fig.
Subimago (Figs
Cuticular colouration.
Head and prothorax mostly brown. Mesonotum brown, medioparapsidal suture contrastingly colourless (Figs
Texture. Mesonotum with cross-striated polygonal areas bordered with microtrichia (Fig.
Male imago (Fig.
Genitalia
(Fig.
Dimension. Fore wing length (and body length) 3.5 mm.
Specific epithet refers to the type locality at the foot of the Sri Pada (Adam’s Peak).
Nigrobaetis gracilentus:
Larva. Following combination of characters distinguish Arcobaetis gracilentus comb. nov. from other species of Arcobaetis gen. nov.: A) distal margins of segments in middle part of flagellum without long spines; B) labial palp segment III sub-quadrangular, at base narrower than distal margin of segment II (
Taiwan.
1 | Tergalii present on abdominal segments II-VII | 2 |
– | Tergalii present on abdominal segments I-VII | 3 |
2 | Posterior margin of each 2nd segment of cerci with several enlarged, sharply pointed spines on lateral side (Fig. |
A. sripadai sp. nov. |
– | Posterior margin of each 2nd segment of cerci with two slightly enlarged, pointed spines on lateral side (Fig. |
A. sumatrensis sp. nov. |
3 | Hind protoptera present | A. gracilentus comb. nov. |
– | Hind protoptera absent | 4 |
4 | Flagellum in middle part with enlarged spines at distal margins of segments (Fig. |
A. bornensis sp. nov. |
– | Flagellum in middle part without enlarged spines at distal margins of segments; labial palp segment III sub-rectangular, at base as wide as distal margin of segment II (Fig. |
A. sumbawensis sp. nov. |
The two COI sequences obtained from specimens of A. sumbawensis sp. nov. from the same location have a genetic distance of 0% (K2P), as it is expected in such a case.
The new genus Arcobaetis gen. nov. obviously belongs to the family Baetidae based on the turban eyes of the male imago (Fig.
Based on the rank-free system of Kluge (
The genus Arcobaetis gen. nov. is closely related to Nigrobaetis s.l. (incl. subgenera or genera Nigrobaetis s.str., Takobia Novikova & Kluge, 1987, Alainites Waltz & McCafferty, 1994, Margobaetis Kang & Yang, 1994 and Diphetor Waltz & McCafferty, 1987), sharing several larval characters, e.g., frons with carina-like elevation; labial palp segment II not greatly projected; abdominal terga with scales in trapezoidal nests with corner opercula; subimaginal gonostyli developing under cuticle of last instar male larva folded in “Nigrobaetis-type”. Arcobaetis gen. nov. is distinguished from Nigrobaetis s.l. by paraglossae with a dorsal arc of long, spine-like setae in distal area, and both mandibles with long, slightly feathered setae between prostheca and mola. Nigrobaetis s.l. has no arc of setae on paraglossae and usually has short denticles between prostheca and mola of left mandible or a smooth margin (
The larvae of Procerobaetis Kaltenbach & Gattolliat, 2020, which is another related genus, have remarkable long, pointed tergalii (especially tergalii I and II) (
The male imago of Arcobaetis sripadai sp. nov. has an extraordinarily small 3rd (apical) segment of gonostylus, much narrower than apex of 2nd segment. This is not the case in Nigrobaetis s.l., where the 3rd segment of gonostylus of male imagoes has the usual size, being approx. as wide as the 2nd segment (
Species | Location | Coordinates |
---|---|---|
A. sumbawensis sp. nov | Indonesia: Sumbawa | 08°37'42"S, 117°15'27"E |
A. sumatrensis sp. nov. | Indonesia: Sumatra | 00°06'26"S, 100°40'22"E |
00°56'44"S, 100°32’ 44"E | ||
A. bornensis sp. nov. | Brunei | 04°32'55"N, 115°09'27"E |
A. sripadai sp. nov. | Sri Lanka | 06°50'03"N, 80°34'03"E |
A. gracilentus comb. nov. | Taiwan | 24°28'19"N, 120°58'37"E |
23°32'13"N, 121°31'42"E |
Arcobaetis gen. nov. has a very wide distribution across South Asia, so far including Indonesia (Sumatra, Sumbawa), Brunei (Borneo), Sri Lanka, and Taiwan (Fig.
We sincerely thank Michael Balke (SNSB-Zoologische Staatssammlung München, ZSM, Germany) and Kate Baker (University of Exeter, UK) for the collection of precious material used in this study. Further, we are grateful to Céline Stoffel (
Finally, we are thankful to the reviewers for their valuable comments and corrections.
The authors have declared that no competing interests exist.
No ethical statement was reported.
No funding was reported.
TK: manuscript draft, part of figures; NK: part of manuscript draft, part of figures; J-LG: material assortment, review, discussions.
Thomas Kaltenbach https://orcid.org/0000-0001-8052-0388
Nikita J. Kluge https://orcid.org/0000-0001-9741-7790
Jean-Luc Gattolliat https://orcid.org/0000-0001-5873-5083
All of the data that support the findings of this study are available in the main text or Supplementary Information.