﻿First report of the Afrotropical genus Securiops Jacobus, McCafferty & Gattolliat (Ephemeroptera, Baetidae) from Southeast Asia, with description of a new species

﻿Abstract Recent collections in Thailand revealed the occurrence of the genus Securiops in Asia, formerly known from the Afrotropical Realm only. A new species of Securiops is described and illustrated based on larvae and eggs. Eggs of this genus are described for the first time. Morphological differences between the new species and the species from Africa are discussed. The number of species in the genus Securiops is augmented to five.


Introduction
Southeast Asia is one of the regions with the highest diversity worldwide in general, also for mayflies. Much effort has been done in the past years to get a better insight into this yet strongly understudied fauna, including studies of the lesser known, but most diverse mayfly family Baetidae. Emphasis was put on the archipelagos of Indonesia and the Philippines, and continental Thailand. As a result, new genera of Baetidae and many new species were discovered in this region (e.g., Gattolliat 2012;Sutthinun et al. 2018;Suttinun et al. 2020Suttinun et al. , 2021Suttinun et al. , 2022Kaltenbach and Gattolliat 2019;Kaltenbach et al. 2020aKaltenbach et al. , b, 2021Kluge 2020aKluge , b, 2022Suttinun 2021;Phlai-ngam et al. 2022;Tungpairojwong et al. 2022;, and more collection efforts and studies are ongoing. Baetidae are the most diverse family of Ephemeroptera in number of genera (> 118) and number of species (> 1160) worldwide, comprising approximately one third of all mayfly species (Sartori and Brittain 2015;Jacobus et al. 2019;updated by authors). Their distribution is cosmopolitan, with the exception of New Zealand and Antarctica. With continued collections in Southeast Asia and other poorly studied regions with high diversity like New Guinea or the Indian subcontinent, we may expect further new genera and a high number of new species from these regions.
Based on the above-mentioned species, Securiops has a widespread distribution across the Afrotropical region. Here, for the first time, we report the presence of this genus additionally in Southeast Asia, based on the discovery of a new species in Thailand, which is described and illustrated in this study. We also provide the first DNA barcode for Securiops.

Materials and methods
The larvae were collected in 2017 and 2019, and preserved in 70%-96% ethanol.
The dissection of larvae was done in Cellosolve (2-Ethoxyethanol) with subsequent mounting on slides with Euparal liquid, using an Olympus SZX7 stereomicroscope.
The DNA of some 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 and HCO 2198 (Folmer et al. 1994, see Kaltenbach and Gattolliat 2020 for details). Sequencing was done with Sanger's method (Sanger et al. 1977).
GenBank accession numbers are given in the Material examined section. Drawings were made using an Olympus BX43 microscope. Photographs of larvae were taken using a Canon EOS 6D camera and processed with Adobe Photoshop Lightroom v. 5 (http://www.adobe.com) and Helicon Focus v. 5.3 (http://www.heliconsoft.com). Photographs of body parts of the larvae were taken with an Olympus BX43 microscope equipped with an Olympus SC50 camera and processed with Olympus (recently Evident) software Cell Sense v. 1.3. All pictures were subsequently enhanced with Adobe Photoshop Elements 13.

Description. Larva
Colouration . Head, thorax and abdomen dorsally brown, with pattern as in Fig. 1a. Abdomen laterally light brown, with brown spots on most segments (absent or inconspicuous on segments I, IV and X), and larger additional brown spots on segments VI and VIII. Head, thorax and abdomen ventrally light brown, abdomen laterally with brown spots on segments VIII-X (Fig. 1c). Legs light brown, femur with distomedial brown spot, tibia with ventrobasal brown spot, and claw basally darker. Caudalii light brown, with brown annulation at distal margins of segments (Fig. 1a). Labrum (Fig. 2a). Rectangular, length ca. 0.7× maximum width. Distal margin with broad, shallow, medial emargination. Dorsal surface scattered with fine, simple setae; ventral surface with apicolateral patch of long, bifid setae near margin. Anterior margin apicolaterally with row of long, bifid setae, and medially with row of stout, medium, bifid setae.
Right mandible (Fig. 2c, d). Incisor and kinetodontium cleft to base. Incisor with three denticles; kinetodontium with three denticles. Prostheca stick-like, apicolaterally denticulate. With restricted tuft of long setae between prostheca and mola. Tuft of setae at apex of mola present.
Left mandible (Fig. 2e, f ). Incisor and kinetodontium cleft to base. Incisor with three denticles; kinetodontium with four denticles. Prostheca stick-like, apicolaterally denticulate. With large tuft of long setae between prostheca and mola. Tuft of setae at apex of mola present.
Hypopharynx and superlinguae (Fig. 2b). Lingua as long as superlinguae, broad; slightly longer than broad; distal margin almost straight, with fine, simple setae, not forming a medial tuft. Superlinguae distally broadly rounded; lateral margins rounded; fine, medium to long, simple setae along distal margin.
Labium (Fig. 4a-e). Glossa much shorter than paraglossa; outer margin with row of simple setae; inner margin distomedially serrate and with fine, simple setae; ventroapically with arc of long, simple setae. Paraglossa slightly curved inward; outer margin with row of long, simple setae; inner margin with medium row of simple setae, and submarginal row of long, simple setae, basally with dense row of long, simple setae. Labial palp 2-segmented. Segment II large, nearly trapezoidal with distal corner prolonged, pointed, curved inward; inner margin with many long, fine setae, in basal half with submarginal row of long, spine-like, setae-like processes; distal corner with dense, long, fine setae.
Abdominal terga (Fig. 6a, b). Lateral margins of terga: VII with some minute spines; VIII with ca. seven small to large spines; IX with five large spines and one small   spine (spine at posterolateral angle excluded from count); Posterior margins of terga: I smooth, without spines; II with strongly spaced or rudimentary, triangular spines; III-VII with spaced triangular spines, longer than wide.
Tergalii (Fig. 7b). Present on segments I-VII; all tergalii with two lamellae, second lamella much smaller. Tracheae restricted to main trunk. Tergalius I as long as length of segment II; tergalius VII as long as length of segments VIII and half IX combined. Paraproct (Fig. 7a). With four larger, marginal spines, and some additional, minute spines in-between. Cercotractor with minute, marginal spines, hardly to see.
Genetics. We obtained two sequences of 658 bp from specimens of two distinct populations. The K2P distance between them is 0.5%. The closest sequences available on GenBank and Bold system all belong to various species of Cloeon which is to be expected as no specimens of Securiops were previously sequenced.
Etymology. Combination of the first part of the Latin word "prim-us" (meaning the first), and "asia" (for the continent), to highlight the first discovery of the Afrotropical genus Securiops in Asia.
Biological aspects. The specimens were collected at altitudes between 100 m and 300 m. Distribution (Fig. 8)

Differences to Afrotropical species of Securiops
Contrary to the Afrotropical species of Securiops, S. primasia sp. nov. has complete rows of short setae at the dorsal and ventral margins of the femur and tibia, and not just a few setae. Additional to the marginal setation of the legs, S. primasia sp. nov. can be differentiated from the Afrotropical species at least by the following main characters (Lugo-Ortiz and McCafferty 1996;Gattolliat 2003;Jacobus et al. 2006): (1) S. megapalpus with maxillary palp segment I much wider (1.9×) and much longer (2.6×) than segment II (S. primasia sp. nov. with segment I 1.6× width and 1.5× length of segment II); only tergalii I-IV with two lamellae (I-VII in S. primasia sp. nov.); tibia length 1.1× length of claw (1.4× in S. primasia sp. nov.); (2) S. macafertiorum with hind protoptera present (absent in S. primasia sp. nov); abdominal terga V-IX or VI-IX with spines on lateral margins (terga VIII and IX in S. primasia sp. nov.); (3) S. mandrare with spines on lateral margins of abdominal segments IV-IX (VIII and IX in S. primasia sp. nov.); tergalii on abdominal segments I-IV with two lamellae (I-VII in S. primasia sp. nov.); and (4) S. mutadens with spines on lateral margins of abdominal segments IV-IX (VIII and IX in S. primasia sp. nov.); tergalii on abdominal segments I-IV with two lamellae (I-VII in S. primasia sp. nov.).

Eggs
The eggs of this genus are described for the first time. They present similarities with the eggs extracted from subimagos of Baetis alpinus Pictet, 1843, which should be a convergence (Fig. c, d;Kopelke and Müller-Liebenau 1982: fig. 6).

Distribution
The occurrence of Securiops in Southeast Asia in addition to the Afrotropical region, where the four other known species live, is rare for Baetidae as well as for other families of Ephemeroptera. However, apart from the worldwide-distributed genus Cloeon Leach, 1815, there are other examples of Baetidae genera, for example, Labiobaetis Novikova & Kluge, 1987, Nigrobaetis Kazlauskas (in Novikova and Kluge), 1987, Cheleocloeon Wuillot & Gillies, 1993, and Oculogaster Kluge, 2016(Barber-James et al. 2013Kluge 2020a;. The latter belongs to Procloeon s.l. as Securiops (Kluge 2020b). In other families, apart from the worldwide-distributed genus Caenis Stephens, 1835 (Caenidae), there are also genera with a distribution in the Afrotropical region as well as in the Oriental region (and mostly in the Palearctic as well), for example, Ephemera Linné, 1758 (Ephemeridae), Afronurus Lestage, 1924 (Heptagenidae), Euthraulus Barnard, 1932 (Leptophlebiidae), Thraulus Eaton, 1881 (Leptophlebiidae) and Povilla Navás, 1920 (Polymitarcyidae) (Barber-James et al. 2013). However, among the genera mentioned above, only Oculogaster and Cheleocloeon present a discontinuous distribution including exclusively Afrotropical and Oriental realms. Such a distribution pattern could be explained by a stepwise faunal exchange between Africa and Asia via corridors, which probably were more favourable for the dispersal of mayflies during some periods in the past, or by a fauna present on the Indian subcontinent before its drift to the north (Gattolliat and Nieto 2009).
Securiops in continental Africa, Madagascar and Thailand (present study) is rarely collected during standard protocols and freshwater surveys. It may be due to both its scarcity and its ecological requirements (probably partially psammophilous). We may expect that the occurrence of Securiops in Thailand is not an isolated distribution area. More collections in the yet poorly sampled Oriental region may lead to discoveries of a few more new species of Securiops in Southeast Asia, and maybe also on the Indian subcontinent.