Streptocephalus (Streptocephalus) shinsawbuae, Shu, Shu-Sen, Rogers, D. Christopher, Chen, Xiao-Yong & Sanoamuang, La-orsri, 2018

Shu, Shu-Sen, Rogers, D. Christopher, Chen, Xiao-Yong & Sanoamuang, La-orsri, 2018, Streptocephalus diversity in Myanmar, with description of a new species (Branchiopoda, Anostraca), ZooKeys 734, pp. 1-12 : 2-8

Streptocephalus (Streptocephalus) shinsawbuae sp. n. Figures 1, 2, 3, 4

Holotype.

KIZ–CR 2016001, male, collected from type locality on 29 December 2016: SS Shu, XY Chen, T Qin, KM Myint and TS Tin. Type deposited in the Kunming Natural History Museum of Zoology, Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences (CAS).

Allotype.

KIZ–CR 2016002, female, same data as holotype.

Paratypes.

One male ( SEABRI–CR 2016001) and one female ( SEABRI–CR 2016002) deposited in Freshwater Biodiversity Laboratory, Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences, Myanmar, same data as holotype.

Type locality.

(Fig. 1A, B) Myanmar: Mandalay Region: Pyawbwe Township: near Yanaung Village: a pond in the southern side of the road from Pyawbwe to No. 1 Highway, 20°33 ’46.9” N, 95°58 ’53.70” E, altitude 242 m.

Material examined.

MYANMAR: Mandalay region: Pyawbwe Township: near Yanaung Village: a pond in the southern side of the road from Pyawbwe to NO. 1 Highway, 20°33'46.9"N, 95°58'53.70"E, altitude 242 m, 25 males and 18 females. Zayetkon Township: a pond near the road from Kyaukpadaung to Nay Pyi Taw, 20°48'51.63"N, 95°26'58.88"E, altitude 430 m, 11 males and 24 females. SAGAING REGION: Monywa and Chaung-U Townships: a pond near Bawditataung Nature Reserve (Laykyun Sekkya Buddha), 22°5'26.47"N, 95°16'30.85"E, altitude 141 m, 6 males and 22 females. Myo Thar Township: a pond near the road from Gway Kone to Myo Thar, 21°43'37.31"N, 95°46'40.34"E, altitude 172 m, 15 males and 8 females. MAGWAY REGION: Yesagyo Township: a pond near the road from Yesagyo to Lingadaw, 21°38'46.22"N, 95°10'56.00"E, altitude 90 m, 10 males and 8 females. Htammakauk Township: a pond near the road from East Kan Dwinn to Ohnbin, 21°4'13.33"N, 94°43'21.61"E, altitude 105 m, 4 males and 3 females. Kyuntaw Township: a pond near the road from Ywathitkyi to Htanpinchaung, 21°0'16.17"N, 94°41'18.05"E, altitude 128 m, 15 males and 22 females. Chaung Kauk Township: a pond near the road from Koebin to Egayit, 19°38'22.09"N, 95°20'25.40"E, altitude 153 m, 6 males and 12 females. Lelu Township: a pond near the road from Taungdwingyi to Magway, 20°11'55.78"N, 95°22'0.62"E, altitude 145 m, 15 males and 13 females. Yenangyaung City, Gyae Gone Township: a pond near the road from Gyae Gone to Wetchok, 20°24'31.38"N, 95°2'57.32"E, altitude 200 m, 5 males and 17 fe males. All specimens except the type series were collected by SS Shu, XY Chen, T Qin, P Zaw in June and July, 2017, and the locations are marked in Fig. 2.

Diagnosis.

Streptocephalus shinsawbuae sp. n. is a member of the " S. dichotomus " species group, and can be distinguished from its congeners by the following characters: base of second antenna distal antennomere expanded, subquadrate, basal projection absent; antennal appendage with long peduncle, with one (rarely two) fleshy papilla(e), distal geniculations with 5-7 spines; anterior primary ramus with a digitiform basoposterior spine, ending distally as a triangular, lamellar projection, anterior ramus posterior branch with a subdistal and shallow notch; posterior ramus biramous, posteriolateral branch with two groups of crenulations, posterior primary ramus with two longitudinal rows of spines, distal tenth slightly curved anteriorly; egg with large, basically pentagonal polygons, separated by vertical ridges.

Description.

Male. (Fig. 1C) Body length (from anterior margin of head to posterior margin of telson, not including cercopods) from 14.5 mm to 20.5 mm, average 17.7 mm.

Head round, subcylindrical. Cephalic appendage (Fig. 3D) short, triangular, unbranched, length ~30 % of second antenna proximal antennomere. First antenna filiform, extending beyond second antenna distal antennomere base, apex blunt, bearing three subequal long setae and two short setae. Second antenna (Fig. 3B) extending posteriorly to eighth thoracic segment. Proximal antennomere subcylindrical, length nearly four times width, medial surface smooth, without setae or pulvinus. Distal antennomere 0.9 times as long as proximal antennomere, laterally directed, smooth, curving medially in distal half; apex expanded and rounded to truncate; base expanded, subquadrate (Fig. 4B), basal projection absent.

Antennal appendage (Fig. 3A) with long peduncle (sensu Maeda-Martinez et al. 1995), length 1.6 times second antenna proximal antennomere, subcylindrical, without pulvinus. Peduncle anteromedial surface proximally with one fleshy papilla, half as long as peduncle, bearing a ventrolateral, longitudinal row of 12-14 subequal spines. Length of middle peduncle pseudosegment (between geniculations) more than half peduncle. Antennal appendage peduncle distal geniculations with a lateral longitudinal row of 5-7 spines; spines smooth, acute, with length approx. half of peduncle width. Antennal appendage apical cheliform structure ( “hand” in Maeda-Martínez et al. 1995) strongly developed, with anterior ramus ( “thumb”) and posterior ramus ( “finger”).

Anterior primary ramus (Figure 4A) (the so called “thumb” see Maeda-Martínez et al. 1995) with an anterior, longitudinal, chitinized carina, ending distally as a triangular, lamellar projection, directed distally. Anterior ramus ( “thumb”) posterior branch ( “spur”) smooth, arcuate, recurving posteriorly approx. 80°, with a subdistal, ventral, shallow notch. “Spur” distoventral margin broadly curving into triangular gap. Triangular gap, becoming a narrow, deep cleft between “spur” and anterior ramus ( “thumb”), at least as long as opening width. Anterior ramus ( “thumb”) gently arcuate, curving anteriorly approximately 30°, apex acuminate.

Posterior ramus ( “finger”) biramous and longer than anterior ramus. Posterior margin in lateral view near rami confluence with a shallow emargination. Posterio lateral branch ("lower finger" in Sanoamuang et al. 2000) arcuate, broadly curved to ~160°, with apex bent nearly 90° distally, nearly attaining primary ramus ("upper finger") apex. Posteriolateral branch anterior margin subcrenulate in basal third, crenulate proximally in distal third. Posterior primary ramus ("upper finger") straight, directed distally, subequal in length to peduncle, with distal tenth slightly curved anteriorly. Anterior surface with two longitudinal rows of spines (Fig. 4C). The lateral spine row bears small, wide based spines, from branch confluence to three fourths the length of the ramus. The medial row bears hyaline spines in a series of medial hyaline lamellae, larger than the lateral spines, with tumid bases and aciculate apices. Medial spines increase in size gradually along proximal three fourths, and become more slender and arcuate in distal fourth. Most lamellae developed and connected, with apical half rotating to the medial side of the branch. The medial spine row distal apex ends subdistally on branch.

Labrum large, triangular, middle compress, apex directed posteriorly. Mandible, first and second maxillae as typical for the genus.

Eleven pairs thoracopods, increasing in size from the first pair to the fifth pair, then decreasing posteriorly. The structures of praeepipodites and epipodites typical for genus. Fifth thoracopod endite I and II with closely set, long plumose marginal setae. Endite I submargin with three widely spaced spines, the distal two are single, the proximal one with a basal spinule. Endite II submargin with two closely spaced spines, distal spine short, proximal spine long. Endite III–V with 3, 2, 2 long plumose setae and 2, 2, 1 spine(s), respectively, with small setae in proximal half. Endopodite broad, margin distal half with sparse plumose setae, each with 1-6 basal spinulae. Exopodite linguiform, margins with closely set plumose setae, longest distally, most setae with basal spinule. Epipod oval, without setae and spines, prae-epipod broadly oval, margins with small hooks.

Genital segments smooth, with lateral linguiform outgrowths. Gonopod (Fig. 3C) cylindrical, with a basomedial spiniform outgrowth, bearing four denticles medially. Everted gonopod elongate, distal end expanded, extending to the distal margin of abdominal segment IV, with a lateral, longitudinal row of spines from base to apex.

Abdomen and cercopods as typical for the genus.

Female. Body smaller than male, body length from 14.0 to 17.5 mm, average 15.4 mm (Fig. 1D).

First antennae 2.2 times length of eye plus peduncle and 1.6 times length of second antennae, apex blunt, with three subequal long setae. Second antennae (Fig. 3F) broad, oval, smooth, apex round, margins bearing short sparse setae. Thorax smooth. Thoracopods as in male.

Brood pouch (Fig. 3E) elongate, fusiform, extending to the middle or apex of abdominal segment V in most specimens, less frequently extending to segment IV or segment VI.

Egg (Fig. 4D) subspherical, approx. 200 μm in diameter, with large, basically pentagonal polygons, separated by vertical ridges, polygons approx. 40 μm in diameter, and with broad floors.

Etymology.

The specific epithet shinsawbuae refers to Queen Shin Sawbu (1453-1460) who facilitated more than 50 years of peace in Myanmar.

Ecology.

During the sampling at the type location in June, 2017, the pond had a water temperature of 37.6 °C, a pH of 8.3, conductivity of 117μS/cm, and the dissolved oxygen was 5.9 mg/L. One species of clam shrimp, Cyzicus pilosus Rogers, Thaimuangphol, Saengphan, and Sanoamuang, 2013 was also collected.

Remarks.

Streptocephalus shinsawbuae sp. n. is a member of the " S. dichotomus " species group, which includes S. dichotomus Baird, 1860, S. echinus Bond, 1934, S. longimanus Bond, 1934, S. sahyadriensis Rogers & Padhye, 2014, S. simplex Gurney, 1906, and S. sirindhornae Sanoamuang et al., 2000. This group is separated from all other Streptocephalus in that the posterior ramus (finger) is biramal. Of the six species in this group, S. shinsawbuae sp. n. is readily separated from other congers by the single papilla on the antennal appendage peduncle. Of approximately 120 male specimens of S. shinsawbuae sp. n., only one male from Magway (20°11'55.78"N, 95°22'0.62"E) had two papillae. This papilla in all other species of group is absent, or numbers three or more.

Streptocephalus shinsawbuae sp. n. is most similar to S. sahyadriensis . Both species have two longitudinal rows of spines on the antennal appendage posterior ramus (finger), and the anterior primary ramus (thumb) bears a small basoposterior spine. However, they can be separated by: (1) the shape of the posterior primary ramus (upper finger), which is straight in the proximal nine tenths, with the apex arcing anteriorly in S. shinsawbuae sp. n. vs. arcing distolaterally in the distal third 90° in S. sahyadriensis ; (2) the posterior ramus posteriolateral branch (lower finger) has two groups of crenulations along the anterior margin in S. shinsawbuae sp. n. vs. only one group subdistally in S. sahyadriensis ; (3) the anterior primary ramus apex shoulder is triangularly acute in S. shinsawbuae sp. n. vs. rounded in S. sahyadriensis ; (4) the anterior primary ramus (thumb) basoposterior spine is digitiform in S. shinsawbuae sp. n. vs. triangular in S. sahyadriensis .

Streptocephalus shinsawbuae sp. n. is similar to S. simplex in having unbranched posterior primary ramus (upper finger), and acute anterior primary ramus (shoulder) apex, but they can be separated by: (1) the posterior ramus posteriolateral branch (lower finger) having two crenulated areas along anterior margin in S. shinsawbuae sp. n. vs. smooth in S. simplex ; (2) the anterior primary ramus (shoulder) apex is triangular in S. shinsawbuae sp. n. vs. parallel sided in S. simplex ; (3) anterior primary ramus (thumb) bearing a basal digitiform spine in S. shinsawbuae sp. n. vs. absent in S. simplex .

The eggs of S. shinsawbuae sp. n. have pentagonal polygons, which are very similar to those of both S. echinus and S. longimanus . From S. simplex it can be readily distinguished by the triangle polygons. In addition, the egg ridges are broad and deep in S. shinsawbuae sp. n. vs. narrow and shallow in S. sahyadriensis .