Streblocerus serricaudatus
Creators: name: Tiang-Nga, Supatra
name: Sinev, Artem Y.
name: Sanoamuang, La-Orsri
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Branchiopoda
Diplostraca
Macrothricidae
Streblocerus
Streblocerus serricaudatus

description: Streblocerus cf. serricaudatus (Fischer 1849)
(Figs. 2–4)
Studied material: 3 parthenogenetic females from Lake Kud-Thing (localities 2 and 7; 20 parthenogenetic females from Ban Na-thong Reservoir, Bueng Kan Province, 18°08᾿26.28᾿᾿ N, 103°53᾿38.83᾿᾿ E, 166 m a.s.l.
Description. Parthenogenetic female. General. Length of adult parthenogenetic females is 0.34–0.45 mm. Body sub-oval in lateral view (Figs. 2A, 3 A–B, 4A), maximum height after the middle of body. Dorsal margin convex, postero-dorsal angle well-defined with rounded tip, postero-ventral angle not defined, ventral margin convex with about 15 setae. Valves and head covered with distinctive polygonal sculpture (Fig. 3C). Head relatively large, two times shorter than valves with evenly curved antero-dorsal margin. Major head pore small, round (Fig. 4B). Labrum large, with a distinct keel covered by polygonal sculpture, anterior margin of the keel convex, apex broadly rounded (Figs. 3G, 5D). Compound eye large, ocellus much smaller than an eye.
Antennule (Figs. 3H, 4C) long, strongly curved with four long lateral setae in distal portion. Seven terminal aestetascs, of about 1/3 length of antennule.
Antenna (Fig. 3I) with antennal formula; setae 0-0-1-3/1-1-3, spines 0-1-0-1/0-0-1. The first segment of exopod much smaller than others. Setae of the first and second segment of endopod larger than other setae.
Trunk limb I. Outer distal lobe with one curved seta (Figs. 3J, 4F). Inner distal lobe with 3 curved setae long and curved unequal in size, the largest one with long spines in distal portion (Figs. 3K, 4F).
Postabdomen (Figs. 2B, 3 D–F, 4E) short, with preanal portion 2 times longer than distal (anal+postanal). Ventral margin straight. Dorsal margin bilobed with incursion (but no cleft) between preanal and anal margins. Preanal margin strongly convex with single row of 6–7 large saw-like teeth, increasing in size proximally (Figs. 2B, 3F, 4E). Preanal portion of postabdomen with polygonal sculpture. Postanal angle not defined, distal part of dorsal margin convex. Distal portion of postabdomen without sculpture and about 8 clusters of short setulae. Postabdominal claw as long as distal portion of postabdomen. Basal spine very small. Swimming seta longer than postabdomen with basal and distal portions of similar length, distal portion armed with short setulae.
Taxonomic notes. Streblocerus cf. serricaudatus from Thailand clearly differs from the more common species of SE Asia, S. spinulatus Smirnov 1992, in presence of well-developed saw-like teeth on preanal margin of postabdomen (earlier records of S. spinulatus in Thailand were attributed to S. pygmaeus Sars, 1901 (Maiphae 2008), but it is a South American species (Smirnov 1992). It is obviously different from the African S. inexpectatus Dumont 1981 in the absence of cleft between preanal and anal margins.
Streblocerus serricaudatus s. str. was first described in the vicinity of St. Petersburg, Russia. According to Smirnov (1992), the species was recorded in the Holarctic region, Greenland, Australia, New Zealand and Argentina. Such situation suggests the presence of a species complex, and in our opinion S. cf. serricaudatus from Thailand could be an independent species. Holarctic populations of S. serricaudatus are confined to acid sphagnum bogs with pH 5 or less, but we found S. cf. serricaudatus in neutral or slightly alkaline waters, with pH 6.85–8.58.
Distribution and ecology. In Thailand, S. cf. serricaudatus is a rare species found in only two localities, Lake Kud-Thing and Ban Na-thong Reservoir, Bueng Kan Province. The distance between the localities is about 30 kilometers. Water variables of localities where S. cf. serricaudatus occurred were, temperature 27.1-28.3°C, pH 6.85- 8.58, electric conductivity, 14-19 μS cm-1, total dissolved solid 7-9 mg L-1, and dissolved oxygen 3.15-4.89 mg L-1.
description: Published as part of Tiang-Nga, Supatra, Sinev, Artem Y. & Sanoamuang, La-Orsri, 2020, High diversity of Cladocera (Crustacea: Branchiopoda) in a Ramsar site Lake Kud-Thing, Northeast Thailand, pp. 275-290 in Zootaxa 4780 (2) on pages 280-283, DOI: 10.11646/zootaxa.4780.2.3, http://zenodo.org/record/3842470