Celsinotum Frey, 1991

Sinev, Artem Y. & Kotov, Alexey A., 2012, New and rare Aloninae (Cladocera: Anomopoda: Chydoridae) from Indochina, Zootaxa 3334, pp. 1-28 : 15-16

Genus Celsinotum Frey, 1991 emend. nov.

Type species. Celsinotum parooensis Frey, 1991 (see Frey 1991).

Emended generic diagnosis. Female. Large to moderately sized Aloninae : body high, rounded, compressed laterally valves, but not head shield, with well-expressed keel. Dorsal and ventral margins of valves strongly convex, postero-dorsal, postero-ventral and anterior-ventral angles of valves broadly rounded. Postero-ventral angle of valves without denticles.

Head small, triangle-rounded in lateral view; rostrum short, truncated. Eye larger than ocellus. Head shield broad, rostrum from very short to moderately long in dorsal view, but always truncated, posterior margin of head shield straight. Three narrowly connected major head pores of same size. Lateral head pores minute.

Labrum with large, rounded keel, with rounded apex; its posterior margin without any clusters of setules.

Thorax at least 2 times longer than abdomen. Abdomen without abdominal joint, its middle segment not saddle-shaped.

Postabdomen moderately long, narrowing distally. Ventral margin straight. Basis of claws separated from distal margin by clear incision. Distal margin straight or convex, distal angle broadly rounded. Dorsal margin straight in both anal and preanal positions. Preanal angle well-defined to prominent; postanal angle defined. Marginal denticles in clusters, short, never exceeding width of postabdominal claw base. Lateral fascicles of setules numerous, short, of moderate width. Postabdominal claw of moderate size, with basal spine.

Antennule with nine terminal aesthetascs.

Antenna with formula: setae 0-0-3/1-1-3; spines 1-0-1/0-0-1. Seta of the basal endopod segment always reaching beyond the end of endopod. Seta of the middle endopod and segment, and apical setae of same morphology. Spine of basal exopod segment from very small to moderately long, but shorter than middle segment. Spines of apical segments short, always less than half length of these segments.

Five pairs of thoracic limbs. Limb I with accessory seta. ODL with one long seta. IDL with seta 1 strongly reduced, minute, setae 2–3 armed with thin setules. Endite 3 with four setae, Endite 2 with three setae. Endite 1 with two 2–segmented setae, third seta absent or present. No naked seta on anterior faces of endites 2 and 3. Ventral face of limb with rows of thin setules.

Limb II. Exopodite with very short seta or without it. Inner portion of limb with eight non-differentiated scraping spines, no naked seta near the base of scraper 1. Filter plate II with seven setae, two posteriormost setae considerably shorter than others.

Limb III exopodite with six setae, seta 3 being longest; terminal setae (4–6) long. Scrapers of distal endite long and slender. Filter plate III with seven setae.

Limb IV exopodite with six plumose setae; seta 3 being longest. Inner lobe of limb IV with scraping seta, three flaming-torch setae and small cylindrical sensillum. Three short soft setae. Gnathobase with short 2-segmented setae and a blunt process near it. Filter plate IV with five setae.

Limb V exopodite not separated into two lobes, with 4 plumose setae. Inner limb portion as oval lobe. At inner face, two short setae of similar size. Filter plate V of 0–1 setae.

Male. Body of shape similar to female, with dorsal keel. Postabdomen similar to that of female, but less wide; sperm ducts openings located close to the end of postabdomen, in lateral position. Postabdominal claw much shorter than in female. Antennule with numerous lateral and terminal aesthetascs.

Comments. Our study revealed several new, previously undescribed features of “ Alona ” macronyx , including a well-developed keel on the valves. The male was described for the first time. Analysis of morphology shows that the species should be translocated into the genus Celsinotum Frey, 1991 . The diagnosis of the genus is emended, as the original description of Frey (1991) encompasses only three Australian species, but two more species from Brazil were already described subsequently ( Smirnov & Santos-Silva,1995; Sinev & Elmour-Loureiro 2010).