Chydorus reticulatus Daday, 1898

Sinev, Artem Y. & Semenyuk, Irina I., 2021, Males and ephippial females of Oriental Chydoridae (Cladocera: Anomopoda) from Cat Tien National Park, South Vietnam, Zootaxa 4941 (3), pp. 381-398 : 393-394

Chydorus reticulatus Daday, 1898

Uncommon species in Cat Tien ( Sinev & Korovchinsky 2013). Few specimens were found in most samples from localities 1 and 2; single adult male and single ephippial female were found in locality 2 on 05.12.2017. Morphology of parthenogenetic females agrees with its redescription of species ( Michael & Hann 1979; Frey 1982). Ephippial female and male are studied for the first time. Dissection of the male was unsuccessful, and we were able to study distal portion of postabdomen only.

Ephippial female. Body ( Fig. 8A , 9 A–B) globose, similar in shape to that of parthenogenetic female, with highly arched dorsal margin; height-length ratio about 0.92. Ephippium rounded, high, without dorsal keel, with clearly defined ventral margin, covered with distinctive sculpture ( Fig. 9 C–D), same as in parthenogenetic females, consisting of raised polygons, with mesh-like microsculpture inside. Rest of the valve with same sculpture.

Male. Body ( Fig. 8B ) much lower than that of female, irregular oval in lateral view, weakly compressed laterally. Height/length ratio about 0.72, maximum height before midline. Dorsal outline evenly curved, ventral margin of valves unevenly curved. Postero-dorsal angle of valves well-defined, prominent. Valves and head covered with characteristic polygonal sculpture, same as in female. Head with short rostrum, protruding downward and posteriorly. Length of rostrum about 1.5 length of antennule. Rostrum apex blunt ( Fig. 8C ), without denticles at the end. Eye and ocellus of same size as in female.

Postabdomen ( Fig. 8D ) with rather narrow postanal portion, and weakly defined posteroventral angle. Sperm duct openings located laterally at the end of postabdomen above the bases of claws. Ventral margin convex in distal portion. Basis of claws not separated from distal margin. Clusters of 2–3 long setulae in place of postanal marginal denticles. Lateral clusters of setulae same as in female. Postabdominal claw short, curved, with massive basal portion, with two thin basal spines; longer spine about 1/3 length of the claw, short spine two times shorter.A pecten of spinulae on dorsal side of claw.

Size. In single studied ephippial female length was 0.3 mm and height 0.27 mm; in single studied adult male, length was 0.23 mm and height 0.16 mm.

Taxonomic notes. Male postabdomen of C. reticulatus clearly differs from that of other reticulated Chydorus species namely C. invaginatus Frey, 1982 , known from Sri Lanka, and North American C. linguilabris Frey, 1982 (see Frey 1982). It has narrow postanal portion and postanal margin armed with groups of setulae, while in C. invaginatus postanal margin is armed with denticles, similar to those of female, and in C. linguilabris postanal portion is broad, two times higher than in C. reticulatus . In contrast, among closely related species of Chydorus sphaericus complex, any differences between male postabdomens are minimal (Belyaeva & Tailor 2009; Klimovsky & Kotov 2015). Our data differences support Frey’s (1982) opinion of independent evolution of reticulated species of Chydorus .

Figures

FIGURE 8. Chydorus reticulatus Daday, 1898 from locality 2. Ephippial female:A, lateral view.Adult male: B, lateral view; C, rostrum; D, postabdomen.Ephemeroporus barroisi (Richard, 1894) from locality 2.Adult male: E, lateral view; F, posteroventral margin of valves; G, postabdomen; H, antennule and rostrum; I–J, thoracic limb I.

FIGURE 9. Chydorus reticulatus Daday, 1898 from locality 2. Ephippial female (deformed):A, lateral view; B, frontal view; C– D, sculpture of ephippium. Dadaya macrops (Daday, 1898). from locality 6. Ephippial female: E, lateral view; F, ephippium.