Oxyurella singalensis ( Daday, 1898 )

Sinev, Artem Y. & Sanoamuang, La-Orsri, 2011, Hormonal induction of males as a method for studying tropical cladocerans: description of males of four chydorid species (Cladocera: Anomopoda: Chydoridae), Zootaxa 2826, pp. 45-56 : 47-49

Oxyurella singalensis ( Daday, 1898)

Daday, 1898: 43–45, Fig 20 ( Alonopsis ), 1910: 135–136, Taf. &, Fig. 21–22 ( Alonopsis ); Grochmalski, 1915: 226–227, Taf. 6,

Fig. 8a, b ( Alonopsis lomnicki ); Brehm, 1934: 66, Fig. 12–13 ( Alona gauthieri ), 1953: 336–339, Abb. 103–105 (lindbergi);

Smirnov, 1971: 497, fig 630–632; Idris, 1983: 130–132, fig. 62; Rane, 1984: 665–667, Fig. 1 –6 ( sangramsagari ); Sharma

& Sharma, 1990: 106, Fig. 11–15.

.

Adult and juvenile males of both instars were obtained at the end of experiment.

Description. Male. Length of juvenile male instar I 0.46 mm, of two juvenile instars II 0.48 and 0.50 mm, and of two adult males 0.50 and 0.52 mm. Both juvenile ( Fig. 1 A, D) and adult males ( Fig. 1 G) of similar outline, low oval. Dorsal and posterior margin of valves convex, posteroventral and posterodorsal angles broadly rounded. Ventral margin of valves convex. Rostrum short, pointed downward. Eye two times larger than ocellus; sizes of eye and ocellus does not substantially differ among different instars.

Postabdomen. In juvenile males of instar I similar to that of juvenile female ( Fig. 2 A), with slightly irregular ventral margin, sperm duct openings located before the middle of ventral margin. In juvenile males of instar II ( Fig 2 B), postabdomen becomes thinner in distal part, with not defined preanal angle. Ventral margin irregular, sperm duct openings located at 1/5 length of ventral margin from the end. Armament of postabdomen and postabdominal claw same as in female in both juvenile instars. In adult male ( Fig. 2 C), postabdomen long, evenly narrowing distally, length about 4 times height. Ventral margin straight with clear step in the region of sperm duct openings, about 1/6 length ventral margin from the end of postabdomen. Distal angle rounded, not prominent. Distal part of postabdomen 3 times longer than preanal, postanal portion 2 times longer than anal one. Both postanal and anal margins weakly concave. Postanal angle weakly defined, preanal angle not defined. Single slender denticle, much smaller than these of juvenile instars, and two peculiar spined hillocks located at the end of postanal margin ( Fig. 2 D, E), followed by about 15 clusters of short setules in place of marginal denticles. Lateral fascicles of setules same as in female. Postabdominal claw only slightly shorter than in juvenile instars, of similar morphology, with basal spine about 0.2 length of claw, two smaller denticles located between basal spine and base of claw.

Antennule. In instar I male ( Fig. 1 B) same as in female. In instar II male ( Fig. 1 E) antennule of same proportions as in previous instar, with anlage of male seta about 1/4 length of antennule itself, aesthetascs same as in female. In adult male ( Fig. 1 H) antennule more broad, length/width ratio about 2, with 9 terminal aesthetascs. Male seta long, about 2/3 length of antennule, arising almost at its tip.

Thoracic limb I. In instar I male with short anlage of copulatory hook, IDL same as in female ( Fig. 1 C). In instar II male, copulatory hook curved ( Fig. 1 F). Ventral face of limb with anlage of copulatory brush seta and a row of about 8 short setules below it. IDL with anlage of male seta, seta 1 becomes very small, setae 2 and 3 as in female. In adult male, limb I only a little larger than in previous instar ( Fig. 1 ), copulatory hook U-shaped, small, 2.5 times shorter than limb itself. Copulatory brush present, a cluster of about 30 spaced long setules located near it, above the copulatory brush seta. IDL seta 1 present, very small, setae 2 and 3 subequal in size, smaller and thinner than in juvenile instars, male seta thick, strongly curved, as long as IDL seta 3. Morphology of endites same as in female.

Taxonomic notes. Daday’s (1898) description and drawings of the general view and postabdomen of male were somewhat fanciful. Rane (1984) described the Indian O. sangramsagari , on differences between males in his material and Daday’s (1898) description, but his taxon was recognized as a synonym by Sharma & Sharma (1990). The descriptions of O. singalensis male were incomplete in all of these publications, and quality of drawings poor. Juvenile males remained undescribed. As far as we can see, there are no significant differences between our material and descriptions by Rane (1984) and Sharma & Sharma (1990).

The morphology and postembryonal development of male Oxuyrella singalensis is similar to those of O. tenuicaudis and O. brevicaudis (see Michel & Frey 1983). O. singalensis male differs from these species by shape of postabdomen, which is longer, evenly narrowing, with undefined preanal angle, by strongly curved male seta of limb I and by the presence of clusters of long setules near copulatory brush of limb I. Postembryonal development of male in Oxyurella is similar to that in other genera of the subfamily (see Frey, 1988; Sinev 2000, 2004ab, 2009a; Sinev et al., 2005), and there is no significant deviation from the general pattern of male ontogenesis (see Sinev 2009a).

Figures

FIGURE 1. Oxyurella singalensis Daday 1898, specimens from culture from Loeng Yai reservoir, Khon Kaen area: A – Cinstar I juvenile male: A—lateral view, B—antennule, C—distal portion of thoracic limb I; D – F—instar II juvenile male: Dlateral view, E—antennule, F—thoracic limb I; G – I—adult male: G—lateral view, H—antennule, I—thoracic limb I. Scale bars: 0.1 mm for A, D, G, 0.05 mm for B – C, E – F, H – I.

FIGURE 2. Oxyurella singalensis Daday 1898, specimens from culture from Loeng Yai reservoir, Khon Kaen area: A – Bpostabdomens of instar I and 2 juvenile males; C—postabdomen of adult male; D – E—distal denticles of adult male postabdomen. Scale bars 0.05 mm for A-C, 0.01 mm for D-E.