Diaphanosoma lacustris Kořinek, 1981

Korovchinsky, Nikolai M., Walsh, Elizabeth J. & Smolak, Radoslav, 2017, Diaphanosoma Fischer, 1850 (Crustacea: Cladocera: Sididae) of Lake Turkana (East Africa), with the description of a new species of the genus, Zootaxa 4250 (1), pp. 77-89 : 84

Diaphanosoma lacustris Kořinek, 1981

( Fig. 4 )

Kořinek, 1981: 1119, Fig. 12–18 ( D. birgei lacustris , partim); Korovchinsky, 1987: 741–747, Pl. V–IX; 1992: 39, figs. 185– 190; 2004: 297, Fig. 107.

Diagnosis. Parthenogenetic female. Body conically-rectangular, head comparatively small (34.5–38.8 % of body length), with a protruding dorsal part ( Fig. 4 A) which is sometimes deformed ( Fig. 4 B). Eye (5.2–6.8 % of body length) situated near antero-ventral or ventral head margin. Antennules small of regular type. Swimming antennae comparatively short (60.0–73.8 % of body length), with the upper antennal branch not reaching the posterior valve margin ( Fig. 4 A). The proximal segment of the branch has a conspicuous apical denticle ( Fig. 4 C). Shell comparatively high; valves with more or less high posterior margin bearing a small inner thorn ( Fig. 4 D, 4H). The ventral valve margin has a comparatively narrow, long inflexion with 9–11 long marginal feathered setae without marginal setulae between them, proximal ones implanted submarginally. Postero-ventral valve margins bear 18–37 small, thin, densely situated denticles with thin setulae between every two to six of them ( Fig. 4 F, 4G). Postabdominal claws with three basal spines, proximal one conspicuously smaller than others ( Fig. 4 I). Body length: 0.78–0.98 mm.

Remarks. Specimens from Lake Turkana resemble D. mongolianum in having small number of denticles on postero-ventral valve margins yet all other features (comparatively small head and eye, short swimming antenna, high posterior valve margin) unequivocally characterize them as D. lacustris . The small number of denticles on postero-ventral valve margins may be a result of inter-population morphological variability, particularly due to the small size of individuals. Similar features were found in the specimens from Lake Kinneret ( Israel) and from a Bulgarian reservoir (see Korovchinsky 1987).

Figures

FIGURE 4. Diaphanosoma lacustris Kořinek, Lake Turkana, Kenya. A, general lateral view. B, deformed head. C, distal part of proximal segment of upper two-segmented antennal branch. D, armament of postero-ventral and posterior valve margins. E, ventral valve inflexion. F, G, armament of postero-ventral valve margins. H, inner thorn near posterior valve margin. I, postabdominal claw.