Diaphanosoma excisum Sars, 1885

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 : 84-86

Diaphanosoma excisum Sars, 1885

( Fig. 5 )

Sars, 1885: 13–18, Pl. 2, Figs. 1–3 ; Brehm, 1933b: 656–658, Fig. 3 , Taf. 80, Figs. 17–19 ( D. paucispinosum ); Korovchinsky, 1992: 47, Figs. 225–235; 2004: 312, Figs 117, 118, 1, 2; Kořinek, 1984: 36–38, Pl. I–IV.

Diagnosis. Parthenogenetic female. Body conically-rectangular, head of medium size (35.3–38.9 % of body length), rectangular (or may be slightly roundish anteriorly), with a developed dorsal part ( Fig. 5 A, 5B). Eye comparatively large (7.1–8.9 % of body length) and situated close to ventral or antero-ventral head margin. Antennules of regular type. Swimming antennae comparatively long (65.0–81.8 %) but their upper branch not reaching the posterior valve margin. Shell is rectangular with high posterior margin ( Fig. 5 A, 5D), provided with two inner spines of different size (the larger setulated) near it ( Fig. 5 E, 5F). Ventral valve margin with rather wide inflexion joining with postero-ventral margin without a cut and bearing 14–15 long, marginal, feathered setae, proximal of which is smaller and sit submarginally ( Fig. 5 C). Postero-ventral valve margins with 3–12 rather large denticles, numbers of which can vary considerably even between valves of the same individual ( Fig. 5 D, 5G, 5H, 5I, 5J). Basal denticles of postabdominal claws, especially two distal of them, are of almost similar size ( Fig. 5 K). Body length: 0.79–0.90 mm.

Remarks. African representatives of this species have been described only with respect to few features: length of swimming antennae and armament of postabdomen and postero-ventral valve margin (e.g., Weltner 1896; Daday 1910; Brehm 1913; Werestschagin 1915; Delachaux 1917). More recently, comparatively more detailed descriptions have been provided by Kořinek (1984) and Guo & Dumont (2014). The specimens from Lake Turkana referred here are characterized by a moderate body size, relatively large eye, and long swimming antennae ( Table 1 , Fig. 5 ) though the latter not reaching the posterior valve margin. Generally, their morphological variability falls within the range known for the species.

Figures

FIGURE 1. Map of the sampling localities.

FIGURE 2. Diaphanosoma turkanae sp. nov., Lake Turkana, Kenya. A, general lateral view. B, C, D, variation of head shape. E, antennule. F, basipodital distal outer end. G, distal end of proximal segment of upper antennal branch. H, distal end of distal segment of the same branch. I, branches of swimming antenna. J, upper antennal branch. K, shell, dorsal view. L, structure and armament of valve margin. M, structure and armament of posterior and postero-ventral valve margin. N, O, P, armament of postero-ventral valve margin.

FIGURE 3. Diaphanosoma turkanae sp. nov,. Lake Turkana, Kenya. A, B, postabdomen, lateral view. C, postabdominal claw. D, ventral valve inflexion. E, thoracic limb of first pair (tl I). F, distal end of exopodite of tl I. G, thoracic limb of second pair (tl II). H, exopodite of thoracic limb of sixth pair (tl VI). I, endopodite and gnathobase of tl VI.

FIGURE 5. Diaphanosoma excisum Sars, Lake Turkana, Kenya. A, general lateral view. B, variation of head shape. C, ventral valve inflexion. D, posterior and postero-ventral valve margins. E, F, inner thorns near posterior valve margin. G, H, I, J, armament of postero-ventral valve margin. K, postabdominal claw.