Pleuroxus pamirensis (Werestschagin, 1923)

Kotov, Alexey A. & Sheveleva, Natalia G., 2008, Separation of Pleuroxus pamirensis (Werestschagin, 1923) from P. annandalei (Daday, 1908) (Cladocera: Chydoridae), Zootaxa 1775, pp. 25-38 : 32-35

Pleuroxus pamirensis (Werestschagin, 1923)

Figs 5–6

Cornuella pamirensis Werestschagin 1923: 33 -36 (in Russian), 39–40 (in German), Table 2: figs 13–20, Table 3: figs 21– 26; Rylov 1940: 338; Manujlova 1964: 244–245, fig. 129.

Pleuroxus pamirensis (Werestschagin) in Smirnov 1971: 257, figs 259–261; Smirnov 1996: 67 –68 (only Pamirs). Not Pleuroxus pamirensis (Werestschagin) in Smirnov 1996: figs 252–253.

Type series. Type locality. Lake Zorkul, East Pamirs, Tajikistan (altitude: 4138 m, 37º26' N, 73º37' E). In his first description, Werestschagin (1923) stated two localities: "Lake Zor Kul", and "Lake Yashilkul", both from East Pamirs. Smirnov (1971) designated lectotypes from Lake Zorkul and clarified the type locality. Lectotype: Largest adult female (0.71 mm in length) in tube ZIN 1/43533. Unfortunately, this specimen is in a moderately bad state. Paralectotypes. Two adult and one juvenile females. Smirnov (1971, 1996) stated three specimens in this tube, but we found an additional juvenile female.

Additional material examined. Tajikistan, East Pamirs: Few females from a temporary freshwater body NE of Lake Zorkul, coll. in 0 4.08.1959 by A. I. Yankovskaya, NNS 1997-043; female from Lake Yashilkul (altitude: 3700 m, 37º45' N, 72º52' E), coll. in 20.07.1972 by unknown collector, NMK 1080; two females from a pool at E shore of Lake Kara-Kul (altitude: 4000 m, approximately 39º02' N, 73º23' E), coll. in 20.07.1959 by A. I. Yankovskaya, NMK 2302.

Diagnosis. Parthenogenetic female. Body relatively transparent, of moderate height ( Fig. 5 A, D), postero-ventral angle without denticles. No medial keel on dorsum ( Fig. 5 B), valves with paired lateral projections ( Fig. 5 C, E). Rostrum long, protruding ventrally behind apex of labral keel, with a pair of tubercles on tip ( Fig. 5 F, H). Ocellus and compound eye of subequal size. Labral keel relatively small, with broadly rounded apex. Head shield posteriorly rounded, postpore distance = about 1.6 interpore distance. Reticulation obscure, setae at anterior margin lie at a distance from valve edge ( Fig. 6 A); all setae of valve ventral margin exactly marginal ( Fig. 6 C–D), setules on posterior margin of valve exactly marginal. Postabdomen wide, narrowing distally, preanal margin longer than anal margin, preanal and postanal angle well-defined, postanal margin with series of solitary postanal teeth, rarely few teeth from this series supplied with additional, smaller tooth ( Fig. 6 E–F), postabdominal claw with two basal spines of remarkably different size ( Fig. 6 G). Anntenna I relatively thick, not reaching tip of rostrum, with a low basal peg ( Fig. 6 I). On antenna II, all apical "swimming" setae subequal in size, lateral seta on basal segment of endopod shorter than other setae ( Fig. 6 J). Spine on proximal segment of exopod longer than half of next segment length. All thoracic limbs in general as in P. annandalei . On limb I accessory seta present, smallest ODL seta well-defined, distally with minute setules, two largest IDL setae subequal in size ( Fig. 6 K), seta on endite 1 is long ( Fig. 6 L). On inner-distal portion of limb II size of scrapers regularly decreasing basally, filter plate II with eight setae, filter plate III with eight setae, filter plate IV with six setae. Exopodite V without special projections distally to distal seta 1.

Juvenile female with elongated body ( Fig. 5 J), solitary postanal teeth on postabdomen ( Fig. 6 H).

Ephippial female. Unknown.

Male. Described by Werestschagin (1923) inadequately, probably, it has only a single basal spine on postabdominal claw, series of fine setules instead of postanal teeth, three setae of IDL subequal in size.

Size. Lectotype 0.71 mm, parthenogenetic females in our material 0.42–0.74 mm.

Differential diagnosis. See differences from closest P. annandalei in Table 1 .

Distribution. Only described from high mountain lakes and associated pools (altitude:> 3700 m) in Tajikistan, East Pamirs. In pools near Lake Zorkul, P. pamirensis coexists with Pleuroxus n. sp, Dunhevedia cf. crassa King, 1853 , Macrothrix tripectinata Weisig, 1934 , Daphnia magna Straus, 1820 and D. cf. pulex Leydig, 1860 ( Kotov 1999, 2008).

Comments. Werestschagin's (1923) description of Cornuella pamirensis was relatively adequate, and illustrations were quite realistic. Werestschagin (1923) said nothing about differences of his "hornned" animal from Daday's (1908) taxon, because at that time horns in " Euryalona " annandalei were not known.

Figures

FIGURE 5. Pleuroxus pamirensis, parthenogenetic females from Lake Zorkul (type series of Werestchagin, 1923) (A-C, J) and from a temporary freshwater body NE of Lake Zorkul (D-I), East Pamirs. (A-C) Lectotype, lateral, anterior and dorsal view. (D-E) Large adult, lateral and dorsal view. (F) Head, lateral view. (G) Head shield. (H) Tip of rostrum. (I) Dorsal head pores. Scale bars: 0.1 mm.

FIGURE 6. Pleuroxus pamirensis, parthenogenetic females from Lake Zorkul (type series of Werestchagin, 1923) (F, H) and from a temporary freshwater body NE of Lake Zorkul (A-E, G, I-L), East Pamirs. (A) Ventral margin of valve. (B-D) Setae at antero-ventral, middle and postero-ventral portion of valve. (E-F) Postabdomen of adult. (G) Postabdominal claw. (H) Postabdomen of juvenile. (I-J) Antenna I and II of adult. (K) Distal portion of limb I. (L) Limb I, inner view. Scale bars: 0.1 mm.