Pleuroxus quasidenticulatus Smirnov, 1996

Elías-Gutiérrez, Manuel, Kotov, Alexey A. & Garfias-Espejo, Tania, 2006, Cladocera (Crustacea: Ctenopoda, Anomopoda) from southern Mexico, Belize and northern Guatemala, with some biogeographical notes, Zootaxa 1119, pp. 1-27 : 13-14

Pleuroxus quasidenticulatus Smirnov, 1996 ( Figs 26–31 )

Material examined: Five females from Leona Vicario I and one female from Sabancuy ( Mexico).

Body 0.55–0.6 mm, oval, moderately elongate, with a long rostrum. Ventral margin of valves with 60–70 plumose setae ( Fig. 32 ). Posterior margin of valves angulated, with one­two denticles directed posteriad ( Figs. 33, 34 ). Antennule short, with nine aesthetascs and a lateral seta. Labrum triangular, anterior side being convex almost straight ( Fig. 35 ). Second antenna with spine formula: 1–0–1/0–0–1, seta formula: 0–0–3/1–1–3 ( Fig. 36 ). Postabdomen narrowing distally, with anal spines increasing in size distally. Postabdominal claws with proximalmost basal spine smaller than distal one ( Fig. 37 ). Limbs follow arrangement proposed by Chiambeng & Dumont (2004).

Trunk limb I, ODL with a long seta plus a small spine near base; IDL with three setae ( Fig. 39 ); two shorter, unequal in length and one long seta, finely setulated on one side, more robust than the other ones. Corm with five rows of stiff, curved setules on ventral side and 10 long setae ( Fig. 38 ) located on three endites: E1 with three setulated setae of subequal length and an accessory seta; E2 with three setae, the middle one longest; a shorter accessory seta near its base; E3 with four bisegmented bilaterally setulated setae, one of them located below E1. A single seta (maxillary process) and two ejector hooks near base of limb.

Trunk limb II ( Fig. 40 ), EX barrel­shaped, with a broad­based, apically implanted seta. Endopodite with eight scrapers. All scrapers finely denticulated. Scrapers 1–2 the longest, subequal in size; 3–4 decreasing in length, with 5 longer again, and 6­8 shorter, decreasing in length. The part of the GT between scraper 8 and apical elements convex, adorned with tuft of spine­like setae and a distal spinule. Gnathobasic filter­comb with eight setae.

Trunk limb III ( Fig. 41, 42 ), EP squarish, EX rectangular, with three external setae approximately the same length and four distal setae; seta closest to external side thickest and longest; seta 6 with 6–8 stiff, long setules; seta 7 lined with shortened setules. Endopodite ( Fig. 42 ) on external portion with two long setae and one receptor. Internal portion with distal row of four, stiff setae and an obliquely placed receptor. Laterally five bisegmented setae. Posteriorly a comb of six setae.

Trunk limb IV ( Figs. 43, 44 ) with PEP as a lobe marginally feathered with long setules; EP elongate; EX roundish, with seven marginal setae: setae 1–4 subequal; 5–6 shorter, similar in size, and 7 the shortest ( Fig. 43 ); endopodite ( Fig. 44 ) with external erect spine and three setae. A comb of three plumose setae present on its posterior side. Gnathobase with finger­like receptor and a comb of six plumose setae.

Trunk limb V ( Fig. 45, 46 ), PEP marginally feathered; EP elongate, subrectangular; EX with four setae followed by two internal “humps” (sensu Chiambeng & Dumont (2004); EN small, single lobed, elongate, partially setulated and with one seta near its base, much shorter than single long seta on GT; FC with four setae ( Fig. 46 ).

Frey (1993) and later Smirnov (1996b) supported the idea of a separate genus Picripleuroxus , based on the elongate shape of some Pleuroxus ­like chydorids. Later Chiambeng and Dumont (2004), after a careful analysis of thoracic limbs, concluded that the existence of this new genus proposed by Frey (1993) is doubtful. Considering the conservative structure of the limbs in this genus, we coincide at the moment with Chiambeng and Dumont (2004). This species has been recorded in Iraq and Argentina ( Smirnov 1996a). The morphology of our material agrees with Smirnov's (1996b) description, and the species is undoubtedly related to P. denticulatus . From this species it differs in relative length of setae of fifth limb, the denticles in posteroventral corner of valves. However, further revision of South American and Australian populations is needed, as Smirnov (1996a) stated.

Figures

FIGURES 21 – 31. SEM of Grimaldina brazzai, population from Silvituc, Mexico. 21) Lateral view; 22) Head shield, dorso­anterior view; 23) Ventral margin of valve, anterior side; 24) Ventral margin of valve, posterior side; 25) Distal side of postabdomen with claws, lateral view; 26) Proximal side of postabdomen, lateral view; 27) Detail of marginal spines on proximal side of postabdomen; 28) Postabdominal claws, dorsal view; 29) Tip of A 1; 30) A 1, antero­vental view; 31) A 2, endopod and exopod.

FIGURES 32 – 46. Picripleuroxus quasidenticulatus, from Leona Vicario II, Tabasco State, Mexico. Nomenclature of setation pattern follows Chiambeng & Dumont (2004). 32) Lateral view; 33 – 34) Variability of posterior margin of valves; 35 a – b) Variability of labrum shape; 36) A 2, lateral; 37) Postabdomen; 38) Limb I, endites I – III; 39) Limb I, ODL and inner distal lobe IDL; 40) Limb II; 41) Limb III, exopodite and epipodite (GT omitted for simplicity); 42) Limb III, endopodite; 43) Limb IV, exopodite; 44) Limb IV, endopodite; 45) Limb V, endopodite; 46) Limb V, exopodite.