Pleuroxus wittsteini Studer, 1878

Smirnov, Nikolai N., Kotov, Alexey A. & Coronel, Jorge S., 2006, Partial revision of the aduncus-like species of Pleuroxus Baird, 1843 (Chydoridae, Cladocera) from the southern hemisphere with comments on subgeneric differentiation within the genus, Journal of Natural History 40 (27 - 28), pp. 1617-1639 : 1618-1623

Pleuroxus wittsteini Studer, 1878

( Figures 1–23 )

Pleuroxus wittsteini Studer 1878, p 109 , Figure 4a, b ; Rühe 1914, p 51 –53, Figure 18a, b ; Frey 1993b, p 148 –157, Figures 3–49 ; Smirnov 1996, p 43 –44, Figures 134–139; Hollwedel and Dartnall 1998, p 237 –242, Figures 1–3 , Plates 1–6; Pugh et al. 2002, p 1054 (in part).

Pleuroxus aduncus wittsteini Studer in Lofthouse 1967, p 142 (except Macquarie sample); Smith and Sayers 1971, p 363; Kok 1977, p 6.

See some other records in Pugh et al. (2002).

Type material

Apparently lost.

Type locality

‘‘Den zahlreichen Teichen in der Nähe der Station an Betsy Cove an der NW.-Küste’’, Island of Grande Terre, Kerguelen archipelago.

Material

Many parthenogenetic females from ponds 20 and 30 in De Smet (2001) near Port-aux- Français, Island of Grande Terre, Kerguelen archipelago, collected on 5 February 1998 by W. H. De Smet, sample AAK 2002-026-027.

Short diagnosis

Body dark brown, not transparent, no medial keel on dorsum, postero-ventral angle without denticles. Rostrum does not reach apex of labral keel. Head shield posteriorly widely rounded, anteriorly produced as a blunt rostrum, PP51.4–1.8 ID. Head shield and valves with well-expressed reticulation, prominent under valve surface. All setae of valve ventral margin exactly marginal. Setules on posterior margin of valve exactly marginal. Postabdomen short and wide, strongly narrowing distally, with a widely rounded dorsodistal end, its anal margin clearly longer than preanal margin or postanal margin, anal teeth represented as series of small setules. Antenna I not reaching tip of rostrum, with a strong basal peg. On antenna II, one apical seta on both exopod and endopod shorter than other two setae. On limb I smallest ODL seta well-defined, distally with minute setules, two largest IDL setae subequal in size. On inner-distal portion of limb II scrapers 3–5 of subequal size, scrapers 6–7 of subequal size, setules on gnathobase plumose, filter plate II with eight setae. On exopodite III setae 1 and 3 subequal in length, filter plate III with eight setae. On inner portion of limb IV setae 2–4 with robust setules, filter plate IV with six setae. Exopodite V with two projections distally to distal seta 1.

Redescription of parthenogenetic female

See Frey (1993b), morphology of our specimens ( Figures 1–13 ) fully agrees with this redescription.

Description of thoracic limbs

Limb I ( Figures 14, 15 ). Accessory seta, or corm seta in Frey (1993b), present (not represented in Figure 14 , because located on other side of limb corm), ODL relatively small, bears a long seta with naked distal segment and a short seta with short, setulated distal segment. IDL larger than ODL, series of setules; first IDL seta short, naked, second and third IDL setae subequal in size and similarly armed distally with short, fine setules ( Figure 15 ). Endite 3 with three soft posterior setae (a–c) and stiff anterior seta 1 of similar length. Endite 2 with short seta anterior seta d, long setae e and f, and delicate posterior seta 2 armed with minute setules distally. Endite 1 with long, slender posterior setae g–i, a very short seta j, and anterior seta 3 similar to seta 2. Fascicles of thin setules on inner face of limb, plus bunches of longer thicker setules at ventral margin of limb. Two slender ejector hooks of remarkably different size. A short seta, a remnant of maxillar process, on limb base.

Limb II ( Figures 16, 17 ). Exopodite subquadrangular, without a short seta. Inner portion of limb with eight scrapers, 1–2 specially long, 3–5 shorter, subequal in size, 3–8 shorter, also subequal in size. A series of small projections posteriorly to distal setae, and a small sensillum near scraper 4. Distal armature of gnathobase with a bunch of plumose setules, unique for the anomopods, and four setae (1–4). Filter plate II with eight setae, two distal

members subequal in size and shorter than the rest; basalmost seta of filter plate with inflated basal segment.

Limb III ( Figures 18, 19 ). Exopodite sub-rectangular, with four distal setae (1–4), length of setae 1 and 3 equal, and three lateral setae (5–7). Distal endite with three anterior setae ( Figure 19 : 1–3), all with minute setules distally, of them two distal setae (1–2) long, basalmost seta (3) short. Small sensillae near bases of setae 2 and 3. Basal endite with four anterior setae (4–7), slightly increasing in size basally, armed with fine setules distally, small bottle-shaped sensillum near seta 4. On posterior surface, four soft setae (a–d) of similar size, bilaterally armed with sparse, fine setules. Gnathobase not clearly separated from basal endite. Distal armature of gnathobase with large, bottle-shaped sensillum (1), three setae (2–4), and a bunch of setules. Filter plate III with eight setae, distalmost seta shorter than the rest.

Limb IV ( Figures 20, 21 ). Exopodite wide, subovoid, with seven setae of unequal size ( Figure 20 : 1–7). Inner-distal portion of limb IV with four marginal setae ( Figure 21 : 1–4). Distalmost seta (1) stout, with minute setules on distal segment, setae 2–4 with thick basal segments and slender, setulated distal segments, sensillae located near setae 2 and 3. On posterior surface, four soft setae (a–d), Gnathobase well-separated, its distal armature with four setae. Filter plate with six setae.

Limb V ( Figures 22, 23 ). Exopodite large, subovoid, with a single distal seta 1 and three lateral setae (2–4), distally to seta 1 there are two projections bearing long setules. Inner limb portion as elongated, flat lobe, with setulated inner margin, supplied with setulated setae 1 and 2, the latter bears specially robust setules. Distal armature of gnathobase as a single projection, filter plate V with four long setae.

Ephippial female

Unknown.

Male

See Hollwedel and Dartnall (1998).

Size

Females from different localities 0.37–0.77 mm ( Frey 1993b), males 0.55 mm.

Comments

The specimens investigated in the present case fully coincide with figures and description given for P. wittsteini from Kerguelen by Frey (1993b). In the key composed by Frey (1993b) there is a misleading formulation for P. wittsteini : its preanal margin is longer than the anal and postanal margins, which obviously contradicts his drawings (where the anal margin is the longest). In the same key couplet, there is a correct indication for brown P. paraplesius Frey, 1993 that ‘‘both anal and postanal sections much longer than preanal’’. So there is no clear difference in this character (except the fact that in P. wittsteini the anal margin is very wide). In P. paraplesius the postero-ventral angle of the valve is toothed, the shell is not pigmented brown. Our contribution to the study of P. wittsteini is the detailed redescription of its thoracic limbs.

Distribution

Kerguelen archipelago, Heard, Marion, Prince Edward Islands. Pugh et al. (2002) erroneously listed P. scopuliferus among junior synonyms of P. wittsteini and mistakenly referred localities of the former as belonging to the latter.

Figures

Figures 1–11. Pleuroxus wittsteini, parthenogenetic female from ponds near Port-aux-Français, Grande Terre, Iles Kerguelen. (1) Adult in lateral view. (2) Head, lateral view. (3, 4) Head shield and head pores. (5) Anterior half of valve. (6, 7) Armature of antero-ventral and posterior margin of valve. (8, 9) Postabdomen. (10, 11) Its distal portion. Scale bars: 0.1 mm.

Figures 12–23. Pleuroxus wittsteini, parthenogenetic female from ponds near Port-aux-Français, Grande Terre, Iles Kerguelen. (12) Antenna I. (13) Antenna II. (14, 15) Limb I and its inner distal lobe. (16, 17) Limb II and its gnathobase. (18, 19) Limb III and its inner portion. (20, 21) Limb IV and its inner portion. (22, 23) Limb V and its inner portion. Scale bars: 0.1 mm.