Pleuroxus letourneuxi (Richard, 1888)

Kotov, Alexey A. & Ferrari, Frank D., 2010, The taxonomic research of Jules Richard on Cladocera (Crustacea: Branchiopoda) and his collection at the National Museum of Natural History, U. S. A., Zootaxa 2551 (1), pp. 37-64 : 55-58

35. Pleuroxus letourneuxi (Richard, 1888)

Chydorus Letourneuxi Richard 1888b, p. 46 ; Blanchard and Richard 1890, p. 137; Blanchard and Richard 1891, p. 513–

514, figs 1–5; Richard 1894a, p. 376; Gurney 1909, p. 292, Pl. 11: figs 2–23; Gauthier 1928: fig. 44. Pleuroxus obtusirostris Smirnov, 1965 in Smirnov 1966b, p. 339. Pleuroxus letourneuxi (Richard) in Smirnov 1966a, p. 163–167, 176, figs 1–4; Smirnov 1971, p. 254–255, figs 254–257;

Smirnov 1996, p. 61–64, figs 237–242.

Type locality. "une source à Bir-en-Nebech", Tunisia (Richard 1888b) .

Type specimen. NHM 1911.11.8.M.4207, labelled as " Chydorus letourneuxi , Types, Ber-en-Nebeck , Tunis, 1888" .

Richard's specimens in DGF. Many females from sample DGF 962, “Bir en Nebech. Tunisia, M. Letourneux”.

Redescription. Parthenogenetic female. Body transparent, in lateral view rounded, very deep for the genus (body height/ body length = 0.90–0.95 in adults), maximum height in middle ( Fig. 4A, O ). Dorsal margin evenly arched from tip of rostrum to well-defined posterodorsal angle, posterior margin straight, posteroventral angle broadly rounded, without teeth, ventral margin with a distinct prominence in middle. Striation expressed predominantly in anteroventral portions of valve. In anterior view body roundedrhomboid, without a dorsal keel ( Fig. 4B ).

Head with short rostrum, protruding downward ( Fig. 4C ). Eye and ocellus poorly-preserved in Richard’s specimens. Labrum with fleshy main body ( Fig. 4D–E ), small distal labral plate and a large medial labral keel having an elongated apex. Head shield ovoid, maximum width at mid-length, significantly posterior to mandibular articulation, rostrum broadly rounded; posterior margin of head shield also widely rounded ( Fig. 4F–G ). Two major head pores, PP = 1.5–2 IP. Lateral head pores minute located closer to anteriormost pore ( Fig. 4H ).

Valves large, ventral margin armed with numerous setae differing in size in different regions, all plumose and located marginally ( Fig. 4I, K–L ) except for those on anterior margin ( Fig. 4J ). A row of small setules situated on inner side of posterior valve margin close to margin, tips protrude beyond margin ( Fig. 4M–N ).

Postabdomen wide, ventral margin almost straight ( Fig. 5A–D, I ). Preanal margin straight to slightly concave, approximately as long as anal or postanal margin, preanal-postanal angle well-defined, dorso-distal portion of postabdomen widely rounded, withoug distinct depression near base of claws. Each side of postanal portion with successive series of thin postanal teeth, not increasing in size distally, series evenly grading into series of setules on anal margin. Lateral to marginal teeth, two rows of fascicles consisting of short, fine setules. Postabdominal seta shorter than preanal margin, with proximal part longer than distal part. Postabdominal claw short (significantly shorter than preanal or anal margin), massive, slightly and evenly curved, with setules along ventral margin, a spinule distally on its dorsal margin, and two spines toward its base, proximal shorter than distal ( Fig. 5E ).

Antenna I not reaching tip of rostrum, slightly narrowing distally, without a basal peg ( Fig. 5H ). Antennular sensory seta slender, arising on a small prominence at last quarter of antennular length. Nine short aestetascs of slightly differing size. Antenna II relatively short, coxal part with two sensory setae, basis robust, with a rudimentary distal spine ( Fig. 5G ). Antennal branches relatively elongate, exopod and endopod subequal in length, all segments cylindrical, antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Exopod and endopod apical swimming setae subequal in size. No chitinous insertions within distal segments. Lateral seta on proximal segment of endopod thinner and shorter than distal lateral seta. Spine on proximal segment of exopod small.

Paragnath as a shallow, setulated projection. Maxilla I as a projection with three setae ( Fig. 6A )

Limb I ( Fig. 6B ). Accessory seta absent, ODL relatively small, a long, and a short seta both unarmed. IDL approximately as large as ODL, with series of setules; three IDL setae differing in size, similarly armed distally with short, fine setules. Endite 3 with three soft posterior setae (a–c) and somewhat shorter stiff anterior seta 1 ( Fig. 6B : 1). Endite 2 with short anterior seta d, long setae e and f, and thin posterior seta 2 armed with minute setules distally. Endite 1 with long, slender posterior setae g–i, 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 subequal size. A short seta, remnant of maxillar process, on limb base.

Trunk limb II ( Fig. 6C–D ). Exopodite subquadrangular, with a short seta. Inner margin of limb with eight scrapers, 1–2 specially long, 3–5 shorter, subequal in size, 6–8 short, also subequal in size. A series of small projections near distal setae, and a small sensillum near scraper 4. Distal armature of gnathobase with 2 series of thin setules, and four setae (1–4). Filter plate II with eight setae, two ventral elements shorter than the rest; proximal seta of filter plate inflated at base.

Trunk limb III ( Fig. 6E–F ). Exopodite sub-rectangular, with 4 distal setae of different sizes (1–4) and 3 lateral setae (5–7). Distal endite with 3 anterior setae ( Fig. 6F : 1–3), all with minute setules distally; small sensillae near bases of setae 2 and 3. Basal endite with 4 anterior setae of subequal size (4–7), armed with small setules distally, a small bottle-shaped sensillum near seta 4. On posterior surface, 6 setae (a–f) of similar size, bilaterally armed with sparse, fine setules. Gnathobase separated from basal endite. Distal armature of gnathobase with large, bottle-shaped sensillum (1), 3 setae (2–4), plus setules. Filter plate III with 8 setae of similar size.

Trunk limb IV ( Fig. 6G–H ). Exopodite wide, subovoid, with 7 setae of unequal size (1–7). Inner-distal portion of limb IV with 4 marginal setae (1–4),distal seta with minute setules on distal section, setae 2–4 each with thick basal section and slender, setulated distal section, sensillae located near setae 2 and 3. On posterior surface, 4 soft setae (a–d). Gnathobase distinct with 4 distal setae. Filter plate with 6 setae.

Trunk limb V ( Fig. 6I ): Exopodite large, subovoid, with a single distal seta 1 and 3 lateral setae (2–4), distal to seta 1 are 2 small projections bearing long setules. Inner limb portion as elongate, flat lobe, with setulated margins, setae 1 and 2 setulate. Distal armature of gnathobase as a single projection, filter plate V with 4 long setae.

Ephippial female, Male. See Gurney (1909, 1928). The descriptions do not correspond with contemporary level of detail, although the illustrations of the habitus of male and ephippial female ( Gurney 1909, figs. 20, 23) are quite reliable.

Size. Parthenogenetic females 0.33–0.57 mm (in Richard’s specimens), male 0.35 mm ( Smirnov 1996).

Differential diagnosis. Among species of the Pleuroxus with deep body (see Frey 1991; Smirnov 1996; Kotov 2008), P. letournexi is remarkable in its (1) very small size, (2) sub-globular shape, (3) absence on any keel or ridge on dorsal portion of brood chamber and (4) presence of successive series of short, thin postanal teeth as in some other non-globular aduncus -like species (see Frey 1993a; Alonso 1996; Smirnov et al. 2006) and instead of strong singular teeth as in the majority of other sub-globular species. P. letournexi , without a basal peg on antenna I, is another aduncus -like species compromising Frey’s (1993b) intergeneric subdivision of Pleuroxus , as was proposed earlier by Kotov (2008); the size of this peg differs even in some of the closest congeners ( Kotov & Sheveleva 2008). The absence of a basal peg on antenna I in P. letournexi , as well as in few other species ( Smirnov et al. 2006), differentiates these species from the remaining aduncus -like species. P. letournexi has a typical set of filter setae on the gnathobase of limbs II–V (8-8-6-4), which differentiates it from other Pleuroxus -like genera and from a few species of the Pleuroxus (see Frey 1991, 1993a –b; Kotov 2008).

Comments. Valid species, common in the Mediterranean area ( Smirnov 1971, 1996).

Figures

FIGURE 4. Pleuroxus letourneuxi (Richard, 1888), parthenogenetic female from Bir el Nebech, Tunisia, tube DGF 962: (A–B) Adult, lateral and anterior view. (C) Head. (D–E) Labrum, lateral and posterior view. (F–G) Head shield. (H) Dorsal head pores. (I) Valve. (J) Its anterior margin, inner view. (K) Its antero-ventral region. (L) Postero-ventral region. (M–N) Posterior margin of valve, inner view. (O) Juvenile. Scale bars: 0.1 mm

FIGURE 5. Pleuroxus letourneuxi (Richard, 1888), parthenogenetic female from Bir el Nebech, Tunisia, tube DGF 962: (A–B) Postabdomen of adults. (C–D) Its distal portion. (E) Postabdominal claw, external view. (F) Postabdomen of juvenile. (G) Antenna II of adult. (H) Antenna I. Scale bars: 0.1 mm.

FIGURE 6. Pleuroxus letourneuxi (Richard, 1888), appendages of parthenogenetic female from Bir el Nebech, Tunisia, tube DGF 962: (A) Paragnath and maxilla I. (B) Limb I. (C–D) Limb II and distal portion of its gnathobase. (E–F) Limb III and its inner portion. (G–H) Limb IV and its inner portion. (I) Limb V. Scale bars: 0.1 mm.