Camptocercus streletskayae Smirnov, 1998

Sinev, Artem Y., 2015, Morphology and phylogenetic position of three species of genus Camptocercus Baird, 1843 (Cladocera: Anomopoda: Chydoridae), Zootaxa 4040 (2), pp. 169-186 : 170-174

Camptocercus streletskayae Smirnov, 1998

( Figs. 1–2 )

Smirnov, 1998: 70–71, figs 28–44, Pl. 2.

Type locality. Lake Chaun, the vicinity of Magadan, Eastern Siberia, Russia.

Type material. Holotype. Female at the Natural History Museum, London, United Kingdom, 1997.1753t.

Paratypes. Females at the Natural History Museum, London, United Kingdom, 1997.1754-1761.

Studied material: 2 specimens from the type locality; 3 parthenogenetic females from Russia, Chukotka, a puddle in the region of the Anadyr River, about 65° N, 171° E, coll. E.A. Streletskaya, AAK 1999-048.

Description. Parthenogenetic female. General. Body ( Fig. 1 A) with a well-expressed dorsal keel, moderately high, slightly fusiform in lateral view (height/length ratio about 0.65 in adult), with maximum height anterior to middle of the body, strongly compressed laterally. Dorsal margin highly arched, without a depression between valves and headshield. Posterodorsal angle broadly rounded; posterior margin convex. Posteroventral angle broadly rounded. Ventral margin from almost straight to irregularly convex, with about 55–65 short ventral setae ( Fig. 1 B–C). Row of ventral setae ends at about 3/4 length of ventral margin, followed by numerous very short setules, subdivided into unclear groups. Posteroventral angle ( Fig. 1 D–F) with 2–4 small denticles; specimens could have a different number of denticles on left and right valve, according to Smirnov (1998), some specimens could lack denticles. Length of denticles about width of denticle base; distance between denticles about 2–4 widths of denticle base. Anteroventral angle rounded. Valves with prominent longitudinal lines, rarely anastomosing, according to SEM photos in Smirnov (1998), valves and headshield are covered by fine striae.

Head ( Fig. 1 G) with a sharp triangular rostrum, protruding downward. Head keel wide; distance from eye to the keel margin about 4 diameters of compound eye. Ocellus smaller than eye; distance from tip of rostrum to ocellus 1.5 times greater than distance between ocellus and eye. Three major head pores ( Fig. 1 H) with a narrow connections between them located at the flattened portion of dorsal keel, PP less than 0.5 1 IP. Lateral pores minute, located at about 1 IP distance from midline.

Labrum ( Fig. 2 A, B) rather large. Labral keel moderately narrow (height about 1.5 widths), with a blunt apex. Anterior margin of keel convex, posterior margin almost straight, with a cluster of short setules and a spine.

Thorax and abdomen of similar length. Dorsal surface of middle abdominal segment saddle-shaped. Abdominal joint well-developed.

Postabdomen ( Fig. 1 I, J) very long and narrow, evenly narrowing distally, with a weakly defined distal margin. Length about 5–6 heights. Ventral margin straight. Basis of claws short, bordered from dorsal margin by a clear incision. Dorsal margin almost straight in postanal portion and weakly concave in anal one, with distal part about 4.5–5 times longer than preanal one; postanal portion 3.5 times longer than anal one. Preanal angle well expressed, prominent. Postanal angle weakly defined. Preanal margin weakly concave. Postanal margin with 17–19 single, mostly subrectangular denticles with serrated distal margin. Distalmost denticle ( Fig. 1 K, L) very long, with length about 1.5 widths of postabdominal claw base and two times longer than neighbors. Postanal portion with 15–17 lateral fascicles of about 15 thin setules, distalmost setule in each fascicle being longest. Postabdominal claw ( Fig. 1 M, N) weakly curved, long, about 1.5 lengths of preanal portion of postabdomen, with a distinctive pecten of setules on dorsal margin. Several distal elements in basal pecten are short spines; length of distalmost spine about half width of the claw at the spot. Basal spine of unusual shape, broad, with narrow base and maximum width at 1/ 3 of length; about 1/3 length of the claw, with short spinules on dorsal margin.

Antennule ( Fig. 1 O) long, slightly curved in basal portion base, length about 4–4.5 widths. Anterior face of antennule with 3 clusters of setulae; setulae of basal cluster rather long. Antennular seta short, about 1/3 length of antennule itself, arising at 2/3 distance from the base of antennule from well-defined tubercle. Nine terminal aesthetascs, longest one almost as long as antennule, the second longest of about 2/3 length of antennule, other of about half length of antennule.

Antenna relatively short ( Fig. 1 P). Antennal formula: setae 0–0–3/0–1–3; spines 1–0–1/0–0–1. Basal segment robust, with a very short seta between branches. Branches long and slender; in both branches basal segment 1.5 times longer and thicker than two others, middle segments slightly shorter than apical. Seta arising from middle segment of endopodite of similar size of apical setae. Spine on basal segment of exopodite about 1/3 length of middle segment. Spines on apical segments about 1/3 length of them.

Limb I large and massive ( Fig. 2 C, D). Epipodite oval, with a curved projection 3–4 times longer than epipodite body. Accessory seta long, about half length of ODL seta. ODL seta thick, with short thin setulae in distal portion. IDL with three setae and several clusters of short setulae. IDL seta 1 hook-like, massive and strongly curved, with broad base, with length about 2/3 length of ODL seta. Setae 2 and 3 only slightly thicker than ODL seta, with distal portion armed by thin setulae; seta 3 about 3/4 length of ODL seta, seta 2 about 2/3 length of ODL seta. Endite 3 with four setae; inner seta (1) thinner than outer setae (a–c), setae a–b strongly curved and 1.5 times longer than setae 1 and c. Endite 2 with two massive distally setulated setae (e–f), a shorter seta near their base (d), a naked inner seta (2) and a small sensillae on anterior face of limb; seta “e” about 2/3 length of limb itself, seta “f” only little shorter than seta “e”. Endite 1 with two 2-segmented setae of similar size (g–h), setulated in distal part, and a naked inner seta (3) two times longer than inner seta of endite 2, on anterior face of limb, a small sensillae near its base; seta “i” absent. Ventral face of limb with clusters of short setulae. Two ejector hooks, one slightly longer and thicker than other. Maxillar process elongated, thick, with short setulae in distal part seta.

Limb II ( Fig. 2 E, F). Exopodite elongated, of irregular shape, with seta of about 2/3 length of exopodite. Eight scraping spines: scrapers 1–2 and 4–5 long, armed with thin setules; scraper 3 more massive and 1.5 times shorter than neighbors, armed with thick denticles; spines 6–8 short, decreasing in length and denticle thickness basally, scraper 6 about 2/3 length of scraper 5. An inner seta located near the base of scraper 1. Distal armature of gnathobase with four elements. Filter plate II with seven setae, the posteriormost one much shorter than others.

Limb III ( Fig. 2 G–I). Epipodite oval, with finger-like projection twice longer than epipodite itself. Exopodite subquadrate, with seven setae: seta 3 being longest; seta 6 and 7 of same length, about 1/2 length of seta 3; seta 1 about 1/3 length of seta 3; other setae short, setae 4 and 5 of similar shape and size. Seta 3 armed with long setules in basal part and unilaterally armed with long thin setulae in distal part; setae 6–7 armed with very short setulae; other setae armed with long thin setulae. Distal endite with three setae decreasing in length basally; two sensillae located between their bases. Two distalmost setae (1–2) slender, sharp, of similar length, with long denticles in distal part; basalmost setae much shorter, flattened and setulated. Basal endite with 4 outer setae (a–d) of unusual for Aloninae morphology, with especially wide bases and wide distal part, strongly increasing in length basally; seta “a” 3 times shorter than seta “d”. Gnathobase not clearly separated from basal endite. Four inner setae (4–7) increasing in size basally; a sensillum near the base of distalmost seta. Distal armature of gnathobase with three elements; the first one an elongated, cylindrical sensillum; the second a geniculated seta; the third a short spine. Filter plate with seven setae.

Limb IV ( Fig. 2 J–L). Preepipodite setulated; epipodite with a finger-like projection two times longer than epipodite itself. Exopodite subquadrangular, with six setae, seta 3 being longest. Setae 5 and 6 of about 3/4 and 2/3 length of seta 3, respectively, other setae very short. Setae 1–2 and 5–6 naked, seta 3 and 4 plumose. Inner portion of limb IV with four setae, a large rounded sensillae arising from the side of lobe, and a smaller sensillae near its base. Scraping seta (1) short, broad; three flaming-torch setae (2–4) with broad bases armed with long setulae; seta 2 about 1.5 times wider than two others. Three inner setae (a–c) very short. Gnathobase with a very long 2- segmented setae, a small hillock distally and a sensillum. Filter plate IV with five short setae.

Limb V ( Fig. 2 M). Preepipodite setulated; epipodite oval, with thick finger-like projection 2 times longer than epipodite itself. Exopodite moderately large, not separated into two lobes, with four plumose setae evenly decreasing in length basally; seta 4 three times shorter than seta 1. Inner lobe long and narrow, with densely setulated end. At inner face, two setae densely setulated in distal part, distal seta almost 2 times longer than basal one. Filter plate not found.

Male and ephippial female unknown.

Size: in studied material, length of adult parthenogenetic female was 0.9–1.05 mm, height 0.53–0.64 mm. According to Smirnov (1998), length of holotype (parthenogenetic female) was 1.2 mm.

Differential diagnosis. C. streletskayae clearly differs from all species of the genus with a dorsal keel by morphology of IDL, with (1) extremely massive, hook-like seta 1, and (2) setae 2–3 of moderate thickness, armed with short setulae. Other distinctive characters of C. streletskayae include unusual morphology of the basal spine of postabdominal claw (a similar, but wider spine is present only in C. fennicus ), and large distalmost marginal denticle of postabdomen (present in C. fennicus and C. similis ).

Distribution. North of the Eastern Siberia and Chukotka, Russia.

Figures

FIGURE 1. Camptocercus streletskayae Smirnov, 1998, parthenogenetic female from Russia, Chukotka, a puddle in the region of the Anadyr River. A, lateral view. B – C, ventral margin of valve (posterior and anterior part of same valve). D – F, posteroventral angle of valve. G, head. H, head pores. I – J, postabdomen. K – L, distal portion of postabdomen. M, postabdominal claw. N, basal spine of postabdominal claw. O, antennule. P. antenna.

FIGURE 2. Camptocercus streletskayae Smirnov, 1998, parthenogenetic female from Russia, Chukotka, a puddle in the region of the Anadyr River. A – B, labrum. C – M, thoracic limbs. C, limb I. D, IDL of limb I. E – F, limb II. G, exopodite of limb III. H – I, inner portion of limb III. J, exopodite of limb IV. K – L, inner portion of limb IV. M, limb V.