Camptocercus australis Sars, 1896

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 : 174-179

Camptocercus australis Sars, 1896

( Figs. 3–5 )

Sars 1896: 45–47, figs 9, 10; Smirnov 1971: 436, fig. 531; Smirnov & Timms 1983: 54, fig 63; Smirnov 1998: 71–76, figs 45– 50.

Type locality. The Centennial Park near Sydney, New South Wales, Australia.

Holotype. Parthenogenetic female, Zoological Museum of Oslo University, G. O. Sars collection, F9654

Studied material. Over 30 parthenogenetic females from Australia, North-East Tasmania, Bowlers Lagoon, 14.07.1992, coll. R. Walsh, AAK 2005-052; 17 parthenogenetic females from Australia, Victoria, via Portland, Swan Lake, 38°13' S, 141°19' E, 17.08.1972, coll. B. V. Timms.

Description. Parthenogenetic female. General. Body ( Fig. 3 A–C, 4A, B) with a well-expressed dorsal keel, low oval (height/length ratio about 0.55 in adult), with maximum height at the middle of the body, strongly compressed laterally. Dorsal margin evenly arched, a depression between valves and head shield observed in juveniles of instar I only. Posterodorsal angle broadly rounded; posterior margin convex. Posteroventral angle broadly rounded. Ventral margin from almost straight to irregularly convex, with about 65–75 short ventral setae ( Fig. 3 D); setae in middle and ventral groups rather thick and covered by dense setulae ( Fig. 3 E,F, 4C,D). Row of ventral setae ends at about 3/4 length of ventral margin, followed by numerous very short setulae, subdivided into unclear groups. Posteroventral angle without denticles ( Fig. 3 G). Anteroventral angle rounded. Valves with prominent longitudinal lines, almost never anastomosing. Both valves and head shield covered by fine striae ( Fig. 4 F).

Head ( Fig. 3 H, 4E) with a pointed triangular rostrum, more narrow than in the previous species, protruding downward. Head keel moderately wide; distance from eye to the keel margin about 2–2.5 diameters of eye. Ocellus smaller than compound eye; distance from tip of rostrum to ocellus 2 times greater than distance between ocellus and eye. Three connected major head pores located at the flattened portion of dorsal keel ( Fig. 3 I, 4F–G), connections between pores rather wide, with a line at the middle; PP about 0.5 IP. Lateral pores located at the bottoms of small cavities with thick walls ( Fig. 3 I, 4K), at about 1 IP distance from midline.

Labrum ( Fig. 5 A, B) rather large. Labral keel narrow (height about 1.7–2 widths), with a blunt or rounded apex. Anterior margin of keel convex, posterior margin almost straight, with two clusters of short setulae.

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

Postabdomen ( Fig. 3 J–K, 4H) very long and narrow, evenly narrowing distally, without a defined distal margin. Length of about 4.7–5 heights. Ventral margin straight. Basis of claws elongated, bordered from dorsal margin by a weak incision. Dorsal margin almost straight in postanal portion and weakly concave in anal one, with distal part of about 4.5–5 times longer than preanal one; postanal portion 3–3.5 times longer than anal one. Preanal angle well expressed, but rarely prominent. Postanal angle weakly defined. Preanal margin convex. Postanal margin ( Fig. 3 L, 4I) with 18–20 composite, triangular denticles with narrow, sharp apex and 1–3 small spinules in basal half. Distalmost denticles equal in length to the width of postabdominal claw base. Postanal portion with 14– 17 lateral fascicles of 7–9 setules, much thicker than in the previous species; distalmost setula in each fascicle being longest. Postabdominal claw ( Fig. 3 M, 4J) almost straight, long, about 1.5 lengths of preanal portion of postabdomen, with distinctive pecten of setulae on dorsal margin. Only distalmost element in basal pecten is a spine, equal in length to width of the claw at the spot, all other elements thin, short setulae. Basal spine of usual shape, about 1/4 length of the claw, with several short spinulae on dorsal margin.

Antennule ( Fig. 3 N) long, slightly curved in basal portion, length of about 4.5–5 widths. Anterior face of antennule with three clusters of short setules. Antennular seta as in the previous species. Nine terminal aesthetascs, longest one very thick and significantly longer than antennule, the second longest as long as antennule, other of about 1/3 length of antennule.

Antenna ( Fig. 3 O) similar to that of the previous species, but all spines very short.

Limb I large and massive ( Fig. 5 C,D). Epipodite oval, without projection. Accessory seta very long, about 2/3 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 thin, with a narrow base, with length about 1/3 length of ODL seta. Setae 2 and 3 massive, curved, 1.5 times thicker than ODL seta, with distal portion armed by robust, but not spine-like long setulae; seta 3 about 2/3 length of ODL seta, seta 2 about 1/2 length of seta 3. Endites of similar morphology with the previous species. Ventral face of limb with clusters of short setules. Two ejector hooks, one 1.5 times longer and thicker than other.

Limb II ( Fig. 5 E, F). Exopodite elongated, of irregular shape, with short seta. Eight scraping spines: scrapers 1–2 and 4–5 long, armed with thin setulae; scraper 3 more massive and 1.5 times shorter than neighbors, armed with thick denticles; scrapers 6–8 short, of similar length; 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. 5 G–I). Epipodite oval, without projection. Exopodite of irregular shape, much larger than in the previous species, with seven setae: seta 3 being longest; seta 6 about 1/2 length of seta 3; setae 1, 4 and 7 of similar length, about 1/3 length of seta 3; seta 2 short, seta 5 very short. Seta 3 unilaterally armed with long setulae in basal part and unilaterally (on the opposite side) armed with long setulae in distal part; setae 5–7 naked; seta 4 armed with long thick setulae in distal part, setae 1–2 plumose. Inner portion of limb as in the previous species, but distal endite with seta 3 almost as long as setae 1–2.

Limb IV ( Fig. 5 J–L). Prepipodite setulated; epipodite without projection. Exopodite of irregular shape, with six setae, seta 3 being longest. Setae 5 and 6 of about 2/3 and 1/2 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 similar to that of the previous species, but no inner setae (a–c) found.

Limb V ( Fig. 5 M, N). Prepipodite setulated; epipodite oval, without projection. Exopodite larger than in the previous species, oval, 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 1.5 times longer than basal one. Filter plate with a single seta.

Male and ephippial female unknown.

Size: in studied material, in instar I juvenile female length was 0.52–0.54 mm, height 0.29–0.3 mm; in instar II juvenile female length was 0.63–0.66 mm, height 0.34–0.35 mm, in adult parthenogenetic female length was 0.72– 0.97 mm, height 0.43–0.54 mm.

Differential diagnosis. C. australis presents a unique morphology of lateral head pores within the genus. Also, C. australis differs from C. aloniceps and C. oklahomensis in presence of dorsal keel; from C. lilljeborgi and C. similis in not truncated rostrum; from C. rectirostris , C. fennicus and C. streletskayae in absence of denticles on posteroventral margins of valves and different morphology of IDL setae. Habitually, it is similar to C. uncinatus , C. dadayi and C. vietnamensis , but differs from them by morphology of IDL, with setae 2–3 armed with thin setules, not transformed into any spines; and by specially very long, thin denticles of postabdomen.

Distribution. Australia and Tasmania. According to Smirnov & Timms (1983), it is the only species of Camptocercus present there. All records outside of this region are not reliable.

Figures

FIGURE 3. Camptocercus australis Sars, 1896 from Australia, North-East Tasmania, Bowlers Lagoon. A – B, juvenile females of instar I and II. C – O, parthenogenetic female. C, lateral view. D, ventral margin of valve. E – F, setae from ventral margin of valves of middle and posterior groups. G, posteroventral angle of valves. H, head. I, head pores. J – K, postabdomen. L, distal portion of postabdomen. M, postabdominal claw. N, antennule. O, antenna.

FIGURE 4. Camptocercus australis Sars, 1896, parthenogenetic female from Australia, North-East Tasmania, Bowlers Lagoon. A, lateral view. B, dorsolateral view. C – D, setae from ventral margin of valves of middle and posterior groups. E, head. F, head pores. G, main head pores. H, postabdomen. I, postabdominal claw. J, distal portion of postabdomen. K, lateral head pore.

FIGURE 5. Camptocercus australis Sars, 1896, parthenogenetic female from Australia, North-East Tasmania, Bowlers Lagoon. A – B, labrum. C – N, thoracic limbs. C, limb I. D, IDL and ODL of limb I. E, limb II. F, exopodite of 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, exopodite of limb V. N, inner lobe of limb V.