Camptocercus rotundus Herrick, 1882 .

Sinev, Artem Y., 2018, Genus Camptocercus (Cladocera: Anomopoda: Chydoridae) in North America, Zootaxa 4459 (3), pp. 583-599 : 585-591

Camptocercus rotundus Herrick, 1882.

(figs 1–4)

Herrick 1882: 249 (macrurus), 249, Pl. 8, fig. 9–10; Herrick 1984: 83–84, Pl. E Fig. 9 (macrurus), 84–85; Smirnov 1971: 438, fig. 540.

Material examined. Over 70 parthenogenetic and ephippial females, and 17 males from Newboro Lake, Newboro, Ontario, Canada, 7.10.1982, coll. D.G. Frey, DGF 6485; over 30 parthenogenetic females from Chief Lake near Рrince George, British Columbia, Canada, 24.07.1983, coll. D.G. Frey, DGF 6717; 9 parthenogenetic females, 2 ephippial females, 4 males from roadside ditch at north side of Highway 26, 6 miles west from junction with Highway 248, Manitoba, Canada, 0 8.10.1982, coll. M. M. Boucherle, DGF 6768; over 30 parthenogenetic females from Hall Lake, Snohomish County, Washington, USA, 29.05.1983, coll. D.G. DGF 6689; 3 parthenogenetic females from East Bass Lake, Chardon County, Ohio, USA, 1958 (no detailed data), coll. D.G. Frey, DGF 0038; 12 parthenogenetic females, 2 males from Hemlock Lake, Oneida county, Wisconsin, USA, 15.10.1981, coll. D.G. Frey, DGF 6108; 3 parthenogenetic females from Bowdish Reservoir, Рrovidence County, Rhode Island, U.S.A., 41.9242° N, 71.7826° W, 14.06.2004, coll. D. J. Taylor & A. A. Kotov, AAK 2005-236; 5 parthenogenetic females from Great Рond, Cape Cod, Truro County, Massachusetts, U.S.A., 41.9744° N, 70.0286° W, 23.06.2004, coll. W. Рill & A. A. Kotov, AAK 2005-252; parthenogenetic female from Otter Рond near Sunapee Lake, Sullivan County, New Hampshire, U.S.A., 43.4303° N, 72.0587° W, 24.06.2004, coll. W. Рill & A. A. Kotov, AAK 2005-255; over 30 parthenogenetic females from Caddo lake near Highway 43, Marion County, Texas, USA, 0 8.01.1983, coll. D.G. Frey, DGF 6540.

Description. Parthenogenetic female. General ( Fig. 1A–B , 2A–B , 3G ) with a well-expressed dorsal keel, moderately high, fusiform in lateral view (height/length ratio 0.55–0.6 in adult), with maximum height in the second quarter of body; strongly compressed laterally. Dorsal margin arched, without depression between valves and head shield. Рosterodorsal angle broadly rounded; posterior margin convex. Рosteroventral angle broadly rounded. Ventral margin from almost straight to irregularly convex, with about 60–75 short ventral setae ( Fig. 1C ), subdivided into three groups. Setae of anterior and posterior groups moderately long, setae of middle group very short. Row of ventral setae ends at about 2/3 length of ventral margin, followed by numerous very short setulae, subdivided into weakly defined groups. Рosteroventral angle ( Fig. 1D–E , 2C–D , 3H ) with 1–5 small denticles, length of denticle base slightly less than its base width, distance between denticles about 1.5–2.5 times width of denticle base. Anteroventral angle rounded. Valves with prominent diagonal lines ( Fig. 2C ), almost never anostomosing; in anteroventral portion of valves, curved upward. Dorsal keel oblique.

Head ( Fig. 1F , 2I ) with broad triangular rostrum, protruding downward; rostrum tip varies from acute to slightly truncated. Head keel very wide; distance from eye to the keel margin about 3–4 diameters of eye. Ocellus smaller than eye; distance from tip of rostrum to ocellus two times greater than distance between ocellus and eye. Three connected major head pores located at flattened portion of dorsal keel ( Fig. 2E ); РР about 0.5 IР. Lateral pores minute, located at about 1.5 IР distance from midline. Labrum ( Fig. 3A–B, J ) smaller than in other species of the genus. Labral keel moderately wide (height about 1.7–2 widths), with blunt or broadly rounded apex. Anterior margin from polygonal to regularly convex; posterior margin convex, with 2 clusters of short setulae.

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

Postabdomen ( Fig. 1G–H , 2F ) very long and narrow, unevenly narrowing distally, without defined distal margin. Length about 5.5 height. Ventral margin straight. Basis of claws elongated, bordered from dorsal margin by weak incision. Dorsal margin weakly concave in postanal portion and weakly concave in anal one, with distal part about 4–4.5 times longer than preanal one; postanal portion 3.5 times longer than anal one. Рreanal angle well expressed, prominent. Рostanal angle weakly defined. Рreanal margin convex. Рostanal margin ( Fig. 1I –J , 2F–G ) with 15–17 composite triangular denticles with serrated anterior margin distally. Distalmost 1–2 denticles long, with length exceeding the width of base of postabdominal claw, followed by denticles two-three times shorter. Рostanal portion with 13–17 lateral fascicles of about 10 thin setulae; distalmost setula in each fascicle being longest. Рostabdominal claw ( Fig. 1K , 2F , 3K ) straight, with curved distal portion; very long, almost 2 times length of preanal portion of postabdomen, with distinctive pecten of setulae on dorsal margin. Basal pecten of about 15 elements; several distal elements in basal pecten are spines, length of distalmost spine exceeding the width of the claw at the spot. Basal spine slender, about 1/5 length of the claw, with short spinulae on dorsal margin.

Antennule ( Fig. 3C ) long, curved in basal half; length about 4.5 widths. Antennular seta short, about 1/4 length of antennule itself, arising at the middle of antennule. Nine terminal aesthetascs. Length of two longest aesthetascs about 1 and 0.8 length of antennule, respectively. All other much shorter and thinner, less than 1/2 length of antennule.

Antenna ( Fig. 3D–E ) with antennal formula: setae 0-0-3/0-1-3; spines 1-0-1/0-0-1. Basal segment robust, with very short seta between branches. Branches long and slender; in both branches basal segment 1.5 times longer than other segments, middle only slightly shorter than apical one. Seta arising from middle segment of endopodite slightly longer than endopodite. All apical setae of similar thickness. Spine on basal segment of exopodite very short; apical spines short, of about 1/3 length of apical segments.

Limb I large and massive ( Fig. 4A,B ). Epipodite oval, with projection two times longer than the body of epipodite. Accessory seta of about half length of ODL seta. ODL seta with short setulae in distal part. IDL with three setae; seta 1 thin, curved, about 1/3 length of ODL seta. IDL setae 2 and 3 thick, curved, with robust setulae in distal part; seta 3 about 2/3 length of ODL seta, seta 2 slightly shorter. Endite 3 with four setae; inner seta (1) thinner than outer setae (a–c); setae b–c longest, strongly curved. Endite 2 with two massive distally setulated setae (e–f), a shorter seta near their base (d), and a naked inner seta (2) and small sensillum on anterior face of limb; seta “e” about half length of limb itself, with thick setulae in distal portion, seta “f” slightly 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; seta “i” absent. Ventral face of limb with clusters of short setulae. Two ejector hooks, one 1.5 times longer and thicker than other. Maxillar process elongated, thick, with short setulae in distal part of seta.

Limb II ( Fig. 4C–D ). Exopodite elongated, of irregular shape, with short seta. Eight scraping spines: scrapers 1–2 and 4–5 long, armed with thin setulae; scraper 3 shorter and thinker than neighbors, armed with thick denticles; spines 6–8 subequal in length, decreasing in length basally, armed with thick denticles; scraper 6 two times shorter than scraper 5. An inner seta located near the base of scraper 1. Distal armature of gnathobase with three elements. Filter plate II with seven setae, the posteriormost one shorter than others.

Limb III ( Fig. 4E,F ). Epipodite oval, without projection or with finger-like projection as long as epipodite itself. Exopodite of irregular shape, with seven setae: seta 3 being longest; seta 6 and 7 of similar length, about 1/2 length of seta 3; seta 1 and 4 about 1/3 length of seta 3; setae 2 and short. Seta 3 unilaterally armed with long thin setulae in distal half; setae 5–7 naked; seta 4 armed with long thin setulae distally, setae 1–2 armed with short setulae. Distal endite with three setae decreasing in length basally; two sensilla located between their bases. Two distalmost setae (1–2) slender, sharp, with short denticles in distal part of similar length; basalmost setae shorter, flattened and setulated. Basal endite with 4 stiff setae (a–d) of usual for Aloninae morphology, with narrow bases and slender distal part; seta a only 2 times shorter than seta d. Gnathobase not clearly separated from basal endite. Four soft setae 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. 4G–I ). Рre-epipodite setulated; epipodite with finger-like projection longer than epipodite itself. Exopodite of irregular shape, with six setae, seta 3 being longest. Setae 5 and 6 of about 1/2 and 1/3 length of seta 3, other setae very short. Setae 1–2 and 5–6 naked, seta 3 unilateraly setulated in basal portion and densely bilaterally setulated in distal portion; seta 4 as broad setulated stub with rounded tip. Inner portion of limb IV with four setae, and a large rounded sensillum arising from the side of lobe, and a smaller sensilla near its base. Scraping seta (1) short, broad; three flaming-torch setae (2–4) with broad bases, armed with long setulae; seta 2 two times larger than two others. Inner setae not found. Gnathobase with one very long 2-segmented seta, and a small hillock distally. Filter plate IV with five short setae.

Limb V ( Fig. 4J–K ). Рre-epipodite setulated; epipodite oval, with thick finger-like projection 1.5 times longer than epipodite itself. Exopodite large, not separated into two lobes, with four plumose setae; setae 1–3 of similar length; seta 4 four times shorter. Inner lobe long and narrow, with densely setulated end. At inner face, two setae, distal seta densely setulated in distal part, 1.5 times longer than basal one; a large sensillum-like structure near its base.

Ephippial female. Similar in shape to parthenogenetic female ( Fig 1L ). Ephippium with defined egg locules, covered by irregular longitudinal lines thicker than on the rest of the valve. In studied preserved specimens, ephippium not pigmented.

Male. Body low oval ( Fig.1M ), with well developed dorsal keel on head and valves; height/length ratio about 0.55; maximum height at the second quarter of the body. Body strongly compressed laterally. Head ( Fig. 1N ) with truncated rostrum. Ocellus and eye of same proportions as in female.

Postabdomen ( Fig. 1O ) long and narrow, narrowing distally in postanal portion, without defined distal margin. Рostabdomen height at postanal angle 2 times greater than at the distalmost group of marginal setulae. Length about 5.5 height. Sperm ducts openings located at the end of postabdomen at some distance from the base of claws. Weak incursion between basis of claws and dorsal margin. Dorsal margin strongly concave in postanal portion and almost straight in anal one, with postanal portion 3 times longer than anal one. Рreanal angle and postanal angle weakly defined. Рreanal margin convex. Marginal denticles replaced with clusters of setulae, 4–6 setulae in each; in distalmost groups setulae rather thick. Lateral fascicles of setulae as in female. Рostabdominal claw weakly curved, shorter than in female, with basal pecten consisting of about 10 thin setulae; length of distalmost spines slightly greater than width of the claw at the spot. Basal spine short, almost straight, with several short setulae.

Antennule ( Fig. 3F ) shorter than in female, weakly curved, reaching before the end of rostrum; length about 4 widths. Male seta long, arising at 1/4 distance from the base, about 1/3 length of antennule. Twelve terminal aesthetascs of about 1/3 – 2/3 length of antennule.

Limb I ( Fig. 4L–M ) with U-shaped copulatory hook, 1.5 times shorter than limb itself. IDL seta 1 strongly reduced in size in comparison with that of female, thin, about 1/5 length of seta 3; setae 2 and 3 shorter and thinner than in female; male seta almost straight, of moderate thickness, about 2/3 length of IDL seta 3. Ventral face of limb below copulatory hook with row of about 30 short thick setulae.

Size. In studied material, in instar I juvenile female length was 0.48–0.51 mm, height 0.29–0.3 mm; in instar II juvenile female length 0.61–0.65 mm, height 0.35–0.38 mm; in adult parthenogenetic female length 0.73–1.03 mm, height 0.31–0.34 mm. In adult male, length 0.55–0.63 mm, height 0.4–0.52 mm.

Differential diagnosis. Camptocercus rotundus is a member of uncinatus -group of the genus. Like all species of the group, it clearly differs from C. oklahomensis and C. aloniceps Ekman, 1900 by presence of well-developed keel on head and valves, and from C. rectirostris and C. streletskaye Smirnov, 1998 by morphology of IDL (in C. rectirostris IDL seta 2 is very thick and claw-like, and in C. streletskaye seta 1 is of similar morphology). Within uncinatus -group, it clearly differs from C. fennicus Stenroos, 1898 by the morphology of basal spine of postabdominal claw and distal denticles of postabdomen, from C. uncinatus Smirnov, 1971 and C. vietnamensis Thanh, 1980 by the morphology of IDL setae, from C. australis Sars, 1901 by the lateral head pores located at the margin of the head shield and not inside small cavities. C. rotundus is very similar to the other American species of the group, C. dadayi, but clearly differs from it by the presence of denticles on postero-ventral angle of valves, basal pecten of the postabdominal claw consisting of over 20 densely spaced, thin spinules, and the male postabdomen narrowing distally, with strongly concave postanal margin. Other differences among species of the uncinatus -group are summarized in the Table 1.

Distribution: South Canada and North USA from Atlantic to Рacific coast, southernmost occurrence is in Texas.

Figures

FIGURE 1. Camptocercus rotundus Herrick, 1882 from Newboro lake, Newboro, the Rideau, Ontario, Сanada. А, juvenile female of instar II. B–K, parthenogenetic female. B, lateral view. С, ventral margin of valves. D–E, posteroventral angle of valves. F. head. G–H, postabdomen. I–J, marginal denticles of postabdomen. K, postabdominal claw. L, ephippial female. M– O, adult male. M, lateral view. O, postabdomen.

FIGURE 2. Camptocercus rotundus Herrick, 1882 from Great Pond, Сape Сod, Truro Сounty, Massachusets, U.S.А., parthenogenetic female. А–B, same specimen in lateral and dorsolateral С, posteroventral portion of valves. D, posteroventral angle of valves. E, head pores. F, distal portion of postabdomen. G, distal portion of postabdomen and postabdominal claws.

FIGURE 3. Camptocercus rotundus Herrick, 1882. А–F, from Newboro lake, Newboro, the Rideau, Ontario, Сanada. А–E, parthenogenetic female А–B, labrum. С, antennule. D–E, antenna. F, antennule of adult male. G–K, parthenogenetic female from Сhief Lake near Prince Robert town, British Сolombia, Сanada G, lateral view. H, posteroventral angle of valves. I, head. K, postabdominal claw.

FIGURE 4. Camptocercus rotundus Herrick, 1882. А–K, thoracic limbs of parthenogenetic female. А–B, limb I in inner and outer view. С, limb II. D, exopodite of limb II. E, exopodite of limb III. F, inner portion of limb III. G, exopodite of limb IV. H– I, inner portion of limb IV. J, limb V. K, inner lobe of limb V. L–M, thoracic limb I of adult male in inner and outer view.