Camptocercus oklahomensis Mackin , 1930

Sinev, Artem Y., 2014, A comparative morphological analyses of four species of Camptocercus Baird, 1843 (Cladocera: Anomopoda: Chydoridae), Zootaxa 3895 (2), pp. 183-207 : 185-190

Camptocercus oklahomensis Mackin, 1930

( Figs. 1–4 )

Mackin, 1930: 46–51, Fig. 1–3 ; Smirnov, 1998: 80–81, Fig. 75–82.

Material examined. Over 50 parthenogenetic and ephippial females, 13 adult males, 2 instar II juvenile males from USA, Lousiana, Pointe Coupe Parish, roadside ditch about 2 miles north from Highway 190 on Highway 1, at milepost 173. Collection of Prof. D. G. Frey at National Museum of Natural History (Washington DC, USA), general access number 403774, sample number DGF 4630.

Description. Parthenogenetic female. Body ( Fig.1 A,C; 2A,C) without a dorsal keel, low oval in lateral view (height/length ratio from 0.55–0.58 in adult), with maximum height in the second quarter of body, strongly compressed laterally. Dorsal margin convex, without a depression between valves and head shield. Posterodorsal angle rounded, posterior margin convex. Posteroventral angle broadly rounded. Ventral margin from almost straight to irregularly convex, with about 70–85 short ventral setae ( Fig. 1 E, F; 2D). Row of ventral setae ends at about 4/5 length of ventral margin, followed by numerous, very short setules, not divided into clear groups and continued to posteroventral angle ( Fig. 1 G). Anteroventral angle rounded. Valves with prominent sculpture in shape of longitudinal, almost never anostomosing lines, lines in anteroventral portion of valves curved upward.

Head ( Fig. 3 A) without keel, with dorsal ridge only, rostrum Alona -like. Ocellus smaller than eye, distance from tip of rostrum to ocellus equal to distance between ocellus and eye. Head shield ( Fig. 1 D) of typical for Aloninae morphology. Three connected major head pores ( Fig.3 B) located at flattened portion of dorsal ridge, PP about 1 IP. Lateral pores minute, located at little less than 1 IP distance from midline.

Labrum ( Fig. 3 C,D) rather large. Labral keel wide (height about 1.1–1.3 widths), with a blunt or rounded apex. Anterior margin of keel convex, posterior margin weakly convex, without clusters of setules.

Postabdomen ( Fig. 1 H,I; 2E) long and narrow, unevenly narrowing distally; in larger specimens weakly curved in postanal portion, without defined distal margin. Length about 4–4.5 heights. Ventral margin weakly convex. No incursion between basis and dorsal margin. Dorsal margin concave in postanal portion and almost straight in anal one, with distal part about 3.5 times longer than preanal one; postanal portion 2 times longer than anal one. Preanal angle well expressed, prominent, postanal angle weakly defined. Preanal margin convex. Postanal margin ( Fig. 1 J) with 10–12 groups of 3–5 thin, spine-like denticles, in distalmost groups length of longest denticle about 2/3 width of postabdominal claw base. Postanal portion with 11–13 lateral fascicles of 8–10 thin setules; distalmost setula in each fascicle being longest and thicker than others. Postabdominal claw ( Fig. 1 K) straight, with curved distal portion, very long, about 1.5 lengths of preanal portion of postabdomen, with distinctive pecten of setules on dorsal margin. 7–8 distal elements in basal pecten are long spines; length of distalmost spines about 2 claw widths at the spot. Basal spine slender, very short, about 1/7–1/6 length of the claw, with short spinules on dorsal margin.

Antennule ( Fig. 3 E) short for the genus, not reaching the end of the rostrum, length about 2.5 widths. Antennular seta long, about 1/2 length of antennule itself, arising at 2/3 distance from the base. Nine terminal aesthetascs, the longest two about 3/4 length of antennule; all other much shorter and thinner, about 1/3 length of antennule.

Antenna ( Fig. 2 F, 3F) with antennal formula: setae 0-0-3/0-1-3 and spines 1-0-1/0-0-1. Basal segment robust, with very short seta between branches. Branches shorter and robust; in both branches basal segment 1.5 times longer than apical one, middle segment being 2 times shorter than basal segment. Seta arising from middle segment of endopodite longer than endopodite. All apical setae of similar thickness. Spine on basal segment of exopodite about 1/4 length of middle segment. Spines on apical segments about 1/3 length of them.

Limb I large and massive ( Fig. 4 A,B). Epipodite oval, with projection two times longer, than the body of epipodite. Accessory seta short, about 1/3 length of ODL seta. ODL seta with short setules in distal part. IDL with three setae; seta 1 thin, weakly curved, about 1/3 length of ODL seta. IDL setae 2 and 3 of moderate thickness, not hook-like, with robust setules in distal part; seta 3 about 2/3 length of ODL seta, seta 2 slightly shorter. Endite 3 with four setae of similar length, inner seta (1) thinner than outer setae (a–c). Endite 2 with two massive distally setulated setae (e–f), a shorter seta near their base (d), and a naked inner seta (1) and small sensillum on anterior face of limb; seta e almost as long as limb itself, with long setules in distal portion, seta f about 3/4 length of seta e. Endite 1 with two 2-segmented setae of similar size (g–i), 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 j absent. Ventral face of limb with clusters of short setules. Two ejector hooks, one 1.5 times longer and thicker than other. Maxillar process elongated, thick, with short setulae in distal part seta.

Limb II ( Fig. 4 C). Exopodite ( Fig. 4 D) elongated, of irregular shape, without seta. Eight scraping spines: scrapers 1–5 long; scraper 3 slightly shorter than neighbors, with more thick denticles; spines 6–8 subequal in length, two times shorter than scraper 5; denticles of scraper 8 smaller and thinner than which of scrapers 6–7. 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 shorter than others.

Limb III ( Fig. 4 E,F). Epipodite oval, 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 same length, about 1/2 length of seta 3; seta 1 about 1/3 length of seta 3; other setae short. Seta 3 unilaterally armed with long thin setules in distal half; setae 6–7 naked; other setae armed with short setules. Distal endite with three setae decreasing in length basally; two sensillae 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 1.5 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. 4 G,I). Praepipodite setulated; epipodite with finger-like projection as 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 plumose, seta 3 with very thick basal portion and densely setulated distal portion; seta 4 as broad setulated stub with rounded tip; setae 5–6 naked. Inner portion of limb IV with four setae, a large rounded sensillum 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 setules; seta 2 two times larger than two others. Inner setae not found. Gnathobase with one long 2-segmented setae, a small hillock distally and a sensillum. Filter plate IV with five short setae.

Limb V ( Fig. 4 J). Praepipodite 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 same 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. Filter plate not found.

Ephippial female ( Fig. 1 L; 2G,H) with body slightly higher than in parthenogenetic female. Ephippium ( Fig. 2 I) yellow-brown, with sculpture made up thick, inflated, longitudinal lines.

Male. Body lower than in female, fusiform in both juvenile instar II ( Fig. 1 M) and adult ( Fig. 1 O, 2J), without dorsal keel on head and valves; height/length ratio 0.6; maximum height at 1/3 of the length. Body strongly compressed laterally. Head ( Fig. 3 H) similar in shape to that of female. Ocellus and eye of same size as in female.

Postabdomen. In instar II juvenile male ( Fig. 1 N) similar in shape and armament to that of female; sperm ducts opening located at ventral margin of postabdomen.

In adult male ( Fig.1 P), moderately long and narrow, weakly narrowing distally in postanal portion, without defined distal margin. Length about 5 heights. Sperm ducts opening located at the end of postabdomen above the basis of claws. No incursion between basis of claws and dorsal margin. Dorsal margin weakly concave in postanal portion and almost straight in anal one, with postanal portion 1.5 times longer than anal one. Preanal and postanal angles weakly defined. Preanal margin convex. Marginal denticles replaced with clusters of setules, 6–10 setules in each. Lateral fascicles of setules as in female. Postabdominal claw straight, shorter than in female, with basal pecten consisting of 13–15 spines; length of distalmost spines exceeding width of the claw at the spot. Basal spine similar to that of female, but shorter.

Antennule. In instar II juvenile male ( Fig. 3 G) similar to that of female, with short anlage of male seta. In adult male ( Fig. 3 I), shorter than in female, curved in basal portion, not reaching the end of rostrum; length about 5 widths. Male seta long, arising at 2/3 distance from the base, about half length of antennule. Twelve terminal aesthetascs of about 2/3 – 3/4 length of antennule.

Limb I. In instar II male ( Fig. 4 K,L), copulatory hook curved. Ventral face of limb with anlage of copulatory brush seta, a smaller seta above it, and a row of about 15 short setules below it. IDL with anlage of male seta; seta 1 similar to that of female, small; setae 2 and 3 similar to those of female, but thinner. In adult male ( Fig. 4 M,N), with U-shaped copulatory hook, 2 times shorter than limb itself. IDL setae 1–3 strongly reduced in size in comparison with those of female; setae 2 and 3 armed with thin setules; male seta straight, of moderate thickness, as long as IDL seta 2. Ventral face of limb below copulatory hook with numerous short thick setules in several rows.

Size: in instar I juvenile female length 0.39–0.41 mm, height 0.26–0.27 mm. In instar II juvenile female length 0.44–0.48 mm, height 0.28–0.30 mm. In adult females length 0.63–0.82 mm, height 0.38–0.47 mm. In juvenile males of instar II, length 0.43–0.44 mm, height 0.27–0.28 mm. In adult males length 0.47–0.50 mm, height 0.27–0.30 mm.

Notes. Morphology of head pores and thoracic appendages, and ephippial female of C. oklahomensis were studied for the first time.

Figures

FIGURE 1. Camptocercus oklahomensis from USA, Louisiana, Pointe Coupe Parish, roadside ditch about 2 miles north from Highway 190 on Highway 1. A, outline of juvenile female of instar II. B – K, parthenogenetic female. B – C, lateral view. D, head shield. E – F, ventral margin of valve. G, posteroventral angle of valve. H – I, postabdomen. J, distal portion of postabdomen. K, postabdominal claw. L, ephippial female. M – N, juvenile male of instar II. M, outline. N, postabdomen. O – P, adult male. O, lateral view. P, postabdomen.

FIGURE 2. Camptocercus oklahomensis from USA, Louisiana, Pointe Coupe Parish, roadside ditch about 2 miles north from Highway 190 on Highway 1. A – F, parthenogenetic female. A – B, lateral view. C, dorsolateral view. D, posterior part of ventral margin of valves. E, postabdomen. F, antenna. G – I, ephippial female. G, lateral view. H, dorsal view. I, sculpture of ephippium. J – K, male. J, lateral view. K, postabdomen. Scale bars denote 0.1 mm for A – C, G – H, J, 0.05 mm for D – E, I, K, 0.01 mm for I.

FIGURE 3. Camptocercus oklahomensis from USA, Louisiana, Pointe Coupe Parish, roadside ditch about 2 miles north from Highway 190 on Highway 1. A – G, parthenogenetic female. A, head. B, head pores. C – D, labrum. E, antennule. F, antenna. G, antennule of instar II juvenile male. H – I, adult male. H, head. I, antennule and outline of rostrum.

FIGURE 4. Camptocercus oklahomensis from USA, Louisiana, Pointe Coupe Parish, roadside ditch about 2 miles north from Highway 190 on Highway 1. A – J, thoracic limbs of parthenogenetic female. A, limb I. B, IDL of limb I. C, 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 – L, thoracic limb I of instar II juvenile male. M – N, thoracic limb I of adult male.