Camptocercus lilljeborgi Schoedler, 1862

Sinev, Artem Y. & Gavrilko, Dmitriy E., 2021, Longitudinal gradient in the Camptocercus lilljeborgi Schoedler, 1862 species group (Cladocera: Anomopoda: Chydoridae), Zootaxa 5047 (2), pp. 123-138 : 124-133

Camptocercus lilljeborgi Schoedler, 1862

( Figs. 1–7 )

O.F. Müller, 1785: 77–78, Pl. 10, Figs. 1–4 ( Lynceus macrourus ); Schödler, 1862: 24 (no figures) ( C. lilljeborgi ); 1863: 36, Figs. 46–48 ( C. lilljeborgii ); Kurz, 1875: 41–43, Pl. 2: Figs. 9–10 (latirostris); Lilljeborg, 1901: 413–416, Pl. 63: Figs. 6 –13; Smirnov, 1971: 438, Figs. 534–538; Flössner, 1972: 278–280, fig. 131; 2000: 333–335, fig. 123; Negrea, 1983: 312–314, Fig. 127; Margaritora, 1985: 287–289, Fig. 113; Smirnov, 1998: 77, Figs. 58–63; Hudec, 2010: 279–281, Pl. 66: Figs. F–J; Korovchinsky et al., 2021: 306–308, Fig. 91(1–11).

Non C. lilljeborgi in Sinev, 2014: 199–204, Fig. 12–15; Garibian et al., 2019: 46, Fig. 6 .

Material studied. Russia: 1 parthenogenetic female from Volchino lake, Tver Area, N 57.76896°, E 34.90535°, 07. 2020, coll. A.A. Neplyukhina, AAK M–5881; over 50 parthenogenetic females, 2 ephippial females, 6 adult males from River Levinka , Nizhnii Novgorod, N 56.343763°, E 43.873638°, 21.09.2018, coll. D.E. Gavrilko; 5 parthenogenetic female from river Alatyr’ , Mordovia Republic, N 54.87569°, E 46.24933°, 11.08.2018, coll. E. Surkova, AAK M–5527; over 30 parthenogenetic females from a mine-lake near road Tomsk – Mel’nikovo, Tomsk Area, N 56.53575°, E 84.13392°, 20.7.2005, coll. A. A. Kotov, AAK 2005–298 .

Description. Parthenogenetic female. General. Body with a well-expressed dorsal keel, oval, moderately high ( Fig. 1A , 2A–D , 7A ); height/length ratio 0.55-0.6 in adult; maximum height at the middle of the body. Body strongly compressed laterally, with developed egg locules. Dorsal margin evenly arched from tip of rostrum to the posterodorsal angle; posterodorsal angle not defined; posterior margin convex; postero-ventral angle very broadly rounded, with a 1–4 small denticles. In lateral view ventral margin straight in anterior half, anterior angle of valves broadly rounded. In ventral view, anterior half of ventral margin forms broad aperture between the valves, with narrow rims around it. Ventral margin ( Fig. 1B ) armed with 75–85 setae, row of setae ends at half-length of margin. About 60 anterior setae ( Fig. 1C , 2E ) are densely spaced, of same length, armed with long setules distally; 15 posteriormost setae ( Fig. 1D ) are sparsely spaced, armed with short setules, decreasing in length distally. Posteroventral angle ( Fig. 1E , 2F–G , 7B ) with 1–4 short denticles with broad bases; distance between denticles about 1.5–2 widths of their bases. Valves with a distinct longitudinal, sometimes anastomosing, lines in posterior part. Keel oblique on both head and valves.

Head ( Fig. 1F , 2H , 7C ) with truncated rostrum, protruding downward. Head keel wide; distance from eye to the keel margin about 1.5–2 diameters of eye. Ocellus smaller than eye; distance from tip of rostrum to ocellus greater than distance between ocellus and eye.

Head shield with maximum width behind mandibular articulation, without distinctive sculpture. Posterior margin of head shield as prominent, acute angle with rounded tip. Three major head pores ( Fig. 3A–B ) of same size, with a narrow connection between them. PP less than 0.5 IP in adults. Lateral head pores located in small depressions about 1.5 IP distance from midline, at level of anterior major head pore.

Labrum ( Fig. 4A–B ) of moderate size. Labral keel moderately wide (height about 1.5 widths), with a blunt or rounded apex. Anterior margin of keel irregularly convex; posterior margin weakly convex, with 2 clusters of short setules.

Thorax and abdomen ( Fig. 4C ) of similar length. Dorsal surface of middle abdominal segment saddle-shaped. Abdominal joint well-developed.

Postabdomen ( Fig. 3C–D , 4D–E , 7D ) very long and narrow, unevenly narrowing distally, without defined distal margin. Length about 7–8 heights at preanal angle. Ventral margin almost straight. Basis of claws elongated, bordered from dorsal margin by a weak incision. Dorsal margin straight in postanal portion and weakly concave in anal one; distal part about 6 times longer than preanal one; postanal portion 4-5 times longer than anal one. Preanal angle well expressed, prominent; postanal angle weakly defined. Preanal margin convex. Postanal margin ( Fig. 3E , 4F–H , 7E ) with 22–24 single, quadrangular denticles with serrated outer margin, 1–2 distalmost denticles triangular; size of denticles evenly decreasing basally. Length of distal denticles slightly less than width of postabdominal claw base. Postanal portion with about 20 lateral fascicles of 4–6 short, thin setules; distalmost setule in each fascicle being longest. Postabdominal claw ( Fig. 3F , 4I , 7F ) almost straight, very long, of about twice the length of preanal portion of postabdomen; with distinctive pectens of setules on dorsal margin. Distalmost element in basal pecten is a spine, with a length less or equal to claw width at the spot. Basal spine slender, weakly curved, about 1/5 length of the claw, with short spinules on dorsal margin.

Antennule ( Fig. 4J ) long, with strongly curved basal portion, not reaching the end of the rostrum; length about 5 widths; with a cluster of setules on outer margin. Antennular seta of moderate length, about half length of antennule itself, arising at 2/3 distance from the base on a weakly-defined tubercule. Nine terminal aesthetascs, the longest slightly shorter than antennules, others much shorter about 1/3–2/3 length of antennule.

Antenna relatively short ( Fig. 2I , 4K ). Antennal formula: setae 0–0–3/0–1–3; spines 1–0–1/0–0–1. Basipodite robust, with very short seta between branches. Branches long and slender; in both branches apical and middle segments of same length; basal segment 1.5 times longer and thicker than two others. Seta arising from middle segment of endopodite short, shorter than endopodite.All apical setae of similar thickness. Spine on basal segment of exopodite about 1/3 the length of middle segment. Spine on apical segment of exopodite about 1/2 length of the segment. Spine on apical segment of endopodite about 1/3 length of the segment.

Limb I ( Fig. 6A–C , 7G ). Epipodite oval, with very long, thick, strongly curved projection. Accessory seta long, about 1/2 length of ODL seta, armed with long setules distally. ODL seta with short setules in distal part. IDL with three setae; seta 1 thick, curved, only slightly shorter than seta 2, with short spinules in distal portion. IDL setae 2 and 3 of moderate thickness, not hook-like, armed with robust setules in distal part; seta 3 about 3/4 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 seta d similar in size and morphology to setae a–b, setae e–f of moderate thickness, with long setules in distal portion, and a naked inner seta (2) and small sensillum on anterior face of limb. Seta e about 3/4 length of limb itself, seta f slightly shorter than seta e. Endite 1 with two long 2-segmented setae of similar size (g–h), setulated in distal part, short flat curved seta i, and a naked inner seta (3), 1.5 times longer than inner seta of endite 2; on anterior face of limb, very small sensillum located near the base of seta 3.

Limb II ( Fig. 6D–F ). Exopodite elongated, of irregular shape, with short seta. Eight scraping spines: scrapers 1–2 and 4–5 long; scraper 3 shorter than neighbors, armed with thick denticles; scrapers 6–8 subequal in length; scraper 6 two times shorter than scraper 5. Scrapers 3–4 armed with robust denticles. 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. 6G–H ). Epipodite with projection as long as exopodite itself. Exopodite of irregular shape; setae 1–2 short, thin plumose; seta 3 being the longest, with very thick basal portion, in distal portion armed with dense setules; seta 4 very short, with broad semicircular base and narrow distal portion; seta 5 very small, triangular; seta 6 and 7 thin, bilaterally armed with short thick setules in distal portion, seta 6 slightly shorter than seta 3, seta 7 about 1/2 length of seta 3. Distal endite with three setae; small sensillum located between bases of setae 1 and 2. Two distalmost setae (1–2) slender, sharp, with thin setules in distal part, seta 2 much thinner and 1.5 times shorter than seta 1; basalmost seta (3) as long as seta 1, flattened and setulated in distal portion. Basal endite with 4 stiff setae (a–d), thick, setulated in distal part, increasing in size basally. 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. 6I–K , 7H ). Pre-epipodite setulated; epipodite oval, with projection 1.5 times longer than epipodite itself. Exopodite of irregular shape, with six setae; seta 3 being longest. Setae 1–2 of about 2/3 length of seta 3, plumose; seta 3 with very thick basal portion and densely setulated distal portion; seta 4 very short, with broad semicircular base and narrow distal portion; seta 5 slightly shorter than seta 3, with densely setulated distal portion; seta 6 of about 1/3 length of seta 3, narrow, curved, without setules. Inner portion of limb IV with four setae, a large rounded sensillum arising from the side of lobe. Scraping seta (1) short, broad; three flaming-torch setae (2–4) with broad bases, armed with short 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. 6L–M ). Pre-epipodite setulated; epipodite oval, with projection 1.5–2 times longer than epipodite itself. Exopodite large, rounded, with four setae, seta 3 being longer. Setae 1–2 plumose, about 2/3 length of seta 3; seta 3 plumose, with very thick basal portion; seta 4 very short, triangular with rounded tip. Inner lobe small, narrow, with cluster of setules in distal portion. At inner face, two setae, one slightly longer and thicker than other, densely setulated in distal part; large rounded sensillum located near the base of smaller seta. Filter plate V of single short seta.

Ephippial female. Body slightly higher than in parthenogenetic female ( Fig. 1G , 5A ). Ephippium ( Fig. 5B ) light brown in preserved specimens, with defined egg locules covered by longitudinal lines thicker than on the rest of the valve.

Male. General. Body low oval in both juvenile males of instar II ( Fig. 1H ) and adult ( Fig.1I , 5 C-D), with well developed dorsal keel on head and valves; height/length ratio 0.55 in adult; maximum height before midline. Body strongly compressed laterally. Setae on ventral margin of valves ( Fig. 1J ) same as in female.

Head ( Fig. 1K ) with truncated rostrum. Ocellus and eye of same size as in female, distance between tip of rostrum and ocellus equal to that between ocellus and eye.

Postabdomen. In instar II juvenile male ( Fig. 4L ) similar in shape and armament to that of female; sperm ducts opening located at ventral margin of postabdomen, at 1/6 postabdomen length from the base of claws. In adult ( Fig. 4N–P , 5E–F ) very long and narrow, with almost parallel margins in postanal portion, without defined distal margin and dorso-distal angle. Length about 6.5 heights at preanal angle. Sperm ducts openings located at the ventral margin of postabdomen at 1/7 postabdomen length from the base of claws. Dorsal margin almost straight in postanal portion and weakly concave in anal one, with postanal portion 3.5 times longer than anal one. Preanal angle welldefined, postanal angle weakly defined. Preanal margin convex. Postanal margin armed with 22–25 short broad comb-like composite denticles, with low base, bearing 4–7 spinules; central spinules being longer. Lateral fascicles of setules as in female. Postabdominal claw straight with weakly curved distal portion, shorter than in female, with basal pecten consisting of a single thick spine, slightly longer than width of the claw at the spot, and about 20 thin setules. Basal spine short, curved, its length only slightly greater that width of claw base.

Antennule. In instar II juvenile male ( Fig. 4M ) similar to that of female, with short anlage of male seta. In adult male ( Fig. 4Q ) shorter than in female, strongly curved in basal half, not reaching before the end of rostrum; length about 3.5 widths. Male seta thin, about 1/3 length of antennule. arising at 1/4 distance from the base. Twelve terminal aesthetascs of about 1/2 – 2/3 length of antennule.

Limb I. In instar II male ( Fig. 6N–O ), copulatory hook curved. Ventral face of limb with anlage of copulatory brush seta and a row of about 15 short setules below it. IDL with anlage of male seta; setae 1–3 similar to those of female, but shorter. In adult male ( Fig. 6P–R ) with U-shaped copulatory hook, 2.5 times shorter than limb itself. IDL seta 1 strongly shorter and thinner than in female, about 1/4 length of seta 3; setae 2 and 3 shorter and thinner than in female, armed with dense thin setules; male seta almost straight, of moderate thickness, slightly shorter than IDL seta 3. Ventral face of limb below copulatory brush with double row of densely spaced thick setules, the ones at the middle of row being longest. Copulatory brush seta short, about half length of IDL seta 3. Seta 1 of endite 3 thinner than in female, other setae of endites 1–3, including characteristic curved seta e, same as in female.

Size. In single studied instar I juvenile female, length was 0.59 mm, height 0.33 mm; in instar II juvenile female, length 0.68– 0.7 mm, height 0.38–0.39 mm; in adult parthenogenetic female, length 0.74–1.01 mm, height 0.41–0.6 mm. In instar II juvenile male, length 0.63–0.65 mm, height 0.35–0.37 mm; in adult male, length 0.65–0.71 mm, height 0.37–0.4 mm.

Differential diagnosis. C. lilljeborgi clearly differs from most species of the genus in densely located anterior setae on the ventral margin of the valves. This character is shared only by its sibling-species, C. smirnovi sp. nov. from which differs by having a higher body, setae of ventral margin ending at half-length of ventral margin, longer and narrower postabdomen, and longer IDL seta 1 of thoracic limb I. Other differences between these two species are summarized in Table 1.

Distribution. North and Central Europe, Western Siberia.

Ecology. Flössner (1972) and then Błędzki & Rybak (2016) characterise the species as rare and not abundant, acidophilic, thermophilic, associated with vegetation ( Potamogeton, Polygonum, Stratiotes, Salvinia ), and inhabiting shallow and small water bodies such as the littoral of lakes, rivers, river floodplains, lagoons and small reservoirs. In the Levinka River, C. lilljeborgi was found at an average depth about 0.6 m, Secchi disc water transparency 0.25 m, рН 7.49, conductivity 393 µS/cm, in stands of Potamogeton natans with some Utricularia vulgaris . Specimens of C. lilljeborgi are able to slug-like attachment to flat substrate, similar to that described by Fryer (1968) for the species of genus Graptoleberis Sars, 1862 . Attached specimens move forward rather slow, passing distance of 1-2 body length in minute.

0.55–0.6 in adult female

Ventral margin of valves Convex; row of setae ends at half-length of Almost straight; row of setae ends at two-third the valve length of the valve.

Postabdomen Length about 7–8 heights at preanal angle, Length of about 6–6.5 heights at preanal angle, with with 22–24 postanal marginal denticles 16–21 marginal denticles

Marginal denticles of Except distalmost one–two, quadrangular Triangular with serrated posterior margin postabdomen with serrated outer margin

Ventral margin of Only single distal element in basal pecten is Several distal elements in basal pecten are spines, postabdominal claw spine, its length less or equal to claw width length of distalmost spine exceed claw width at the at the spot spot

IDL seta 1 Long, 1.5 times shorter than seta 3 Short, three times shorter than seta 3

Limb II Scrapers 3 and 4 bear spinules of equal size Scraper 3 bear much thicker spinules that scraper 4

Exopodite IV Seta 5 shorter than seta 3; Seta 5 longer than seta 3;

setae 1–2 long, 1.5 times shorter than seta 3 setae 1–2 very short, 5 times shorter than seta 3

Length of adult female 0.74–1.01 mm 0.65–0.82 mm

Figures

FIGURE 1. Camptocercus lilljeborgi Schoedler, 1862 from River Levinka, Nizhnii Novgorod, Russia. Parthenohenetic female: A, lateral view; B, ventral margin of valves; C, setae of anterior group of ventral margin of valves, setulae shown only on posterior setae; D, posterior group of setae of ventral margin of valves; E, posteroventral angle of valves; F, head. Ephippial female: G, lateral view. Juvenile male of instar II: H, lateral view. Adult male: I, lateral view; J, ventral margin of valves; K, head.

FIGURE 2. Camptocercus lilljeborgi Schoedler, 1862 from River Levinka, Nizhnii Novgorod, Russia. Parthenogenetic female. A–B, lateral view. C, dorsal view. D, ventral view. E, setae of anterior group of ventral margin of valves. F–G, posteroventral angle of valves. H, head. I, antenna.

FIGURE 3. Camptocercus lilljeborgi Schoedler, 1862 from River Levinka, Nizhnii Novgorod, Russia. Parthenogenetic female. A, head pores. B, major head pores. C–D, postabdomen. E, distal portion of postabdomen. F, postabdominal claw.

FIGURE 4. Camptocercus lilljeborgi Schoedler, 1862 from River Levinka, Nizhnii Novgorod, Russia. Parthenogenetic female: A–B, labrum; C, abdominal joint; D–E, postabdomen; F–G, distal portion of postanal margin of postabdomen; H, anal margin of postabdomen; I, postabdominal claw; J, antennule; K, antenna. Juvenile male of instar II: L, postabdomen; M, antennule.Adult male: N, postabdomen; O, distal portion of postanal margin of postabdomen; P, postabdominal claw; Q, antennule.

FIGURE 5. Camptocercus lilljeborgi Schoedler, 1862 from River Levinka, Nizhnii Novgorod, Russia. Ephippial female: A, lateral view; B, sculpture of ephippium. Adult male: C–D, lateral view; E–F, postabdomen.

FIGURE 6. Camptocercus lilljeborgi Schoedler, 1862 from River Levinka, Nizhnii Novgorod, Russia. Parthenogenetic female, thoracic limbs: A, limb I; B, setae a–b of limb I; C, IDL and ODL of limb I (setules on ODL seta did not shown); D, exopodite of limb II; E–F, inner and outer portions of limb II; G, exopodite of limb III; H, distal endite of limb III; I, exopodite of limb IV; J–K, inner portion of limb IV; L, limb V; M, inner setae of limb V. Juvenile male of instar II: N–O, anterior margin and IDL of limb I. Adult male: P, thoracic limb I; Q–R, ODL and IDL of limb I.

FIGURE 7. Camptocercus lilljeborgi Schoedler, 1862 from mine-lake near road Tomsk–Mel’nikovo, TomskArea, Russia. Parthenogenetic female. A, lateral view. B, posteroventral margin of valves. C, head. D, postabdomen. E, distal portion of postanal margin of postabdomen. F, postabdominal claw. G, IDL and ODL of thoracic limb I. H, exopodite of thoracic limb IV.