Ceriodaphnia quadrangula (O.F. Müller, 1785)

(Figs. 1–3)

Daphnia quadrangula O.F. Müller, 1785: 90, pl. 13, figs. 3–4.

Ceriodaphnia quadrangula var. quadrangula .— Lilljeborg 1901: 193–196, tab. XXVII, fig. 16–25.

Ceriodaphnia quadrangula .— Šrámek-Hušek et al. 1962: 234–236, obr. 83a–i.

Ceriodaphnia quadrangula .— Flössner 2000: 205–207, abb. 77a–i.

Ceriodaphnia quadrangula .— Hudec 2010: 147–150, tab. 29a–l.

Ceriodaphnia quadrangula .—Kotov et al. 2010: 187, figs. 5–6.

Ceriodaphnia quadrangula .— Kotov et al. 2018: 113–115, figs. 7a–h, 8a–f.

? Ceriodaphnia quadrangula .— Matile 1890: 22, fig. 15.

? Ceriodaphnia quadrangula var. hamata .— Lilljeborg 1901: 196–198, tab. XXVIII, fig. 1–5.

? Monospilus clathratus .— Jurine 1820: 140–141, figs. 5–6 (see synonymy for C. quadrangula in Flössner 2000).

Type locality. Precise type locality is unknown, but the most part of O.F. Müller’s material was collected from the ponds near Copenhagen “ Frederiksdal, located slightly north-west of Copenhagen between Fuersø and Bagsvaeds Sø ” (Frey 1980) .

Type material. Lost, as whole material of O.F. Müller (Frey 1980).

Material examined. Several parthenogenetic females, ephippial females and males from Lake Gribsø (55.984606°N, 12.303347°E), Denmark, coll. D.B. Berner, August 1993. This material was preserved in sucroseformalin and in dilute formalin+glycerine .

Other material examined. Five parthenogenetic females, 10 ephippial females, 2 males from Lake Dubrovskoje (58.56°N, 37.62°E), Darvin Reserve, Vologda Area, coll. V. I. Lazareva in September of 1995, AAK 2004-023; 5 parthenogenetic females, 5 ephippial females, 1 male from Kavgolovskoe Lake (60.1752°N, 30.5270°E), Leningrad Area, coll. A. V. Makrushin in 18.09.1985, NNS 2000-075 .

Redescription. Parthenogenetic female (Figs. 1–2). General (Fig. 1A). Body rounded in lateral view, typical for genus (body height/length=0.68), maximum height in middle portion. Dorsum of valves broadly convex, with prominent dorsolateral depression between head and rest of body (Fig. 1A). Posterodorsal angle well visible. Ventral margin broadly rounded, smoothly passing to anteroventral margin. No integumental setae on head and valves (Fig. 1A). Body laterally compressed, elongated and subovoid in dorsal and ventral view.

Head (Figs. 1B–C) small, with short rostrum and voluminous supraocular dome surrounding large compound eye (Fig. 1B). Posterior margin of dome forming depression. Minute ocellus slightly elongated, located near base of antenna I (Fig. 1B). Frontal head pore not revealed (Fig. 1C). Dorsal head pore absent (Fig. 1B).

Labrum (Fig. 1B) with wide, fleshy main body and large, setulated distal labral plate.

Valves (Figs. 1A, D) large, almost rounded. From inner side, anteroventral and ventral margins with row of setae, covered by fine setulae (Fig. 1D), posteriorly this row represented by only fine setulae (Fig. 1E), although two or three short setae located in last one-third of ventral margin (Fig. 1D). Caudal spine and lateral protuberances absent (Figs. 1A, D).

Thorax relatively long, abdomen short, with single abdominal projection.

Postabdomen (Fig. 1F) elongated, subrectangular. Ventral margin almost straight or slightly concave. Large anus located among base of postabdominal claws. Preanal margin long and slightly concave or straight (Fig. 1F). Anal margin three times shorter than preanal margin. Preanal and anal margins with seven to nine pairs of sharp denticles twice longer than thickness of base of postabdominal claw, and provided with group of small setulae at base. Laterally, curved rows of small denticles located above row of spines on anal portion (Fig. 1F). Small additional bunches of setulae located on dorsal and lateral sides of preanal portion.

Postabdominal seta (Fig. 1A) as long as postabdomen; its distal and proximal segments subequal in length. Distal segment covered by short fine setulae.

Postabdominal claw (Fig. 1F) massive, evenly curved, with particularly sharp, pointed tip. On outer side of claw with two successive pectens along dorsal margin, proximal one consisting of thin small denticles, distal one also of thin small denticles decreasing in length distally, with proximal ones larger than those of proximal pecten.

Antenna I (Fig. 1G) cylindrical, thin, short (length about 3 diameters), without prominent rows of setulae. Antennular sensory seta slender, twice longer than antennula body, arising subdistally from inflated protuberance (Fig. 1G). Nine short aesthetascs subequal in size (Fig. 1G).

Antenna II long (Fig. 1H). Coxal part with two equal sensory setae. Basal segment robust, covered by transverse rows of hairs, with distal sensory seta on anterior face. Antennal branches elongated with all segments cylindrical, covered by rows of short hairs; first endopod segment almost as long as first two exopod segments. Antennal formula: setae 0-0-1-3/1-1-3; spines 0-0-0-0/0-0-0. Both exopod and endopod branches with three long, apical swimming setae, all with basal and distal segments bilaterally feathered by fine, long setulae. Lateral setae of exopod and endopod with same armature. Apical spines absent.

Thoracic limbs: five pairs (Figs. 2A–G).

Limb I (Fig. 2A) with elongated corm; outer distal lobe with long seta unilaterally armed distally with short setulae and short thin seta. Inner distal lobe (or endite 5 sensu Kotov 2013), with three unequal setae (Fig. 2A) armed with short stiff setulae. Endite 4 with single anterior seta (Fig. 2A: 1) and two posterior setae (Fig. 2A: a–b). Endite 3 with single anterior seta (Fig. 2A: 2) and two posterior setae (Fig. 2A: c–d). Endite 2 with single short anterior seta (Fig. 2A: 3) and four posterior setae (Fig. 2A: e–h). Two ejector hooks of similar size. No maxillar process on limb base (Fig. 2A).

Limb II (Figs. 2B–C) large. Limb distal portion (exopodite) as large elongated lobe with two soft unequal setae. Endite 5 with single very small stiff anterior seta and two soft posterior setae (Figs. 2B–C: a–b). Endite 4 with single stiff anterior seta four times longer than single anterior seta of endite 5, and single posterior soft seta (Figs. 2B–C: c). Endite 3 with single anterior stiff seta two times shorter than single anterior stiff seta of endite 4. Endite 2 with single anterior stiff seta (represented by small sensillum), single posterior soft seta (Figs. 2B–C: d) and small seta of unknown homology. Gnathobase (or endite 1) with two clear rows of setae. Anterior row includes small sensillum (Figs. 2B–C: 1), long seta armed unilaterally by long setulae (Figs. 2B–C: 2), shorter seta (Figs. 2B–C: 3) also armed unilaterally by short setulae and very short and thin seta (Figs. 2B–C: 4) in central part of “filter plate”. Posterior row consists of eight setae (Figs. 2B–C: a–h).

Limb III (Figs. 2D–E) with ovoid epipodite. Exopodite flat, bearing two lateral setae (Fig. 2D: 5–6) and four distal setae (Fig. 2D: 1–4). Distal segment of seta1 very thin (Fig. 2D: 1). Innerdistal portion with five endites (Figs. 2D–E). Endite 5 with two setae (Fig. 2E: a–b). Endite 4 with two setae (Fig. 2E: c–d). Endite 3 with single seta (Fig. 2E: e). Endite 2 with two long setae (Fig. 2E: f–g). Remainder of limb inner portion (endite 1) with single large lobe, bearing single anterior seta (Fig. 2E: 1), two short stiff anterior setae and numerous posterior setae (Figs. 2D–E).

Limb IV (Fig. 2F) with subovoid epipodite. Exopodite flat, broadly rounded with two lateral soft setae (Fig. 2F: 5–6) and four distal soft setae (Fig. 2F: 1–4). Inner distal portion of limb not subdivided into endites, distally with two short setae of unclear homology (Fig. 2F: 1–2). Most of limb inner margin a gnathobase filter plate consisting of numerous posterior long setae (Fig. 2F).

Limb V (Fig. 2G) with setulated preepipodite and large subovoid epipodite. Exopodite ovoid, with long distal seta, two short medial setae, and an especially large lateral seta (Fig. 2G). Inner limb portion an ovoid flat lobe, with setulated inner margin and single, large seta (Fig. 2G).

Ephippial female (Fig. 3A). General body shape and appendages of ephippial female appearing similar to those of parthenogenetic female (Fig. A). Dorsal portion of body in ephippial female transformed into ephippium, clearly bordered from rest of body. In lateral view, ephippium narrowing posteriorly. Dorsal margin slightly convex to almost straight; ventral margin regularly curved from posteroventral to anteroventral angle. Depression along dorsum separating two halves of ephippium well-visible. Sculpture of dorsal portion of ephippium represented by relatively thick small columns with branched tips (Kotov et al. 2018: figs.7a, d 8c, e). Egg locule visibly extending laterally (Kotov et al. 2018: figs. 7b, c). Ornamentation of egg locule represented by small columns with branched tips in lateral side and on central portion (Kotov et al. 2018: figs. 7e–g). Posteroventral, ventral and anterior portions of ephippium covered by small tubercles with short processes (Kotov et al. 2018: fig. 7g). Ephippium containing single resting egg.

Male (Figs. 3B–H). General (Fig 3B). In lateral view body ovoid, more elongated compared to female (body height/length about 0.54). Dorsal margin of valves not elevated above head, posteroventral angle distinct.

Head (Figs. 3B–D) small and relatively longer than in female. Dorsal head pore absent. Compound eye large (Fig. 3B). Ocellus slightly elongated, located near base of antenna I (Fig. 3B).

Valves (Fig. 3B) ovoid, more elongated than that in female. Armature of inner side as in female.

Postabdomen (Fig 3E) generally as in female. Gonopores (Fig 3E: gp) open laterally at beginning of distal onethird of postabdomen. Anal denticles as in female, but less numerous.

Antenna I (Fig 3F) long, straight, covered by prominent small stiff setae. Antennular sensory seta long, arising subdistally from antennular body. Male seta especially robust, located in distal portion of antennular body and three times longer than this. Nine terminal aesthetascs on opposite side to antennular sensory seta.

Limb I (Fig. 3G) with large, curved copulatory hook. ODL (exopodite) with two setae, one being especially long, bi-segmented, distal portion covered by fine short denticles. IDL (endite 5) additionally with short seta of unknown homology. Additional seta also located near anterior seta 1.

Limb II (Fig. 3H) with distal portion (exopodite) similar to female. Endite 5 with single small anterior stiff seta and two posterior soft setae (Fig. 3H: a–b). Endite 4 with single anterior stiff long seta unilaterally armed distally with short setulae, and single posterior soft seta (Fig. 3H: c). Endite 3 with single soft seta. Endite 2 with single anterior stiff seta (represented by small sensillum), single posterior soft seta (Fig. 3H: d) and small seta of unknown homology. Gnathobase (or endite 1) similar to parthenogenetic female. Sexual dimorphism in structure of limb II in C. quadrangula present: anterior seta near posterior seta c in female represented by small stiff seta, as relatively long in male; endite 3 with short stiff seta in female, with relatively long, soft seta in male. Sexual dimorphism in structure of limb II previously found in some species of Daphnia and Simocephalus (see Kotov 2013).

Size. Adult parthenogenetic females up to 1.2 mm in length; ephippial females up to 0.60 mm in length; adult males up to 0.53 mm in length.

Variability. No significant variability was found in studied individuals from Denmark.

Distribution and ecology. Ceriodaphnia quadrangula sensu lato has been cited from all biogeographical regions: Palaearctic, Nearctic, Neotropical, Afrotropical, Oriental and Australasian zones (Kotov et al. 2013). However, in the frame of the non-cosmopolitanism concept in the cladoceran distributions, it is most likely, that the distribution of C. quadrangula sensu stricto is restricted to the western Palaearctic (mainly Northern and Central Europe and European part of Russia).

Ceriodaphnia quadrangula is mainly planktonic and characteristic of large and medium-sized lakes with low mineralized and oligo-mesotrophic waters.