Eurycercus pompholygodes Frey, 1975

Bekker, Eugeniya I., Kotov, Alexey A. & Taylor, Derek J., 2012, A revision of the subgenus Eurycercus (Eurycercus) Baird, 1843 emend. nov. (Cladocera: Eurycercidae) in the Holarctic with the description of a new species from Alaska, Zootaxa 3206 (1), pp. 1-40 : 16-19

Eurycercus pompholygodes Frey, 1975

Fig. 5

Eurycercus pompholygodes Frey, 1975, p. 270 –284, Figs 1 –31; Kotov et al. 2010b, p. 234 –235, Fig. 137(12–14).

Type locality. “Bythotrephes Pond, located about 1 km northwest of the limnological station at Kuokkel and about 5 km north of Björkstugan at the west end of Tome Träsk in Swedish Lapland" ( Frey 1975). Approximate geographic coordinates: 68.4, 18.4

Type material. Holotype. A parthenogenetic female 1.92 mm long in alcohol, NHM 1973.845 .

Paratypes. Two parthenogenetic females in alcohol, one parthenogenetic female on a slide in glycerine jelly, and three exuviae mounted individually in polyvinyl lactophenol on the same slide, NHM 1973.846 - 849 . One parthenogenetic female in alcohol, one parthenogenetic female on a slide in glycerine jelly, and three exuviae mounted individually in polyvinyl lactophenol on the same slide, USNM 143768 . One parthenogenetic female and three exuviae in polyvinyl lactophenol on the same slide ( ZIN, accession numbers 2656 and 2667), one parthenogenetic female and three exuviae in polyvinyl lactophenol on the same slide, ZIN ( ZIN, accession numbers 2658 and 2659). Some other specimens were kept in the D. G. FREY collection in Bloomington, now they are in USNM (accession number of whole DGF is USNM 403774 ) .

Material examined here: Sweden. Small pond ca. 8 m within 100 m of Abisko Turiststation, coll. in. 20.07.1972 by D. G. Frey, DGF 3260 (68.358, 18.783); Bythotrephes pond, north of Kuokkel, Abisko, coll. in 27.07.1972 by D. G. Frey, DGF 3268 (68.4, 18.4)

Russia. Komi Autonomous Republic. A bay of the Kozhim-Yu River, Pechora-Ilych National Reserve , coll. in 20.07.2010 by A. A. Kalinin, AAK M-1619 (63.1514, 59.0225); Kurja near Scheljajur, coll. in 10.08.1982, AAK 1999-043 (65.33, 53.4) . Murmansk Area. A small lake near the Belomorskaya Biological Station of Moscow State University, coll. in 08. 1995 by A. Yu. Sinev, AAK 2004-020 (66.5, 33.1); Lake Bolshoy Vudjavr, coll. in 01.08.2009, AAK M-1404 (67.6306, 33.673). Taimyr Autonomous Area. A tarn at Talnah, coll. in 11.08.1974 by Y. I. Chernov, AAK 1999-075 and AAK 1999-049 (69.5, 88.4); Lake №6, River Tareya , a tributary of River Pyasina , coll. in 11.08.1974 by Y. I. Chernov, AAK 1999-074 (73.3, 90.8) .

Diagnosis. Parthenogenetic female. Dorsal head pores on a bubble-like projection located immediately on head shield. In anterior view, body wide, not compressed laterally, median dorsal keel absent. Rostrum relatively long. Ocellus minute. Lateral head pore elongated. Labrum with a relatively small median keel, broadly rounded, reaching only half of antenna I length. Postabdomen with sub-parallel dorsal and ventral margins, preanal teeth pointed. Spines at base of pre-claw portion predominantly clustered. Antenna I with antennular sensory seta arising in middle. Denticles in rows encircling antennular surface especially small. On antenna II, spine situated on proximal segment of exopod somewhat shorter than second segment. Limb I IDL with a remarkably strong hook-like seta, the smallest IDL seta especially fine and short. IDL with 6–4 distal spinules, 6–10 proximal spinules, 3–6 marginal spinules and 1–2 basal spinules. Eight setae in filter plate II, 8 setae in filter plate III; 9 setae in filter plate IV, 8 setae in filter plate V.

Full description of parthenogenetic female, ephippial female, male. See Frey (1975).

Short redescription. Parthenogenetic female. In lateral view ( Fig. 5A ) body in larger females ovoid (BH/ BL=0.60–0.66), but in juveniles more sub-rectangular, than in other species. Dorsal margin interrupted by a dorsal bubble bearing head pores. In anterior of ventral view, body wide, not compressed laterally, median dorsal keel is absent ( Fig. 5B–C ). Intestine has a single loop, posterior intestinal caecum present. Few eggs in the brood pouch.

Head with short rostrum ( Fig. 5D ). A single major “head pore” as a ringed, sub-oval field of special cuticle; a minute, elongated lateral pore located at either side of major pore, closer to it ( Fig. 5E ).

Labrum with a small, rounded median keel, reaching only about middle of antenna I ( Fig. 5A, D ).

Armature of valve margin as in previous species (VL/BL = 0.81–0.86), with sub-parallel dorsal and ventral margins ( Fig. 5F ).

Postabdomen. Distal anal embayment shallow. Armature of the preanal margin as a series of preanal teeth (NT about 83), distalmost tooth remarkably larger than others; small gap lacking any teeth at base of postabdominal setae; teeth in middle of preanal margin with sharp tips. Distalmost postanal teeth on pre-claw portion long, thin, predominantly double, teeth on pre-claw portion shorter, generally clustered (doubled or tripled) ( Fig. 5G , arrows). Postabdominal claw robust (CL/PL = 0.26–0.30); first (distalmost) basal spine long (DS/CL = 0.36–0.50), second (basalmost) spine short (BS/CL = 0.18–0.25; BS/DS about 0.5).

Antenna I ( Fig. 5H ) short relatively body length (AL/BL = 0.11–0.13), but protruding greatly beyond labral keel and tip of rostrum; elongated (AL/DA = 2.3–3.3), triangular in cross section. Antennular sensory seta arising near the middle of the antenna I. Denticles in rows encircling antennular surface especially small, ridges on the body of antenna I absent.

Antenna II. Spine situated on proximal segment of exopod somewhat shorter than length of second segment.

Limb I with IDL supplied with three bisegmented setae generally decreasing in size towards endites, among them, a strong hook-like seta, but not too large like one in E. macracanthus . IDL supplied with 4–6 long distal spinules, 6–10 long proximal spinules, 3–6 short marginal spinules and 1–2 very short basal spinules. Other limbs as in previous species, filter plate III with 9–10 setae, IV and V limbs with 8 setae.

Size. 0.69–01.67 in our material, 0.62–2.36 according to Frey (1975).

Comments. It is a well-defined Arctic-Subarctic taxon with a characteristic short labral keel.

Distribution. This taxon was known only from Swedish Lapland ( Frey 1975) and a few localities in Norway ( Hessen & Walseng 2008). Now it is clear that E. pompholygodes occurs in the north of European Russia and even on the Taimyr Peninsula. The range could reach the eastern part of the Siberian Subarctic.

Ecology. Frey (1975, p. 265–266) wrote that the species is present in the waters bodies where "water has a low concentration of electrolytes, tends to be acidic, and quite frequently has a perceptible humic color", and that it sometimes co-occurs with E. lamellatus . We found that E. pompholygodes is present in subarctic water bodies of different types: tundra ponds of different size, small or large lakes, and bays of rivers.

Figures

FIGURE 1. Distribution of species from the subgenus Eurycercus (Eurycercus) emend. nov. in the Holarctic according to our original samples—no literature data included. E. lamellatus—grey circles. E. macracanthus—black circles. E. pompholygodes—solid quadrates (red in electronic version). E. microdontus—black stars. E. longirostris—grey quadrates. E. nipponica—solid triangles (green in electronic version). E. beringi sp. nov.—black crosses.

FIGURE 5. Eurycercus pompholygodes, parthenogenetic female from Lake №6 near River Tareya, a tributary of River Pyasina, Taimyr Autonomous Area, Russia. A, lateral view. B, ventral view. C, anterior view. D, head. E, head pores. F, postabdomen. G, its distal portion. H, antenna I. I–J, inner distal lobe of limb I. Scale bar denotes 1 mm (A–C); 0.1 mm (D–J).