Eurycercus nipponica Tanaka & Fujita, 2002

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 : 24-26

Eurycercus nipponica Tanaka & Fujita, 2002

Figs 8–9

Eurycercus nipponica Tanaka & Fujita, 2002, p. 13 , Pl. 5: figs 1–2, Pl. 6: figs 1–2, Pl. 7: figs 1–6; Tanaka et al. 2004, p. 172.

Type locality. "Lake Utonai-numa" ( Tanaka & Fujita 2002) =Unonaito-numa, Hokkaido, Japan. Approximate geographic coordinates: 42.70, 141.71.

Holotype. A female with number Y7860825, but the place if its deposition unclear, and absent in the first description ( Tanaka & Fujita 2002).

Material examined here: Japan. Nagano. Aoki Ko, coll. in 06.12.2006 by S. Tanaka, DJT 4-235, DJT 4-236 (36.6089, 137.8542) ; Kizaki Ko, coll. in 06.12.2006 by S. Tanaka, DJT 4-237 (36.5557, 137.8408).

Russia. Kamchatka Area. A bay of Kurilskoe Lake, coll. in 08.2009 by A. A. Kotov, AAK 2009-104 (51.41754, 157.0459) ; A swampy area near Travianoy Cape , Kurilskoe Lake, coll. in 08.2009 by A. A. Kotov, AAK 2009-103 (51.4172, 157.0454) ; A swampy area (with a fresh bear trail in time of sampling) near Travianoy Cape , Kurilskoe Lake, coll. in 16.08.2009 by A. A. Kotov, AAK M-1352 (51.4165, 157.0450) ; Tundra lake 1 near Kurilskoe Lake , coll. in 16.08.2009 by A. A. Kotov, AAK M-1353 (51.4101, 157.0490) ; Tundra lake 4 near Kurilskoe Lake , coll. in 16.08.2009 by A. A. Kotov, AAK M-1357 (51.4090, 157.0517) ; A forest puddle 1 near the Plotnikova River, coll. in 13.08.2009 by A. A. Kotov, AAK M-1344 (52.9208, 157.1527); A forest puddle 2 near the Bystraya River, coll. in 08.2009 by A. A. Kotov, AAK 2009-093 (52.9264, 156.6012) ; An affluent of the Bystraya River, coll. in 08.2009 by A. A. Kotov, AAK 2009-094 and AAK M-1376 (52.9304, 156.6031) ; Bolshaya River near the KamchatNIRO station, coll. in 13.08.2009 by T. N. Travina, AAK 2009-079 (52.7612, 156.2647) ; Small lake near Lake Azabachje on Cape Ivashka , coll. in 02.10.1985, NNS 1999-008 , NNS 1999-017 and AAK 1999- 077 (56.16, 161.85) .

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 small. Lateral head pore minute, circular. Labrum with a large median keel, terminating in an angled apex, reaching distal end of antenna I. Postabdomen with sub-parallel dorsal and ventral margins, preanal teeth pointed. Spines at base of pre-claw portion predominantly single. Antenna I with antennular sensory seta arising somewhat basally to middle. Denticles in rows encircling antennular surface relatively large. On antenna II, spine situated on proximal segment of exopod equal to or somewhat shorter than second segment. Limb I IDL with a strong hook-like seta, the smallest IDL seta especially short. IDL with about 11 distal spinules, about 8 proximal spinules, about 6 marginal spinules and about 10 basal spinules. Eight setae in filter plate II, 8 setae in filter plate III; 8 setae in filter plate IV, 8 setae in filter plate V.

Short redescription. Parthenogenetic female. In lateral view body sub-ovoid in larger females ( Fig. 8A ), maximum height of the body in its middle portion (BH/BL= 0.50–0.66). Dorsal margin interrupted only by a bubble-like head pore. In anterior or ventral view, body wide, not compressed laterally ( Fig. 8D ), maximum width of body at level of mandibular articulation, median dorsal keel absent. Intestine has a single loop, posterior intestinal caecum present. Few eggs in the brood pouch.

Head with short rostrum ( Fig. 8E ). A single major “head pore” as a ringed, sub-oval field of special cuticle located on a dorsal bubble. A minute, circular lateral pore located at either side of major pore, closer to it ( Fig. 8F ).

Labrum fleshy body with paired lateral horn-like projections, a large median keel terminating in an angled apex ( Fig. 8E ).

Valves generally ovoid (VL/BL= 0.84–0.96), as in previous species.

Postabdomen large (PL/BL= 0.27–0.43), relatively broad ( PH /PL= 0.45–0.46), with sub-parallel dorsal and ventral margins ( Fig. 8G ). Distal anal embayment very shallow. Armature of the preanal margin as a series of preanal teeth (NT=101); small gap lacking any teeth at base of postabdominal setae ( Fig. 8I ); teeth in middle of preanal margin with sharp tips, distalmost tooth equal to or somewhat larger than others. Distalmost postanal teeth particularly large, predominantly clustered, teeth at base of pre-claw portion (=at distal part of anal margin) predominantly single ( Fig. 8H , arrows). Postabdominal claw relatively robust (CL/PL= 0.16–0.24); basal spines, first (distal) long (DS/CL= 0.25–0.38), second (basal) short (BS/CL= 0.13–0.25; BS/DS= 0.43–0.60).

Antenna I relatively short (AL/BL = 0.10–0.14; AL/DA=3.0– 3.6 in adults), triangular in section; protruding greatly beyond tip of rostrum. Antennular sensory seta relatively short (about third of antenna I length), arising somewhat basally to antenna I middle ( Fig. 8J ). Nine bisegmented aesthetascs, with pointed teeth around them. No setules at anterior margin of antenna I. Numerous rows of minute denticles encircling antennular surface. Antenna II relatively short. On antenna II, spine situated on proximal segment of exopod somewhat shorter than length of second segment ( Fig.8K ). Setae 0-0-3/1-1-3; spines 1-0-1/0-0-1.

Limbs in general as in previous species ( Fig. 9A–J ). IDL of limb I with a remarkable strong hook-like seta, but not so large as in E. macracanthus , smallest seta very small, as in the latter ( Fig. 9A–B ). IDL with long distal spinules (about 11 in largest adults), long proximal spinules (8 in largest adults), short marginal spinules (6 in largest adults) and short basal spinules (10 in largest adults). On exopodite III seta 7 somewhat longer than seta 6 ( Fig. 9E ). On exopodite IV both setae 1 and 2 short ( Fig. 9G ). On exopodite V setae 5–6 slightly increasing in size basally. Filter plate of gnathobase III–V limbs with 8 setae.

Ephippial female. Body more compressed laterally, with median dorsal keel ( Fig. 8B–C ).

Male. Unknown

Length. 0.69–2.00 mm in our material, up to 3 mm according to Tanaka & Fujita (2002).

Comments. Smirnov (1998: p. 81) said that “Easternmost Siberia is also distinguished by the presence of ... an undescribed species of Eurycercus ”. As we found, this taxon has been formally described as E. nipponica Tanaka & Fujita, 2002 based on samples from Japan ( Tanaka & Fujita 2002). The author’s diagnosis was lacking any helpful information on the taxon discrimination from other species, but it is obvious from the author’s drawings and photos that: (1) the labral keel is very large and has an angled apex; (2) the head pores are located on a bubble-like projection (not represented by the authors in their drawings, but see in their photo in Plate 7 (fragment 1); (3) the preanal teeth on the pre-claw portion are mainly singular. After our redescription, it is clear that this is a valid species.

Distribution. E. nipponica was known from Japan ( Tanaka & Fujita 2002; Tanaka et al. 2004) – we found it also in Kamchatka (see Fig. 1 ). The species could be present in Sakhalin Island, Kurile Islands and, Chukotka Peninsula.

Ecology. Mostly, it is present in relatively large lakes and smaller water bodies associated with them (i.e. connected during a spring flooding time). The species is found in very shallow flooded grasslands, but, as in case of E. macracanthus , we think that it could be found in temporary water bodies only as the remains of a larger water body formed by spring flooding. It is present in the vegetation patches in rivers themselves.

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 8. Eurycercus nipponica, female from a swampy area (with a fresh bear trail in time of sampling) near Travianoy Cape, Kurilskoe Lake, Kamchatka Area, Russia A, parthenogenetic female, lateral view. B–C, ephippial female, lateral and anterior view. D, parthenogenetic female, ventral view. E, head. F, dorsal head pores. G, postabdomen. H, its distal portion. I, its basal portion. J, antenna I. K, antenna II. Scale bar denotes 1 mm (A–D); 0.1 mm (E–K).

FIGURE 9. Eurycercus nipponica, limbs of parthenogenetic female from a swampy area (with a fresh bear trail in time of sampling) near Travianoy Cape, Kurilskoe Lake, Kamchatka Area, Russia A, limb I. B, inner distal lobe of limb I. C, limb II. D, its distal armature. E, limb III. F, distal armature of its gnathobase. G, limb IV. H, distal armature of its gnathobase. I, limb V. J, limb VI. Scale bar denotes 0.1 mm.