Eurycercus nigracanthus Hann 1990

Eurycercus nigracanthus Hann, 1990

(Figs 4–5)

Eurycercus (Teretifrons) sp. in Frey & Hann 1985, P. 327.

Eurycercus nigracanthus Hann 1990, P. 2150, Figs 16–40; Bekker 2012, P. 125–130, Figs 41–42.

Type locality. “ Weiss Pond, Avalon Peninsula, Newfoundland, Canada ” (Hann 1990). Unfortunately, the coordinates represented by Hann (1990) are apparently wrong.

Type material. Holotype. Parthenogenetic female, USNM 243306.

Paratypes. 2 adult males, USNM 243307. 2 juvenile males (instar II) USNM 243308. 2 juvenile males (instar I), USNM 243309. 2 parthenogenetic females, USNM 243310.

Other material examined here. All from Newfoundland and Labrador, Canada: 20 parthenogenetic ♀♀ from Oxen Pond (appr. N47.5713°, W52.7623°), coll. in 28.08.1984 by D.G. Frey, DGF 7051. 14 parthenogenetic ♀♀ from Round Pond (appr. N47.7°, W52.81°), N of St. Johnes, coll. in 28.08.1984 by D.G. Frey, DGF 7055. 7 parthenogenetic ♀♀ from Pond along Hgy 1. (appr. N47.36°, W53.05°), 1.5 miles S of Butterpot Provincial Park, coll. in 0 5.09.1984 by D.G. Frey, DGF 7109. 5 parthenogenetic ♀♀ from Fen Pool (appr. N46.88°, W54.11°), East side of road from Cape St. Marys to Hgy 100, coll. in 11.091984 by D.G. Frey, DGF 7135a–b. 22 parthenogenetic ♀♀ from a water body (appr. N47.6°, W52.7°) near Hgy. 1 opposite truck weighing station W of St. John's, coll. in 0 9.1984 by D.G. Frey, DGF 7167- II. 45 parthenogenetic ♀♀ from Pond-G (N49.4931°, W56.4655°), coll. in 30.06.2005 by L.J. Hovind & M. Faustova, DJT 20-115, AAK M-1177, and AAK M-0536.

Diagnosis. In lateral view body sub-ovoid (Fig. 4 A), maximum height of the body in its middle portion (BH/ BL= 0.64–0.74; VL/BL=0.80–0.89). In anterior of dorsal view, body not compressed laterally, median dorsal keel absent (Fig. 4 B–C). Rostrum relatively long (Fig. 4 D). Ocellus small. Dorsal head pores located on a pancake-like projection on dorsal margin of head and slightly protrude beyond the edge of the head shield (Fig. 4 E). Lateral head pores small and subcircular (Fig. 4 F). Labrum with a large median keel, with angled apex, projecting beyond distal end of antenna I (Fig. 4 D). Armature of valve margin as in other species (Fig. 4 G–I). Postabdomen large (PL/BL= 0.41–0.45), relatively broad (PH /PL= 0.46–0.54) with almost parallel ventral and dorsal margin (Fig. 5 A) and deep embayment (Fig. 5 B). Preanal teeth more elongated, pointed (NT=118–121), in most cases dark, strongly chitinized; rudimentary teeth up to bases of postabdominal setae (Fig. 5 C). Teeth in distal part of postanal margin large, long, predominantly double (Fig. 5 B). Teeth in distal part of anal margin – proximal part of postanal margin short, almost all of them single. Postabdominal claw relatively robust (CL/PL=0. 23–0.26) with two basal spines (DS/CL=0.28–0.30; BS/CL=0.11; BS/DS=0.40–0.50). Antenna I elongated (AL/BL=0.10–0.11; AL/DA=4.67– 4.87); antennular sensory seta arising in antenna I distal part (Fig. 5 D). Numerous short rows of minute denticles encircling antennular surface. On antenna II spine situated on proximal segment of exopod equal in length or slightly longer than second segment (Fig. 5 E). IDL of limb I supplied three bisegmented setae, one of them a relatively strong hook-like seta, its diameter at base equal or slightly more than diameter at base of longest setae IDL (Fig. 5 F). The smallest of the three setae relatively short, its length two or more times less than longest setae IDL. IDL with groups of spinulae: 10–12 long distal spinulae; 11–15 long proximal spinulae and 7–10 very short basal spinulae; marginal spinulae absent (Fig. 5 F). Eight setae in filter plate II, 10 setae in filter plate III; 9–10 setae in filter plate IV, 8–9 setae in filter plate V. Exopodite IV with 8 setae; exopodite V with 8 setae. Intestine with a double loop, posterior intestinal caecum absent.

Ephippial female and ephippum. Slight median keel on valves, whole valves are involved in ephippium formation. Ephippia in our fixed material were almost unpigmented additionally as compared with parthenogenetic female.

Adult male. As in other species of the subgenus, see Hann (1990).

Size. Juvenile and adult parthenogenetic females in our material 2.3–4.5 mm. Juvenile females 1.2–3.2 mm, adult parthenogenetic females 3.7–5.8 mm, adult males 1.8–2.1 mm (Hann, 1990).

Differential diagnisis. Among the species of Eurycercus (Teretifrons), E. nigracanthus is unique having a ring of major head pore projects above head shield, but no projection in middle of major head pore. In contrast to E. chernovi sp.nov., it has 10 setae in exopodite IV and 8 setae in exopodite V.

Distribution. It is found in Labrador and Newfoundland, Cape Breton Island and Nova Scotia (Hann 1990). But a real range of its distribution in North America is not clear, i.e. see below. Comments. The species was adequately described by Hann (1990) except few details which are discussed below.