Epimeriella Walker, 1906

d’Acoz, Cédric d’Udekem & Verheye, Marie L., 2017, Epimeria of the Southern Ocean with notes on their relatives (Crustacea, Amphipoda, Eusiroidea), European Journal of Taxonomy 359, pp. 1-553 : 67-68

Subgenus Epimeriella Walker, 1906

Epimeriella Walker, 1906: 17 (in part).

Epimeriella – Gurjanova 1955: 189, 206 (in part). — J.L. Barnard 1961: 102 (in part); 1969: 161, 395 (in part). — McCain 1971: 160 (in part). — Karaman & J.L. Barnard 1979: 109 –110 (in part). — Holman & Watling 1983: 31 (in part, discussion). — Andres & Lott 1986: 131–136 (in part). — J.L. Barnard & Karaman 1991: 380, 394, 702 (in part). — Coleman 1998b: 215 (in part); 2007: 56 (in part). — Lörz & Brandt 2004: 179, 184, 188, 189 (in part).

Type species

Epimeriella macronyx Walker, 1906 .

Description

Body pellucid with teguments very weakly calcified. Rostrum minute (not reaching 0.2 of length of article 1 of peduncle of antenna 1), reduced to a narrow tiny blade-shaped process separating the bases of the first articles. Ventral lobe of head rounded. Eyes present, extremely large, not conical. Pereionite 7 and pleonites 1–3 with or without small posterodorsal tooth directed backwards; all pereionites and pleonites without dorsolateral pair of teeth, swelling or carina. Pereionites 1–7 without tooth or protrusion just above connection with coxa. Coxae 1–3 with rounded tip; coxa 4 with tip of variable sharpness. Coxae 1–3 not keeled or not strongly keeled along their axis. Coxa 4 narrow, not carinate; posteroventral border straight or very weakly concave. Coxae 5–6 without tooth. Mid of posterior border of epimeral plates 1–3 not produced into a tooth. Posteroventral tooth of epimeral plate 3 very small. Dorsal process of urosomite 1 produced into a low rounded process or into a carina posteriorly terminated in tooth directed backwards. Urosomite 2 without pair of small teeth pointing upwards. Lateral borders of urosomite 3 posteriorly terminated into an acute angle. Telson deeply cleft. Peduncle of antenna 1 with dentition very reduced (tiny ventral denticles may be present). Mandible with molar process drawn out, without triturative surface. Lower lip with wide hypopharyngeal gap. Palp of maxilliped with 4 articles. Gnathopods of normal size, with carpus and propodus broad to very broad, with palm obliquely transverse (gnathopods subcheliform); propodus not expanded distally; posterior border of dactylus lined by row of small oblique slender teeth. Basis of pereiopods 5–6 moderately broad, without posteroproximal protrusion or tooth and without posterodistal tooth projecting posteriorly. Posterior border of basis of pereiopod 7 convex along all its length, with tip angular or rounded. Dactylus of pereiopods 5–7 long to very long.

Body length

The maximum body length recorded in Epimeriella species ranges between 8 and 28 mm.

Ecology

Epimeria (Epimeriella) macronyx is obviously pelagic, as it is usually found in plankton nets. The fragile and poorly caclified morphology of other species suggest that they might also be pelagic or semipelagic. 0–1200 m.

Distribution

Circum-Antarctic, as far north as the South Orkney Islands.

Remarks

Epimeriella was initially erected as a genus ( Walker 1906), on the basis of the non triturative molar process of the mandibles. This character is considered as a synapomorphy since Epimeriella sensu Walker, 1906 forms a clade in our phylogenetic trees. It is herein split into two subgenera corresponding to two sub-clades with very different morphotypes. The robust benthic forms of the group walkeri are now placed into the new subgenus Laevepimeria subgen. nov. Only the slender pelagic or semipelagic forms ( Epimeria macronyx , E. scabrosa and their relatives) are retained within the subgenus Epimeriella . The extralimital species Epimeria pelagica Birstein & Vinogradov, 1958 also exhibits adaptations to a pelagic lifestyle: enlarged eyes and elongation of the posterior pereiopods ( Birstein & Vinogradov 1958). However, this species exhibits many other characters not observed in Epimeriella species such as the shape of the mandible.

Key to the species of Epimeriella

1. Pleonites 1–3 (and sometimes pereionite 7) with small posterodorsal tooth; dorsal process of urosomite 1 not produced into a tooth ………………………………………………………………2

– Pleonites 1–3 without posterodorsal tooth; dorsal process of urosomite 1 posteriorly produced into a tooth directed backwards …………………………………… Epimeria (Epimeriella) macronyx ( Walker, 1906) [Antarctic Peninsula to Ross Sea, usually caught in plankton nets]

2. Pereionite 7 with posterodorsal tooth; eye broadly elliptic; coxa 4 fairly wide, ventrally produced into a blunt angle ………………………......…… E. (Epimeriella) atalanta sp. nov. [Weddell Sea]

– Pereionite 7 without posterodorsal tooth; eye narrowly elliptic; coxa 4 fairly wide, ventrally pointed ………………………….........…… E. (Epimeriella) scabrosa (K.H. Barnard, 1930) [Oates Coast]

– Pereionite 7 without posterodorsal tooth; eye broadly elliptic; coxa 4 slender, ventrally rounded ………………………… E. (Epimeriella) truncata ( Andres, 1985) [west of Antarctic Peninsula]