Pseudepimeria Chevreux, 1912

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 : 119-121

Subgenus Pseudepimeria Chevreux, 1912

Pseudepimeria Chevreux, 1912: 216 (9 on reprints).

Pseudepimeria – Gurjanova 1955: 189, 190. — J.L. Barnard 1969: 396. — De Broyer 1983: 305 (discussion). — Coleman 1998a: 22 (discussion).

Type species

Pseudepimeria grandirostris Chevreux, 1912 .

Description

Body opaque, with teguments strongly calcified, very strongly ornamented and sculptured by teeth and carinae. Rostrum long. Eyes conical. Pleonites 1–3 and pereionites 1–7 with strong mid-dorsal tooth. Each pereionite is entirely lined by a strong and sharp transverse carina starting on the mid-dorsal tooth and terminating at the connection with coxa; these transverse carinae bear two pairs of small teeth: a dorsolateral one and a second one just above the connection with coxa. Pleonites 1–2 with one pair of well developed dorsolateral teeth and smaller teeth in various arrangement more ventrally; pleonite 3 with 3 pairs of dorsolateral teeth and smaller teeth in various arrangements more ventrally. Coxae 1–3 (and often coxa 4) with sharp tip. Coxae 1–3 sharply keeled along their axis. Coxa 4 with sharp carina starting at ventral tip of coxa and terminating at posterior tip of coxa; this carina sometimes bears a tooth or a lobe projecting laterally; carina very distant from posteroventral border of coxa at its deepest point; posteroventral border of coxa concave; anterior corner of coxa strongly bulging anteriorly and sometimes produced into a tooth. Coxa 5 with strong lateral carina which is laterally or posterolaterally produced into a tooth, which is sometimes very large. Coxa 6 with strong lateral carina which is laterally or posterolaterally produced into a tooth, which is much smaller than that of coxa 5. Posteroventral tooth of epimeral plate 3 strong to very strong. Dorsal process of urosomite 1 produced into a sharp tooth directed upwards. Urosomite 2 with pair of small teeth pointing upwards. Lateral borders of urosomite 3 posteriorly terminated into a sharp tooth or an acute angle. Peduncle of antenna 1 with teeth. Mandible with molar process triturative. Lower lip with narrow (V-shaped) hypopharyngeal gap. Palp of maxilliped with 4 articles. Gnathopods very small, achelate; gnathopod 2 distinctly more slender than gnathopod 1. Basis of pereiopods 5–6 broad, with strong posteroproximal protrusion (which can be acute but not sword-like and which is directed posteriorly) and posterodistal tooth projecting posteriorly. Posterior border of basis of pereiopod 7 with strong median angle followed by deep excavation, terminated into a tooth projecting posteriorly. Merus, carpus and propodus of pereiopods 3–7 very short and very stout; dactylus medium-sized, stout and strongly curved, partly folding on propodus (as if they were designed to clasp on the branches of bushy organisms). Benthic.

Body length

The maximum body length recorded in Pseudepimeria species ranges between 22 and 35 mm.

Ecology

Benthic, 50– 573 m.

Distribution

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

Remarks

Of all the Epimeria subgenera, Pseudepimeria is probably the most distinctive. Their highly sculptured and processiform body, and their strong clasping pereiopods 4–7 presumably reflect a specialized habitat. Hydroid remains were found in the stomach of E. (Pseudepimeria) oxicarinata ( Coleman 1990a) and pictures of this species clinging on hydroids have been published ( Coleman 2007). Coleman (1988) also observed E. grandirostris eating branches of hydroids in an aquarium on the RV Polarstern. Some species are morphologically very similar to each others, but the most similar forms appear to be allopatric. These complexes include the tetrad amoenitas / debroyeri / cf. debroyeri / pulchra and the triad callista / grandirostris / kharieis . Molecular data were not available for all taxa, hence some taxonomic decisions were taken based on morphology alone. Some observed morphological differences are possibly sizedependant, which did not facilitate taxonomic decisions (descriptions are based on adult females only). Immature specimens are assumed to be conspecific with adults of the most similar species found in the same region.

Key to the species of Pseudepimeria

This key applies to adult females only.

1. Mid-dorsal tooth of pereionite 1 short and not arching forward; mid-dorsal tooth of pereionite 2 equal or slightly shorter than mid-dorsal tooth of pereionite 1; mid-dorsal tooth of pereionites 3–7 and pleonites 1–2 blunt or not very sharp ………………………………………………………………2

– Mid-dorsal tooth of pereionite 1 long and arching forward; mid-dorsal tooth of pereionite 2 considerably shorter than mid-dorsal tooth of pereionite 1; mid-dorsal tooth of pereionites 3–7 and pleonites 1–2 very sharp, sword-like …………………………………… E. (Pseudepimeria) oxicarinata Coleman, 1990 [Elephant Island, North of Nelson Island (Drake Passage)]

2. Mid-dorsal tooth of pereionites 3–7 and pleonites 1–2 very large and narrow; mid-dorsal tooth of pereionite 1 with anterior border (nearly) straight and perpendicular to body axis; in dorsal view, carina of coxa 4 strongly protruding; in lateral view anterior corner of coxa 4 forming a lobe or tooth well separated (by deep notch) from anteroventral border; carina of coxa 5 posteriorly produced into a very strong tooth pointing obliquely backwards or laterally, of which the tip is narrow: E. (Pseudepimeria) pulchra complex ………………………………………………………3

– Mid-dorsal tooth of pereionites 3–7 and pleonites 1–2 medium-sized and fairly broad; mid-dorsal tooth of body segment 1 with anterior border convex and/or oblique with body axis; in dorsal view, carina of coxa 4 weakly protruding; in lateral view anterior corner of coxa 4 forming a low lobe poorly separated (by shallow concavity) from anteroventral border; carina of coxa 5 posteriorly produced into a strong to medium-sized tooth pointing backwards or obliquely backwards, of which the tip is broad: E. (Pseudepimeria) grandirostris complex …………………………………5

3. Pleonite 3 with broad to fairly broad triangular mid-dorsal tooth; carina of coxa 4 rounded in dorsal view; posterior border of third epimeral plate convex, curved, not produced into a tooth; gnathopod 1 with carpus and propodus of medium width; gnathopod 2 with carpus and propodus very slender …………………………………………………………………………………………4

– Pleonite 3 with long sword-like mid-dorsal tooth; carina of coxa 4 bluntly triangular in dorsal view; posterior border of third epimeral plate produced into a tooth; gnathopod 1 with carpus and propodus very robust; gnathopod 2 with carpus and propodus of medium width ……………………………… E. (Pseudepimeria) pulchra Coleman, 1990 [South Orkney Islands]

4. Pleonite 3 with very broad, blunt, triangular mid-dorsal tooth; posterior border of third epimeral plate forming a strongly protruding curved projection; tip of lateral carina of coxa 5 blunt (in dorsal view) …………… E. (Pseudepimeria) debroyeri sp. nov. [eastern and possibly western Weddell Sea]

– Pleonite 3 with fairly broad and acute-tipped mid-dorsal tooth; posterior border of third epimeral plate weakly curved; tip of lateral carina of coxa 5 sharp (in dorsal view)………… ……………………………………………… E. (Pseudepimeria) amoenitas sp. nov. [Adélie Coast]

5. Posteroproximal projection of basis of pereiopod 5 rounded; posterior border of basis of pereiopod 7 bluntly angulate in proximal 0.75 ………………………………………………………………6

– Posteroproximal projection of basis of pereiopod 5 acutely triangular; posterior border of basis of pereiopod 7 with rounded discontinuity in proximal 0.75 ……………………… E. (Pseudepimeria) grandirostris ( Chevreux, 1912) [Antarctic Peninsula and South Shetland Islands]

6. In dorsal view, lateral border carina of coxa 5 distinctly oblique; posteroproximal projection of basis of pereiopod 6 produced into a sharp triangular tooth; dactylus of gnathopod 2 very broad ……………………………………………… E. (Pseudepimeria) callista sp. nov. [Adélie Coast]

– In dorsal view, lateral border of carina of coxa 5 almost parallel to body axis; posteroproximal projection of basis of pereiopod 6 produced into a bluntly angulate lobe; dactylus of gnathopod 2 moderately broad ………… E. (Pseudepimeria) kharieis sp. nov. [Eastern Weddell Sea]