Subepimeria Bellan-Santini, 1972

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 : 140-141

Subgenus Subepimeria Bellan-Santini, 1972

Subepimeria Bellan-Santini, 1972: 225 .

Subepimeria – Karaman & J.L. Barnard 1979: 108 –109 (in part).

Type species

Subepimeria geodesiae Bellan-Santini, 1972 .

Description

Body opaque, with teguments moderately calcified. Rostrum medium-sized. Eyes not conical. Pleonite 2 posteriorly produced into a small sharp tooth oriented backwards; pleonite 1 and pereionite 7 sometimes also posteriorly produced into a tooth or bump; dorsal border of pleonite 3 keeled; in lateral view that keel posteriorly terminated into a rounded bump or a squared angle. With the exception of the aforementioned mid-dorsal ornamentations, pereionites and pleosomites perfectly smooth. Coxae 1–3 with blunt tip, not sharply keeled. Coxa 4 with indistinct carina starting at ventral tip of coxa and terminating at posterior tip of coxa; this carina remains very close to the posteroventral border of coxa, the space in-between forming a very shallow groove; posteroventral border of coxa 4 very weakly concave, nearly straight. Coxae 5–6 without tooth or distinct protrusion. Mid of posterior border of epimeral plates 1–3 not produced into a tooth. Posteroventral tooth of epimeral plate 3 medium-sized to strong. Dorsal process of urosomite 1 produced into a triangular tooth directed upwards. Urosomite 2 without pair of small teeth pointing upwards. Lateral borders of urosomite 3 posteriorly terminated into a sharp tooth or bluntly angular. Peduncle of antenna 1 without teeth or with dentition vestigial. Mandible with pars molar process triturative. Lower lip with narrow (V-shaped) hypopharyngeal gap. Palp of maxilliped with 4 articles. Gnathopods of normal size, with carpus and propodus of medium slenderness, with palm obliquely transverse but poorly developed (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, with posteroproximal rounded protrusion (sometimes very weak and scarcely distinct); a posterodistal tooth projecting posteriorly can be present on basis of pereiopod 5, otherwise basis posterodistally angulate or bluntly angulate. Posterior border of basis of pereiopod 7 slightly convex in proximal 0.8; at this level there is a slight angular discontinuity and the distal 0.2 can be slightly concave; posterior border terminated into a blunt angle or a blunt tooth directed in the axis of the basis. Dactylus of pereiopods 5–7 short. Benthic. Small species.

Body length

The maximum body length recorded in Subepimeria species ranges between 14 and 16 mm.

Ecology.

Benthic, 52– 840 m.

Distribution

Circum-Antarctic, as far north as South Georgia.

Remarks

Molecular data (COI, 28S) ( Verheye et al. 2016a) indicate that Subepimeria and Drakepimeria are sister clades ( Fig. 342 ). The morphology of their gnathopods and pereiopods is similar. However, Subepimeria species are much smaller (<20 mm) and have only one or two (smaller) mid-dorsal teeth and no dorsolateral teeth on pereionites and pleosomites. The lateral carina of coxa 4 is also vestigial in Subepimeria , whilst it is very strongly developed in Drakepimeria . We believe that these conspicuous morphological differences justify the recognition of distinct subgenera for these clades.The morphological identification of species within the subgenus Subepimeria is very difficult. Interspecific differences are based on ill-defined characters, such as the curves of coxa 4. The species are also rare, which largely prevents the study of individual and allometric differences within species. The link between immatures and adult specimens of Epimeria (Subepimeria) iota is tentative as only immature specimens were available for sequencing. As Subepimeria species can only be distinguished by a combination of illdefined characters, we delineate their differences in a tabular format ( Table 1 ) instead of an identification key.

Figures

Fig. 342. Phylogenetic tree obtained by Bayesian analysis of the concatenated COI and 28S sequences, updated from Verheye et al. (2016). Bayesian posterior probabilities and bootstrap values (from the Maximum Likelihood analysis) are indicated above the nodes of interest. Bootstrap values inferior to 50 are not indicated. Besides the species names are indicated the MOTUs codes used in Verheye et al. (2016). The Genbank accession number of the outgroup species: Gnathiphimedia sexdentata (Schellenberg, 1926) are KU870835 (COI) and KU759609 (28S).