Epimeria (Drakepimeria) cleo
Verheye, Marie L., Lörz, Anne-Nina & D‘Acoz, Cédric D’Udekem, 2018, Epimeria cleo sp. nov., a new crested amphipod from the Ross Sea, Antarctica, with notes on its phylogenetic affinities (Crustacea, Amphipoda, Eusiroidea, Epimeriidae), Zootaxa 4369 (2), pp. 186-196: 187-194
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|Epimeria (Drakepimeria) cleo|
Epimeria (Drakepimeria) cleo sp. nov.
Epimeria (Drakepimeria) sp. 1.— d'Udekem d'Acoz & Verheye 2017: 21, 65.
Etymology. Epimeria cleo sp. nov. is dedicated to the daughter of the first author, who was born during the preparation of this manuscript. The name is a noun in apposition.
Description. Head: rostrum as long as head, overreaching distal margin of the first article of antenna 1; eye oval, 0.4 x head height.
Pereonites: pereonite 1 subequal in length to head (excluding rostrum), pereonite 2 0.7 x length of pereonite 1, pereonites 1 and 2 lacking mid-dorsal process, bearing apically rounded weak carinate lateral projection; pereonites 3–7 with size-increasing, low mid-dorsal tooth (that of pereonite 2 nearly reduced to a bump); pereonites 3 to 5 bearing mid-lateral carinate projection (apically rounded in pereonite 3–4, apically acute or subacute in pereonite 5); pereonites 6 and 7 with sharp mid-lateral tooth.
Pleosome: pleonites 1–3 with low mid-dorsal tooth (anteriorly regularly rounded) and mid-lateral tooth. Middorsal tooth of pleonite 3 with very weak median notch (and with trace of a second notch on distal edge). Epimeral plates 1–3 anteroventral angle rounded, posteroventral angle produced into a strong tooth.
Urosome: urosomite 1 with sharp triangular mid-dorsal tooth; urosomite 2 shortest, dorsolaterally smooth; urosomite 3 middorsally smooth, dorsolateral angle produced into a small triangular tooth.
Antenna 1 ( Fig. 2A–BView FIGURE 2): article 1 of peduncle about 2 x as long as article 2, 3 x as long as article 3, with distolateral tooth (1a) not reaching mid of article 2 (teeth excluded), with distomedial tooth (1b) not reaching mid of article 2 (teeth excluded), with major ventral tooth (1c) almost reaching half of article 2 (teeth excluded) and a second (half the length) ventral tooth (1d) more medially. Article 2 of peduncle about 2 x as long as article 3, with lateral (2a) and medial (2b) teeth overreaching corpus of article 3 and reaching mid of ventral tooth of article 3; with two subequal ventral teeth (2c–d) (parallel and very close to each other) and slightly overreaching corpus of article 3. Article 3 with ventral tooth (3) about as long as corpus of article. Accessory flagellum scale like, reaching distal end of first flagellar article; primary flagellum with 44 articles; flagella scarcely setose.
Antenna 2: article 4 of peduncle slightly longer than article 5, with distolateral denticle; flagellum with 66 articles.
Labrum: with very short distal hair-like setae at both sides of terminal notch.
Hypopharynx: lobes broad, distally and medially covered with hair-like setae, lateral process narrow, rounded.
Mandible: incisor with 4 blunt teeth, molar produced and triturative; palp article 1 non-setose, article 2 setose medially, article 3 densely setose medially, with 4 long setae distally.
Maxilla 1: inner plate subtriangular, obliquely convex inner margin with 14 stout plumose setae; outer plate distal margin oblique, with 11 lobate robust setae; palp exceeding outer plate, palp article 1 short, article 2 curved medially with 7 robust setae distomedially and 5 slender setae behind them.
Maxilla 2: with long, slender setae distally on lateral and medial plates.
Maxilliped: outer plate broadly rounded distally, reaching mid length of second article of maxillipedal palp; inner plate with row of long setae medially and anteriorly; palp medial margin strongly setose, propodus with groups of long setae reaching distal end of dactylus (two groups of setae forming transverse rows).
Gnathopod 1: coxa long, slender, anterior margin with slight angular discontinuity at distal 0.2, distally pointed, longitudinal mid lateral ridge well developed; basis linear, slender, both margins with slender setae; merus slightly longer than ischium, anterior margin very short, distal margin oblique, posterodistal angle acute, setose; carpus slightly expanding at distal end, posterior margin strongly setose, anterodistal margin with group of long setae; propodus margins convex, posterior margin and palm lined with robust setae, palm oblique; dactylus slender, slightly curved, posterior margin minutely serrated.
Gnathopod 2: coxa 2 wider and longer than coxa 1, with lateral ridge, pointed; basis linear; ischium and merus similar to gnathopod 1; carpus linear and more elongated than in gnathopod 1, strongly setose posterior margin; propodus very similar to that of gnathopod 1 but slightly more elongated; dactylus similar to that of gnathopod 1.
Pereopod 3: coxa 3 longer than coxa 2, with midlateral ridge, pointed; basis linear, slender setae on anterior and posterior margins; merus, carpus and propodus very robust; merus and carpus slightly expanded distally; carpus 0.6 length of merus; propodus 0.8 length of merus; carpus, merus and propodus with robust setae on posterior margin, anteriorly nearly naked except robust seta on anterodistal corner; dactylus stout, without setae and curved.
Pereopod 4: coxa 4. Anterodorsal border nearly straight and of normal length; anteroventral border nearly straight (inconspicuously convex) and of normal length; a low and long curve forms a very gradual transition between the anterodorsal and anteroventral borders; ventral tooth long, slender, apically acute and oriented backwards; lateral carina without tooth or angularity, not projecting laterally, carina very distant from margin of coxa at its deepest point; basis to dactylus as for pereopod 3.
Pereopod 5: coxa with posterodistal corner strongly produced, drawn out to pointed wing in dorsal view; basis anterior margin straight, setose, posterior margin slightly expanded proximally, with posterodistal corner produced into an acutely triangular tooth, with ridge along entire length of basis; ischium anterodistal margin pointed; merus, carpus and propodus very robust; merus with posterior margin produced; carpus about as long as merus, with anterior margin setose; dactylus stout, curved.
Pereopod 6: coxa with carinate, lateral tooth, forming a triangular wing in dorsal view; posteroventral corner broadly rounded; basis to dactylus as for pereopod 5.
Pereopod 7: coxa subrectangular, with low lateral carina, with posterodistal corner bluntly angular; basis larger than that of pereopod 6, posteriorly weakly sigmoid, with posterodistal corner produced into a small tooth; ischium to dactylus as for pereopod 5 and 6.
Pleopods: pleopods 1–3 with two rami each; inner and outer rami subequal, twice as long as peduncle.
Uropod 1: peduncle slightly longer than rami; rami subequal in length, margins with short robust setae.
Uropod 2: peduncle naked, 0.9 x length of outer ramus; inner ramus 1.3 x outer ramus; both rami outer and inner margin with short robust setae.
Uropod 3: peduncle short, half length of outer ramus, peduncle mid dorsal ridge, drawn out in 3 pointed processes; inner margin of both rami with sparse robust setae.
Telson: 1.2 longer than wide, with narrow V-shaped cleft third of length, lobes triangular.
Variation. In dorsal view, males with pereon narrower than in females.
Body length. 30–52 mm.
Type locality. Western Ross Sea
Distribution. Southern Ocean: western Ross Sea, 151– 409 m.
Taxonomic remarks. E. cleo sp. nov. belongs to the subgenus Drakepimeria d'Udekem d'Acoz & Verheye, 2017, which is a morphologically homogeneous Epimeria species complex from the Southern Ocean that also includes E. macrodonta Walker, 1906 , E. reoproi Lörz & Coleman, 2001 , E. schiaparelli Lörz, Maas, Linse & Fenwick, 2007 , E. similis Chevreux, 1912 , E. vaderi Coleman, 1998 and 11 new species described by d'Udekem d'Acoz & Verheye (2017). Epimeria cleo sp. nov. is treated as Epimeria sp. 1 in the key to the Drakepimeria of the latter monograph. In all species of this subgenus, several pereon body segments and all pleosome segments bear a sharp, acute-tiped, dorsolaterally strongly flattened carinated tooth, arching posteriorly. In previous molecular phylogenies, all studied species were shown to form a clade ( Verheye et al. 2016; Lörz et al. 2007).
The subgenus Drakepimeria can be divided into two phenotypic groups. Group 1 includes those with a pair of small teeth pointing upwards on urosomite 2. Group 2 includes those which have no such teeth. Epimeria cleo sp. nov. belongs to that group 2. Group 2 includes species with 3 morphotypes of coxa 4 as seen in dorsal view: (A) those with the lateral carina presenting a tooth projecting laterally; (B) those with the lateral carina presenting an obtuse angle (but no real tooth) and (C) those with the carina looking perfectly smooth or with a low rounded (not angular) protrusion. Epimeria cleo sp. nov. belongs to that category 2C, along with Epimeria leukhoplites d'Udekem d'Acoz & Verheye, 2017 , E. robertiana d'Udekem d'Acoz & Verheye, 2017 and Epimeria vaderi Coleman, 1998 . E. robertiana is a deep-sea species found below 2000 m, and it departs from all species of the subgenus Drakepimeria by the shape of the dorsal projection of its urosomite 1, which points backwards instead of upwards.
Biology. Epimeria cleo sp. nov. appears to be iteroparous. Indeed, within the maxilliped of the holotype, which was a mature female with fully developed and setigerous oostegites, the outline of a new cuticle bordered with spines and setae in development could be observed. This indicates that the specimen was preparing an extra moult, after a presumably fertile intermoult.
Phylogenetic tree. A Bayesian tree of 34 specimens from the subgenus Drakepimeria was reconstructed based on a 1120 bp alignment (substitution model: GTR + I + G). E. cleo is shown to be nested within the clade composed of E. similis and 9 species, morphologically similar to E. similis and E. macrodonta ( Fig. 6View FIGURE 6) ( Verheye et al. 2016).
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