Metopa stelleri Shoemaker, 1964

Tandberg, Anne Helene S., 2009, A redescription of Metopa species (Amphipoda, Stenothoidae) based on the type material. 2. The United States National Museum of Natural History (NMNH), Zootaxa 2309, pp. 43-68 : 62-67

Metopa stelleri Shoemaker, 1964

Metopa stelleri Shoemaker 1964: 394 –396, fig.2

Type locality: Cape Rollin, Simushir Island, Kurile Islands. 419m ( Shoemaker, 1964)

Material examined. Morphological examination: 7 mm male from Alb. Sta. 4803 (46°42’ N, 151°45’ E), June 24, 1906, 229 fath. (419 m) Cape Rodhin, Simshir Island (Kurile islands, Russia). This is the type locality, paratypes have been examined (from the same station as the type). These were also used in the 1964 paper from Shoemaker, the figures were made in 1952)

See figures 15, 16, 17 and 18.

Morphological description. Male, 7mm, paratype.

Head ( Fig. 15 ): epistome small and rounded; cephalic lobe rounded; eye 1/3 of head length, round, well defined. Antenna 1 ( Fig. 15 ): half length of body, slender; peduncle subequal in length to flagellum; flagellum 16-articulate, naked; no accessory flagellum observed. Antenna 2 ( Fig. 15 ): slightly longer than A1; slender; peduncle article 4 slightly longer than article 5; flagellum subequal to peduncle article 5, 12-articulate. Labium ( Fig. 16 ): round; short simple setae at apex. Mandible ( Fig. 16 ): palp 3-articulate, article 3 very small, article 2 elongate, cross-section circular; right mandible with lacinia mobilis broadly serrate with one tooth at inner margin; incisor serrate and well defined on both sides; 15 strong, serrate raker setae, no molar. Maxilla 1 ( Fig. 16 ): inner plate naked and small; outer plate with six strong (two of which are serrate) setae and one tooth, a series of simple setae along inner margin, palp 2x length of outer plate, 1-articulate, one tooth and one strong seta at apex, serrate with a row of shorter setae along inner margin, several simple setae on palp face. Maxilla 2 ( Fig. 16 ): outer plate in normal position to inner plate, inner plate somewhat shortened, outer plate setose (37 simple setae), inner plate with four long and several shorter simple setae. Labrum ( Fig. 16 ): rounded; bilobed. Maxilliped ( Fig. 16 ): long and slender; inner plates partly divided, one small and one slightly longer simple seta on distal margin; outer plate very small, reaching 1/8 of palp article 1 length; palp 4-articulate, article 3 with thin cushion of short simple setae distally; article 4 with a dense row of short simple setae along inner margin.

Pereon: pereonites 1–5 dorsally smooth, pereonites 6 and 7 and pleon segments 1 and 2 produced dorsally into backward-pointing teeth, forming a small carina. Gnathopod 1 ( Fig. 17 ): subchelate; coxa very small and subquadrate; basis linear, distal anterior margin with long simple setae; ischium subquadrate; merus not distally free, a thick cushion of simple short setae at posterodistal margin, several longish simple setae at distal margin; carpus longish, several long simple setae at posterior margin; propodus as long and wide as carpus, two rows of simple setae along anterior margin, palm oblique, almost transverse, smooth with short simple setae, palmar corner rounded, posterior margin longer than palm; dactylus smooth with flat inner margin (3– dimensional) covered with a thick row of short setae, as long as palm, very slightly curved. Gnathopod 2 ( Fig. 17 ): coxa covering coxa 1, suboval, pointing forwards; basis linear, a row of simple setae along anterior "keel" (basis having a triangular cross-section); ischium short with simple setae along posterior margin; merus subtriangular, few simple setae at distal margin; carpus short, posterodistal margin with a patch of flat, short setae forming a flat cushion around posterodistal margin, a row of simple setae along distal margin; propodus elongate and slightly broader than carpus, suboval, palm oblique and crenulate with a large excavation near palmar corner, forming a tooth, posterior margin as long as palm; dactylus smooth with flat inner margin with row of tiny setae, curved, reaching tooth of palm. Pereopod 3 ( Fig. 17 ): coxa subrectangular; rest of leg slender, long and simple, almost naked; propodus 3x dacylus; dactylus with serrate posterior margin. Pereopod 4 ( Fig. 17 ): coxa subtriangular, ventral margin convex; rest of leg slender, thicker than P3; carpus and propodus with short groups of several setae along posterior margin, dactylus with serrate posterior margin, reaching 0.5x propodus. Pereopod 5 ( Fig. 18 ): coxa small; basis linear; meral lobe reaching 0.5x carpus; dactylus reaching 0.5 propodus, serrate anterior margin; basis and merus with short simple setae along posterior margins, carpus and propodus with brushes of groups of three simple setae along anterior margins. Pereopods 6 and 7 ( Fig. 18 ): coxae small; bases posteriorly expanded; meral lobe reaching 0.7x and 0.8x carpus, respectively, simple short setae along posterior and anterior margins; carpus and propodus with brushes of 3 simple setae along anterior margins; dactyli with serrate anterior margins, reaching less than 1/2 length of propodus.

Urosome ( Fig. 18 ): smooth. Epimeral plate 3 ( Fig. 18 ): rounded sharp angle. Uropod 1 ( Fig. 18 ): longer than uropod 2; biramous; peduncle longer than rami, several short simple setae along outer margin; rami subequal. Uropod 2 ( Fig. 18 ): longer than uropod 3; biramous; peduncle longer than rami, row of short simple setae along outer margin; inner ramus longer than outer ramus, few short simple setae on inner ramus. Uropod 3 ( Fig. 18 ): uniramous, peduncle longer than ramus, row of simple setae along outer margin; ramus 2- articulate, articles subequal, one seta at inner article. Telson ( Fig. 18 ): round, somewhat boat-shaped; four pairs of robust and one pair of small setae.

Shoemaker (1964) mentions that the female is very like the male, but with shorter antennae. He further proposes this species to be close to Metopa cristata , from which it differs in the lack of dorsal teeth on pereon segments 1–5.

Ecology: we know nothing about the ecology.

Distribution: this is only known from the type locality and the nearby Albatross station 4804 (4642’ N, 151 47 ’E) both by the Kurile Islands, both at around 400m depths.

Figures

FIGURE 15. Metopa stelleri Shoemaker, 1964, paratype, male, 7 mm, Albatross st. 4803: whole animal. Scale bar is 0.5 mm.

FIGURE 16. Metopa stelleri Shoemaker, 1964, paratype, male, 7 mm, Albatross st. 4803: labrum, right and left mandible, labium, maxilla 1, maxilla 2, maxilliped. all scale bars are 0.1 mm.

FIGURE 17. Metopa stelleri Shoemaker, 1964, paratype, male, 7 mm, Albatross st. 4803: gnathopod 1, gnathopod 2, pereopod 3, pereopod 4. All scale bars are 0.1 mm.

FIGURE 18. Metopa stelleri Shoemaker, 1964, paratype, male, 7 mm, Albatross st. 4803: pereopod 5, pereopod 6, pereopod 7, telson, urosome. All scale bars are 0.1 mm.