Metopa spinicoxa Shoemaker,1955

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 : 58-62

Metopa spinicoxa Shoemaker,1955

Metopa spinicoxa Shoemaker 1955: 20 –22, fig 6 g –o

Type locality: off Point Barrow, Alaska ( Shoemaker, 1955)

Material examined. Morphological examination: NMNH 96250, Type. Male (6mm). "off Point Barrow base, Alaska. 175 feet (53m), 4 miles (6.5km) out, Oct 14, 1949 ".

See figures 12, 13 and 14.

Morphological description. Male, 6mm. (Type)

Head ( Fig. 12 ): small; epistome pointed (Shoemaker says "prominent, projected forward and cleft in the center by a deep sinus"); eyes approximately 1/3 head length, round and well defined. Antenna 1 ( Fig. 12 ): shorter than in the other species described here, reaching about 0.5x body length; peduncle article 1 barely longer than head; article 2 shorter than article 1; no accessory flagellum observed; flagellum subequal to peduncle, 14-articulate, each article with two simple short setae distally. Antenna 2 ( Fig. 12 ): slightly longer than antenna 1; peduncle strong, 2.5x length of flagellum, article 4 longer than article 5; flagellum 10- articulate. Mandible ( Fig. 12 ): mandibular palp 2-articulate, article 1 short and "round", article 2 long and slender with several simple setae; cross-section circular; incisor and lacinia mobilis serrate and well developed, a strong row of 10 raker setae; no molar. Maxilla 1 ( Fig. 12 ): inner plate with one simple seta; outer plate with three serrate and one conate setae, one pointed tooth and two rows of simple setae along inner margin and along distal margin; palp 1-articulate, weakly serrate with one short and one long simple seta for each serration, small tooth at apex, 2x length of outer plate. Maxilla 2 ( Fig. 12 ): outer plate somewhat at normal position to inner plate, inner plate shortened, inner plate with one type A seta and five simple setae, outer plate with nine simple setae. Labrum ( Fig. 12 ): rounded; bilobate; weakly asymmetrical. Maxilliped ( Fig. 12 ): long and slim; inner plate well separated, several short simple setae at distal margin; outer plate short and thin, reaching 1/4 of palp article 1; palp 4-articulate, several simple setae along inner margin, few very thin simple setae along outer margin; article 3 with a thin cushion of short setae at distal margin and three type A setae, article 4 3-dimensional, thick row of short setae along the inner "flat" margin.

Pereon: smooth. Gnathopod 1 ( Fig. 13 ): simple; coxa subquadrate; basis linear and naked; ischium subquadrate; merus distal margin nearly free, a cushion of simple setae along distal posterior margin, and six simple longer setae apically; carpus long and rectangular, a row of long simple setae on posterior margin; propodus slightly longer and thinner than carpus, narrowing at distal end, no palm, few long simple setae along straight posterior margin; dactylus reaching approximately 0.5x propodus, simple but strong, a row of strong short setae along inner/posterior margin, very weakly curved. Gnathopod 2: missing on type. Pereopod 3 ( Fig. 13 ): long and slender; coxa subrectangular, short simple setae along posterior distal margin; rest of leg simple with few but strong simple setae sparsely spread along posterior margins of merus, carpus and propodus; dactylus reaching 0.5x propodus, simple, curved at distal margin, naked. Pereopod 4 ( Fig. 13 ): coxa subtriangular, ventral margin rounded; rest of leg slender, double sets of strong setae along posterior margins of carpus and propodus; dactylus naked and simple, curved, reaching 0.5x propodus length. Pereopod 5 ( Fig. 14 ): coxa small and weakly elongated posteriorly; basis slender; meral lobe reaching 0.5x carpus; dactylus reaching 0.7x propodus, naked and weakly curved; merus to propodus with double set of strong simple setae at anterior margin, merus with simple setae also at posterior margin. Pereopods 6 and 7 ( Fig. 14 ): coxae small; basis posteriorly expanded, short strong setae along posterior margin; meral lobe as long as carpus on both legs, double sets of short simple setae along both margins; dactyli approximately 0.6–0.7 x propodus length, simple and smooth, weakly curved.

Urosome ( Fig. 14 ): smooth. Epimeral plate 3 ( Fig. 14 ): rounded, margins at right angles to each other. Uropod 1 ( Fig. 14 ): longer than uropod 2; peduncle longer than rami, several short simple setae along outer margin; biramous, rami subequal, three strong setae around basis of inner ramus. Uropod 2 ( Fig. 14 ): longer than uropod 3; biramous; peduncle subequal to inner ramus, inner ramus longer than outer ramus; peduncle with few simple setae, rami naked. Uropod 3 ( Fig. 14 ): uniramous, ramus with two articles; peduncle with five strong setae, ramus inner article with one seta. Telson ( Fig. 14 ): toungeshaped, elongate; flat; three pairs of robust setae.

Ecology: we have no notion about the ecology of this species. Shoemaker (1955) mentions females to be very similar to males, only a little smaller, and with shorter antennae.

Distribution: only known from type locality

Remarks: Shoemaker (1955) mentions this species to be very close to Metopa bruzelii ( Goës, 1866) as it is figured in Sars (1890-95), but a little "stouter", especially gnathopod 2, which must have been taken out for special examination and is missing in the type. Because gnathopod 2 was missing in the examined specimen, the original description from Shoemaker (1955) is included here: "Gnathopod 2 moderately developed; sixth joint a little wider than the fifth and a little shorter than the second, front and hind margins slightly convex, and widest in the middle; palm oblique, a little shorter than hind margin of joint, convex, bearing low wavy teeth, the central one of which is the largest, defined by an angular process adjacent to which is a shallow sinus bearing a spine; seventh joint fitting palm and bearing a row of spinules on inner margin." Shoemaker further mentions this gnathopod to be more robust than in Metopa bruzelii , the palm of M. bruzelii being smooth and not having a sinus adjacent to the defining angle. Shoemaker (1955) further mentions a 3- articulate mandibular palp, here it is described as two-articulate, but this character seems to be a plastic character in the genus Metopa ( Tandberg & Vader 2009) .

Figures

FIGURE 12. Metopa spinicoxa Shoemaker, 1955, type (NMNH 96250), male, 6 mm: head, mandible, maxilla 2, maxilla 2, labrum, maxilliped. All scale bars are 0.1 mm.

FIGURE 13. Metopa spinicoxa Shoemaker, 1955, type (NMNH 96250), male, 6 mm: gnathopod 1, pereopod 3, pereopod 4. All scale bars are 0.1 mm.

FIGURE 14. Metopa spinicoxa Shoemaker, 1955, type (NMNH 96250), male, 6 mm: pereopod 5, pereopod 6, pereopod 7, telson, uropod 1, uropod 2, uropod 3, urosome. All scale bars are 0.1 mm.