Metopa cristata Gurjanova, 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 : 44-49

Metopa cristata Gurjanova, 1955

Metopa cristata Gurjanova 1955: 176 –78, fig 7–8 Metopa cristata Shoemaker 1964: 396 –97, fig 3

Type locality: east coast of Iturup Island, Kurile Islands. Sandy bottom, 207m. ( Gurjanova, 1955) Material examined. Morphological examination: NMNH 96488, (Albatross st. 5037: 20 Oct. 1906, E of N. Honshu Isl, Japan, 42°02’ 40”N, 142°33’ 20”E, 640m (349 fathoms), ovigerous female, 6mm, same material as used in Shoemaker 1964

See figures 1, 2, 3 and 4.

Morphological description. Ovigerous female, 6mm.

Head ( Fig. 1 ): epistome small and rounded, cephalic lobe rounded; eye 1/2 of head length, well defined. Antenna 1 ( Fig. 2 ): long and slender, slightly more than half body length; flagellum 17-articulate, with minute setae on each article; no accessory flagellum observed. Antenna 2 ( Fig. 2 ): slightly longer than A1; peduncle more than 3x flagellum; flagellum ca 10-articulate, each article with one minute seta. Mandible ( Fig. 2 ): mandibular palp 2-articulate, circular in cross-section, apical article very small, long thin simple setae on both articles; incisor and lacinia mobilis both serrate and well developed; no molar. Maxilla 1 ( Fig. 2 ): inner plate with one simple distal seta; outer plate with four cuspidate and one conate distal setae and 10 short and simple setae on inner margin; palp 1-articulate, reaching 1.5x length of outer plate, with three cuspidate setae and one tooth apically, four simple setae facially and a row of very short simple setae on inner margin. Maxilla 2 ( Fig. 2 ): outer plate in normal position to and slightly longer than inner plate; both plates with several simple setae (outer with 14 and inner with six). Labrum ( Fig. 2 ): rounded and smooth. Maxilliped ( Fig. 2 ): long and slim; inner plates separate, with a row of short simple setae along distal edge; outer plate reduced, ischium rectangular; palp 4-articulate with several simple setae at inner edge of articles 1 and 2, article 3 with a thickly set "cushion" of setae at tip, article 4 with a single row of short setae along inner edge.

Pereon: smooth; pereonite 1 slightly shorter than the rest. Gnathopod 1 ( Fig. 3 ): subchelate; coxa subquadrate; basis linear, a few simple setae distally; ischium subquadrate, with one long and one short simple distal seta; merus with posterodistal corner free and covered with a row of short and a series of longer simple setae; carpus subrectangular and inner side with long simple setae; propodus slightly shorter than carpus and slightly less broad, almost transverse palm with rounded palmar corner, a few long simple setae on frontal margin, palm distal margin with a row of short, simple setae; dactylus smooth, slightly longer than palm, curved slightly at tip. Gnathopod 2 ( Fig. 3 ): coxa covering coxa 1, directed forwards; merus covering much of carpus, very few and short setae at venterodistal margin of both; propodus palm almost transverse, weakly oblique, coarsely crenulate with simple setae, small, sharp tooth at palmar corner, posterior margin straight, longer than palm; dactylus as long as palm, slightly curved, smooth. Pereopods 3 and 4 ( Fig. 3 ): simple and slender; coxa 3 subrectangular, coxa 4 triangular, ventral margin rounded, dactyli simple. Pereopod 5 ( Fig. 4 ): basis slender, with a posterodistal rounded "tongue" 3/4 length of ischium; meral lobe 1/3 of carpus, a row of very small conical setae at anterior margin of both carpus and propodus; dactylus simple. Pereopods 6 and 7 ( Fig. 4 ): coxae small; basis posteriorly expanded; meral lobe 1/2 and more than 1/2 carpus, respectively, P6 propodus with very small conical setae, similar to P5, but on anterior and posterior margins, P7 propodus with a few at posterior margin; dactyli simple.

Urosome ( Fig. 1 ): smooth. Epimeral plate 3 ( Fig. 1 ): rounded. Uropod 1 ( Fig. 4 ): longer than uropod 2; biramous; peduncle slightly longer than rami, rami subequal in length; inner ramus with three small setae, outer ramus with one small seta. Uropod 2 ( Fig. 4 ): longer than uropod 3; biramous; peduncle slightly longer than rami, inner ramus longer than outer, inner ramus with five small setae, outer ramus with two. Uropod 3 ( Fig. 4 ): uniramous; ramus with two articles, peduncle slightly longer than ramus; peduncle and ramus each with three small setae, rounded, with two pairs of small marginal robust setae. Telson ( Fig. 4 ): rounded, tongue-like; two pairs of setules.

Male and female very similar ( Shoemaker 1964)

Distribution: only known from the type locality (east coast of Iturup Isl, Kurile Islands - sandy bottom 207 m depth) and this Albatross-station (east of northern Honshu Isl, 640m depth).

Discussion: Shoemaker (1964) mentions a 3-articulate mandibular palp, with article 2 very long and article 3 very small. He also mentions four pairs of setules at telson. He further mentions several pereon segments protruding dorsally to a low carinae, which can vary in “truncateness” - we have clearly examined less truncate specimens.

Figures

FIGURE 1. Metopa cristata Gurjanova, 1955, female, 6 mm, Albatross st. 5037: whole animal. Scale bar is 0.5 mm.

FIGURE 2. Metopa cristata Gurjanova, 1955, female, 6 mm, Albatross st. 5037: antenna 1, antenna 2, labrum, maxilla 1, mandible, maxilla 2, maxilliped. All scale bars are 0.1 mm.

FIGURE 3. Metopa cristata Gurjanova, 1955, female, 6 mm, Albatross st. 5037: gnathopod 1, gnathopod 2, pereopod 3, pereopod 4. All scale bars are 0.1 mm.

FIGURE 4. Metopa cristata Gurjanova, 1955, female, 6 mm, Albatross st. 5037: pereopod 5, pereopod 6, pereopod 7, telson, urosome. All scale bars are 0.1 mm.