Metopa insolita, Tandberg & Vader, 2023

Tandberg, Anne Helene S. & Vader, Wim, 2023, A New Stenothoid (Crustacea: Amphipoda: Stenothoidae) from a Shallow Water Hydroid Polyp in British Columbia, Canada, Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 559-565 : 560

Metopa insolita sp. nov.

urn:lsid:zoobank.org:act:A1E4BDF9-2D08-4EC7-B995-16B60772C327

Figs 1B , 2–5

Holotype: ZMBN104469 , male, 3 mm (four permanent slides), Kuldekduma Point , Pearse Island, British Columbia, Canada, 50°35.299'N 126°50.046'W, depth 18 m, from Zyzzyzus rubusidaeus on rock among barnacles and sponges, coll. Neil McDaniel, 30 March 2012 . Paratype: ZMBN, male, 3 mm (ethanol sample), same locality and collection information as for holotype .

Description. Antenna 1 subequal in length to antenna 2, both almost half body length. Antenna 1 peduncle article 1 slightly longer than article 2, article 3 short; flagellum with 17 articles, no accessory flagellum. Antenna 2 article 4 subequal to article 5; flagellum slightly longer than peduncle article 5, with 12 articles.

Head short, cephalic lobe rounded. Eyes ⅓ of head length, round, well defined.

Mandible without molar; incisor and lacinia mobilis serrate; raker setae narrow; palp 3-articulate, article 2 long, article 3 very short with 2 long apical setae.

Maxilla 1 inner plate rounded with 1 simple seta; outer plate flat at distal margin with 1 strong smooth seta and 3 cuspidate setae; palp 1-articulate, smooth with 2 rows with total of 10 simple setae.

Maxilla 2 outer plate in riding position; inner plate with 3 and outer plate with 14 simple setae.

Maxilliped slender; inner plates separate; outer plates reduced; palp 4-articulate with long, simple setae along inner margin and very few shorter and thin setae at distal outer margins of articles 2 and 3; article 4 with short simple setae along inner margin.

Pereon smooth.

Gnathopod 1 simple; coxa short with convex distal margin; basis long, narrow, with long setae on anterior margin; ischium short; merus suboval, distally free, posterior margin with short posterior and longer distal setae; carpus elongate, long simple setae along posterior margin, 3 simple setae along distal margin and 3 long simple setae medially; propodus subequal to carpus in length and slightly narrower, with long simple setae along posterior margin; dactylus narrow and almost straight, inner margin crenulate with short simple setae.

Gnathopod 2 coxa suboval, directed forwards, covering Coxa 1, with few short simple setae along posterior margin; basis straight and narrow with short simple setae along anterior margin; ischium short; merus spoon-shaped, distal margin with short simple setae; carpus triangular, posteriorly enveloped by merus, anterior margin with stridulating ridges; propodus peculiar, roughly rectangular but with large anterior protuberance at base of dactylus, palmar corner rectangular with small tooth, palm crenulate with short simple setae, posterior margin with short setae, anterior margin with stridulating ridges proximally, short setae marginally and longer simple setae distally; dactylus longer than palm, narrow and smooth, bent back over propodus.

Pereopod 3 coxa suboval, short setae at distal margin; remainder of leg slim and simple, meral lobe almost absent; dactylus half propodus length.

Pereopod 4 coxa rounded triangulate, distal margin evenly rounded and slightly thickened; remainder of leg slim but less than that of pereopod 3, with shorter and broader articles; meral lobe ¼ length of carpus.

Pereopod 5 coxa with rounded posterior lobe; basis rectilinear; remainder of leg slim with simple setae along anterior margin; meral lobe less than ¼ of carpus; dactylus slightly longer than half propodus.

Pereopod 6 coxa small with subacute posterior lobe; basis twice as long as broad, subrectangular, with posterior margin slightly concave, small posterodistal crenulated lobe; merus broadened, lobe ⅓ of carpus; carpus narrow; dactylus long and narrow, smooth, curved slightly at tip.

Pereopod 7 coxa small; basis broadly rounded with crenulated convex posterior margin; merus broadened, lobe ⅓ of carpus; dactylus long and narrow, smooth, curved slightly at tip.

Pleon smooth. Epimeral plates 1 and 3 posterodistal corner acute. Epimeral plate 2 posterodistal corner rounded.

Urosome smooth. Length of uropod 1> uropod 2> uropod 3. Uropod 1 peduncle twice length of rami. Uropod 2 outer ramus shorter than inner ramus; peduncle twice as long as inner ramus. Uropod 3 uniramous, ramus shorter than peduncle.

Telson flappable, long and narrow with rounded tip, 4 pairs of marginal robust setae.

Live colour. Translucent white with dark brown-red and pink patches transversally orientated on pereon segments. Eyes white with dark red margin.

Etymology. Named insolita (from Latin “insolitus”— unusual) referring to the unusual shape of the gnathopod 2 propodus in the male.

Ecology. Found sitting on the polyp of the large anthoathecate hydroid, Zyzzyzus rubusidaeus Brinckmann-Voss & Calder, 2013 .

Figures

Figure 1. (A) Metopa insolita sp. nov. sitting on polyp of Zyzzyzus rubusidaeus Brinckmann-Voss & Calder, 2013 (Photo: Neil McDaniel); (B) habitus photo of paratype of Metopa insolita sp. nov. (Photo: A. H. S. Tandberg).

Figure 2. Metopa insolita sp. nov., male holotype, ZMBN 104469: (A) habitus; (B) head with antennae; (C) maxilla 1; (D) mandible; (E) maxilla 2. Scale:A = 1 mm; B–E = 0.1 mm.

Figure 3. Metopa insolita sp. nov., male holotype, ZMBN 104469: (A) gnathopod 1; (B) gnathopod 2. Scale 0.1 mm.

Figure 4. Metopa insolita sp. nov., male holotype, ZMBN 104469: (A) pereopod 3; (B) pereopod 4. Scale 0.1 mm.

Figure 5. Metopa insolita sp. nov., male holotype, ZMBN 104469: (A) pereopod 5; (B) pereopod 6; (C) pereopod 7; (D) epimeral plates 2–3; (E) telson. Scale 0.1 mm.