Malvinometopa porcellana (KH Barnard, 1932)

Krapp-Schickel, Traudl, 2011, On the Austral-Antarctic stenothoids Proboloides, Metopoides, Torometopa and Scaphodactylus (Crustacea Amphipoda) Part 2: the genus Proboloides, with description of two new genera and the transfer of two nominal species to Metopoides, ZooKeys 86, pp. 11-45 : 16-19

Malvinometopa porcellana (KH Barnard, 1932) Figs 12

Proboloides porcellanus KH Barnard 1932: 111-112, fig. 61

Torometopa porcellana Barnard and Karaman 1991: 700

Material examined:

Type material BMNH.

Redescription of type material:

Body

smooth. Eyes rounded, large.

Length:

5-9 mm.

Antennae.

A1 less than half of body length, peduncle robust, art 1 length about three times the width; acc. flag. absent, flagellum 6-7 arts. A2 subequal in length to A1, peduncle robust, art 4 <art 5, flagellum about as long as or shorter than peduncle art 5, with 7 arts.

Mouthparts.

Md palp with 3 arts, art 1 and 2 unusually long, art 3 much shorter than 1/3 length of art 2, with many distal setae. Mx 1, 2 unknown; Mxp IP not fused, 2/3 length of ischium; OP vanishing; dactylus long, subequal to propodus.

Coxae.

Cx2 with rounded anterior margin, straight behind, angle rounded without tooth; Cx3 trapezoid-shaped, distally widening, Cx4 not excavated, anterior and posterior margin rounded, about as long as wide.

Gnathopods.

Gn1, 2 propodi similar in shape, different in size. Gn1 dactylus ordinary; propodus with parallel margins, palm not defined, about twice as long as wide; carpus longer than propodus, subtriangular, longer than wide, proximally wider than distally; merus incipiently chelate; all articles densely beset with setae. Gn2 length of propodus more than 2/3 of Cx2; propodus subelliptical, twice the size of propodus Gn1; hind margin subequal to length of palm which has shallow incisions, palmar corner well defined by small tooth-shaped prolongation but no U-shaped incision. Dactylus same length as palm. Gn2 carpus shorter than wide, cup-shaped, merus not lobate.

Peraeopods.

P4 merus anterodistal margin somewhat lengthened. P5 dactylus half length of slim propodus; merus posterodistal margin not reaching half of carpus length, basis rectolinear with short posterodistal lobe. P6 basis hind margin straight, with posterodistal lobe similar to P5, merus posterodistal corner acutely lengthened and somewhat widened, not reaching to half of carpus length. P7 basis proximally widened with lobe, distad narrowing with small posterodistal lobe, hind margin crenulate and excavated; merus lengthened and widened, reaching about half carpus length.

Uropods.

U1 peduncle with many short robust setae, nearly twice as long as subequal rami; U2 peduncle also beset with many small robust setae, longer than longer ramus, rami somewhat unequal; U3 totally unarmed, peduncle longer than ramus, art 1 of ramus longer than art 2.

Telson.

Not reaching end of peduncle U3; less than twice as long as wide; distally tongue-shaped rounded, naked.

Sexual differences.

Small.

Distribution.

Falkland Islands.

Ecology.

From pharynx of a large ascidian.

Remarks.

Malvinometopa porcellanus has extremely shortened A1, 2, no Mxp OP, a stout Gn1 and aberrant P6, 7: is this an adaptation to the life inside the pharynx of ascidians, where they certainly cannot swim but only crawl? All we know is that space there is at a premium.