New and poorly described stenothoids (Crustacea, Amphipoda) from the Pacific Ocean. Author Krapp-Schickel, T. text Memoirs of Museum Victoria 2009 2009-12-31 66 1 95 116 https://museumsvictoria.com.au/collections-research/journals/memoirs-of-museum-victoria/volume-66-issue-1-2009/pages-95-116/ journal article 10.24199/j.mmv.2009.66.12 1447-2554 12211798 Metopa exigua n.sp. Figs. 10–11 Holotype : one male 2mm . Off Korea , 38°15'N , 128°45'E , 200m depth , coll. Schönau IV/1897 . Slide ZMUC CRU-20191 . Additional material: 2 females ov. 1.8mm same locality. Slides ZMUC CRU-20192 . Type locality: off Korea . Etymology: from Latin „exiguus“ meaning poor, weak, tiny, minute. Description. Based on male 2mm , female 1.8mm Body. Smooth. Head. Eyes rounded. Antenna 1 peduncle article 1 length about three times the width in female, in male slimmer; article 2 in female shorter, in male much longer than article 1 ; flagellum 13–14 articles, accessory flagellum absent. A 2 clearly shorter than A1, peduncle article 4 the longest, flagellum shorter than peduncle, with 6–10 articles. Mouthparts . Mandible palp with one quadrangular basal article and a long, thickened second one which is more than 3x longer than article 1, and a very short and small third article carrying 1 long distal seta. Maxilla 1 palp with 1 article; Maxilla 2 plates in ordinary tandem position; Maxilliped IP not fused; OP visible as acute tooth-shaped prolongation; dactylus long, shorter than propodus. Peraeon. Coxae . Cx2 oval without tooth; Cx3 tongue-shaped to rectangular, Cx4 not excavated, anterior margin straight, posterior one rounded. Gnathopods . Gn1, 2 propodi extremely different in shape and size. Gnathopod 1 propodus rectangular and narrow, palm not defined; carpus clearly longer and wider than propodus, proximally narrower than distally; merus without free distal end; all articles beset with groups of short setae. Gnathopod 2 male propodus hind margin longer than length of palm which has one deep rounded excavation near thumb-shaped palmar corner and many small serrations next to dactylus insertion; these incisions show single setae; dactylus somewhat shorter than length of palm. Gn2 carpus longer than wide, triangular, merus not lobate. Peraeopods. P3 basis elongate and slender; all other articles elongate and weak, dactylus longer than half propodus, weak and smooth. P4 all articles much more robust, with dense setation; merus somewhat curved; dactylus longer than half propodus. P5–P7 merus wider than carpus and only shortly lengthened posterodistally; basis P6, 7 widened with rounded posterodistal lobe; all peraeopods with short setation. Pleon. Uropods. U1 peduncle longer than subequal rami, with short robust setae on peduncle and rami; U2 peduncle also beset with small robust setae, longer than longer ramus, rami very unequal; U3 peduncle shorter to subequal ramus, article 1 of ramus shorter or subequal to the spineshaped robust article 2. Telson . Triangular, distally pointed, with few marginal robust setae. Habitat. 200m depth. Distribution . Off Korea , Pacific Ocean. Remarks. At first sight this species looks similar to Metopa wiesei Gurjanova, 1933 , as the second male gnathopod is nearly identical. For a better comparison I provide here a detailed translation of the original description of the latter species: „ Metopa wiesei Gurjanova 1933: 123 ; 1951 ; 421 fig. 260 Type locality: Jugorsky Shar, 69° 46'N , 60°35'O , 20m depth. Translation of original description in Gurjanova 1933 : Length 3.5mm. Eyes large, roundish. Antennae long; A1 article 1 as long as 2+3 together; flagellum 13 articles. A2 somewhat longer than A1, peduncle article 3> article 2; flagellum short, 7 articles. Mxp inner plate not fused; last articles of palp with short stiff setae on inner margin and basis. Mx1 palp with 1 article, Md palp with 2 articles. Cx 4 evenly rounded, very large. Peraeopods robust. P6,7 basis short, broad, merus broadened and lengthened. Gn1 simple, dactylus on inner margin with short setae. Gn 2 in male strongly developed with a long acute tooth on palmar corner; palm with 5 rounded humps which are stronger versus outer margin. Ep3 with acutely lengthened posterodistal corner. T oval, with acute tip and 3 pairs of thick dorsal robust setae. U3 peduncle with 3 thick robust setae, ramus articles subequal, but shorter than peduncle. Stands near to Metopa clypeata , but Ep3, eyes, antennae, both gnathopods and telson shape are different.“ This description, without any illustrations in Gurjanova 1933 , but with some sketchy ones in Gurjanova 1951 , makes clear that mainly the antennae (A1 article1 as long as article 2+3 together)and peraeopods (merus broadened and lengthened) are very different from the newly coined species. It seems also probable that M. wiesei has a more robust body living in 20m depth, while M. exigua n.sp. has the thin and delicate legs of typical mud inhabitants (it comes from 200m depth). Figure 10: Metopa exigua n.sp. : holotype male 2mm, female 1.8mm, off Korea. Figure 11: Metopa exigua n.sp. : holotype male 2mm, female 1.8mm, off Korea. The new species belongs to a difficult group with often not very clear morphological character-states: Metopa abyssi Pirlot, 1933 ; M. angustimana Gurjanova, 1948 ; M. bruzelii (Goes, 1866) ; M. dawsoni Barnard, 1962 ; M. longicornis Boeck, 1871 ; M. longirama Dunbar, 1942 ; M. palmata Sars, 1895 ; M. quadrangula Reibisch, 1905 ; M. tenuimana Sars, 1895 ; M. wiesei Gurjanova, 1933 . They all share the simple Gn1 with elongate propodus and carpus, which are similarly wide (vs. carpus much wider in the group around the type species M. clypeata ) and should be separated from the other members of Metopa . It should also be checked, if all of them have the inner plates of the maxilliped well separated like the type M. clypeata and unlike many other Metopa members.