Metopa eupraxiae, Krapp-Schickel, 2009

Krapp-Schickel, T., 2009, New and poorly described stenothoids (Crustacea, Amphipoda) from the Pacific Ocean., Memoirs of Museum Victoria 66 (1), pp. 95-116 : 103-107

Metopa eupraxiae n.sp.

Figs. 7–9

Stenothoides carinatus Gurjanova 1953: 230–233 , figs. 13, 14 Stenula carinata (Gurjanova) in: Barnard & Karaman 1991: 69

(change of genus for the illustration of the Md palp without articulation) non Metopa carinata Hansen 1887:311 = Metopella carinata in

Gurjanova 1951: 474, figs. 311

Holotype: Tsugaru Strait = Tsugaru-kaikyo (41° 37'N, 140° 52'E), N-Japan, between Japan Sea and Pacific Ocean, on hydroid Sertularia crassicornis Allman , coll. Suensen 1882, 200m depth; 1 male 4mm (18) slide ZMUC CRU-20187 .

Additional material: same locality, same collector, 1 female slide ZMUC CRU-20188 ; 38 specimen (males, females, juveniles) in alcohol. 2 adult specimens 4mm in alcohol, coll. Suensen 1882 and 1893 ZMUC CRU-20201 & CRU-20202 , 2 slides ZMUC CRU-20189 & CRU-20190 ; 2 specimens in alcohol, probably juveniles. ZMUC CRU-20203 .

Etymology: In honour to Eupraxia Gurjanova.

Description. Based on male, 4 mm

Body. Posterior half carinate.

Head. Eyes rounded. Antenna 1 peduncle robust, article 1 length about three times the width; flagellum 18 articles, accessory flagellum absent. A 2 clearly longer than A1, peduncle robust, flagellum shorter than peduncle, with 14 articles.

Mouthparts. Mandible palp clearly visible with one rectangular basal article and a long second one which is more than 3x longer than article 1, with 3 distal and some marginal long setae; the usual article 3 is missing. Maxilla 1 palp with 1 article; Maxilla 2 plates in ordinary tandem position; Maxilliped IP not fused, about 2/3 length of ischium; OP visible as acute tooth-shaped prolongation; dactylus long, subequal to propodus.

Peraeon. Coxae. Cx2 oval without tooth; Cx3 tongue-shaped, 2.5x longer than wide, Cx4 not excavated, anterior margin straight, posterior margin rounded, about 1.5 x wider than long.

Gnathopods. Gn1, 2 propodi extremely different in shape and size. Gnathopod 1 propodus rectangular, palm oblique, well defined, remaining hind margin longer than palm; carpus clearly longer than propodus, with parallel margins, proximally somewhat narrower than distally; merus incipiently chelate, with free distal end; all articles beset with groups of long setae. Gnathopod 2 length of propodus subequal to longer than Cx2; propodus trapezoidshaped, rectipalmate; anterior margin beset with robust setae; hind margin subequal to length of palm which has one deep excavation near thumb-shaped palmar corner and 5 humps next to dactylus insertion; incisions between these humps have long setae which get lost with age; dactylus same length like palm. Gn2 carpus much shorter than wide, cup-shaped, merus not lobate.

Peraeopods. P3 basis elongate but proximally swollen, with glands inside; anterior margin regularly beset with many short setae; all other articles elongate and weak, dactylus longer than half propodus, weak and smooth; all articles except basis have short setae on posterior margin. P4 all articles much more robust, but without setation; merus anterodistal margin lengthened and rounded; dactylus on inner side strongly serrated like in P5–7. P5–P7 merus about twice as wide as carpus and only about 1.25% lengthened posterodistally, reaching ca the proximal third of carpuslength; basis P6, 7 widened with rounded posterodistal lobe.

Pleon. Uropods. U1 peduncle shorter than subequal rami, with short robust setae on peduncle and rami; U2 peduncle also beset with small robust setae, shorter than longer ramus, rami very unequal (about 3:2); U3 peduncle much shorter than ramus, article 1 of ramus subequal to peduncle and much longer than the claw-shaped robust article 2.

Telson . Not reaching end of peduncle U3, with 3 robust setae on each side.

Habitat. On hydroids, 200m depth.

Distribution. Tsugaru Strait, between the Japan Sea and Pacific Ocean.

Remarks. Gurjanova,1953 described a new species Stenothoides carinatus from the Kuril Islands East of Japan, between the Kamchatka Peninsula and the Japanese Hokkaido. Two years later she published another new species from a similar locality, Metopa kobjakovae . These two species differ mainly in the presence/absence of a third article in the mandibular palp, the length of U3 ramus article 1 and the spination of the telson with presence/absence of robust setae also on the upper surface.

The present material is very close to Stenothoides carinatus Gurjanova 1953 , which was later given to Stenula by Barnard & Karaman, 1991 for the Md palp drawn without any articulation. But in the present specimens there is clearly visible a proximal first article on the Md palp, and furthermore the gnathopods are indicating a close relationship to Metopa , not to Stenula .

As the name Metopa carinata is already occupied, although in synonymy with other taxa, there had to be created a new name for this species. It matches well the drawings of Gurjanova, 1953 for Stenothoides carinatus except:

• Gn1 propodus palmar corner a bit wider than 90° (in Gurjanova exactly 90°)

• the shorter merus on P 4–7 in our material,

• the not illustrated serration of the dactyli in P4–7 (clearly present in our material)

• the spination in U3 and T (richer in Gurjanova‘s species).

The differences from our material to Metopa kobjakovae are:

• Md palp with 3 articles

• Gn1 propodus palmar corner a bit wider than 90° (in Gurjanova exactly 90°)

• U3 ramus article longer

• T richly spinose

• nowhere mentioned a carinate body in M. kobjakovae , while the serration on P6, 7 is illustrated.

It could be that all three species are synonymous and show allometric differences, in this case the new species presented here would become junior synynym of Metopa kobjakovae ; but for the time being I cannot check if M. kobjakovae also has a carinate body and if older specimens of the other species become more richly spinose.

Figures

Figure 7: Metopa eupraxiae n.sp.: holotype male 4mm, N Japan.

Figure 8: Metopa eupraxiae n.sp.: holotype male 4mm, N Japan.

Figure 9: Metopa eupraxiae n.sp.: holotype male 4mm, N Japan.