Mimonectes neosphaericus, Zeidler, 2012

Zeidler, Wolfgang, 2012, A review of the hyperiidean amphipod families Mimonectidae and Proscinidae (Crustacea: Amphipoda: Hyperiidea: Scinoidea) 3533, Zootaxa 3533, pp. 1-74 : 49-53

Mimonectes neosphaericus sp. nov.

( Figs. 24–26)

Material examined. Holotype. Female , 9.7 mm ( SAMA C7061 , ex. JAMSTEC). Sagami Bay, Japan (34°50’N 139°36’E), R/ V Kaiyo stn. IO60320A-4 (cruise KY 06–03), 600–700 m, col. D.J. Lindsay, 20 March 2006.

Allotype. Male , 4.5 mm ( ZMUC CRU-20427). South-eastern tropical Pacific, off Panama (00°18’S 99°07’W), Dana stn. 3558 II, 3000 mw, 18 September 1928.

Paratype. Female, 5.5 mm ( ZMUC CRU-20426). South-west Pacific, Tasman Sea (33°26’S 157°02’E), Dana stn. 3656 IV, 2000 mw, 29 January 1929 .

Other material examined. Juvenile male, in poor condition ( SAMA C6882 ). North-east Pacific, south-west of Vancouver Island (48°0.77’N 126°17.42’W), ex M. Galbraith, stn. LB 16 (cruise 10S0614), 1000– 600 m, 18 September 2006 .

Description of holotype (fig. 24). Female, 9.7 mm, mature judging by the well-developed oostegites. Pereon marginally inflated. Antennae 1 (terminal articles missing) as long as head and first 2.5 pereonites combined (medially). Antennae 2 reduced to small knob. Gnathopod 1; basis length about twice carpus, slightly longer than propodus; carpus with few long setae on distal corners; propodus with two pairs of relatively strong setae on palm, near posterior margin; dactyl relatively strong, pressed against palm of propodus, between row of strong setae, length marginally more than 0.4x propodus. Gnathopod 2 similar to G 1 in structure but slightly longer; basis length twice carpus, 1.2x propodus; carpus with few long setae on distal corners; propodus like G1 but with two additional strong setae medially, on posterior margin, and with slight postero-distal excavation; dactyl relatively strong, pressed against palm, length almost 0.4x propodus. Pereopod 3 the longest, marginally longer than P4; basis length about twice merus, slightly longer than carpus; merus with antero-distal corner slightly produced; propodus length almost 0.9x carpus; dactyl relatively strong, length marginally less than 0.2x propodus. Pereopod 4; basis length about 1.8x merus, and 1.3x carpus; merus with antero-distal corner slightly produced; propodus slightly shorter than carpus; dactyl like that of P3. Pereopod 5 marginally longer than P6, slightly shorter than P4, both similar in relative lengths of articles; basis length about twice merus; carpus marginally longer than merus; propodus length about 0.8x carpus; dactyl a strong, short, curved nail. Pereopod 7 slightly shorter than P6; basis length about 4x merus; merus slightly inflated relative to basis, with slight postero-distal bulge; carpus slightly inflated relative to basis or propodus, length 2.7x merus; propodus length about half carpus; dactyl as for P6. Uropoda with relatively slender peduncles and rami; all with inner ramus distinctly longer than outer and peduncle, especially U1 & 2. Rami all with slightly serrated margins. Uropod 1; inner ramus length almost twice outer and peduncle. Uropod 2; inner ramus length 1.5x outer, and 1.7x peduncle. Uropod 3; inner ramus length 1.2x outer, about 1.5x peduncle; peduncle width half length. Telson triangular, length 1.2x width, about half peduncle of U3.

Description of allotype (figs. 25–26). Male, 4.5 mm; mature judging by the numerous aesthetascs on A1 and well-developed genital papillae. Cuticle relatively thick, opaque. Pereon relatively broad, widest anteriorly, tapering distally, with pereonite 7 only half as wide as pereonite 1. All pereonites with slight furrow dorsally, becoming less prominent posteriorly, that of pereonites 5–7 barely discernible. Antennae 1 slightly longer than head and pereon combined. Antennae 2 reduced to one tiny article. Gnathopod 1; basis length 1.3–1.4x carpus, slightly longer than propodus; carpus with few long setae on distal corners and two on anterior margin; propodus with several long setae along anterior margin, posterior margin with row of relatively strong, paired setae and slight distal excavation; dactyl relatively strong, able to be pressed against palm of propodus, between row of strong setae, length about 0.4x propodus. Gnathopod 2 similar to G 1 in structure and length; basis length 1.6–1.7x carpus, slightly longer than propodus; carpus with few long setae on distal corners; propodus like G1 but without long setae on anterior margin; dactyl pressed against palm, length 0.3x propodus. Pereopod 3 the longest pereopod, almost 1.2x P4; basis length about 1.5x merus, slightly longer than carpus; merus with antero-distal corner slightly produced; propodus length almost 0.8x carpus; dactyl relatively strong, length about 0.2x propodus. Pereopod 4; basis slightly shorter than carpus, about 1.3x merus; merus with antero-distal corner slightly produced; propodus length slightly more than 0.7x carpus; dactyl like that of P3. Pereopods 5 & 6 similar in length and relative lengths of articles, slightly shorter than P4; basis length 1.6x merus; carpus marginally shorter than merus; propodus slightly shorter than carpus; dactyl a short, curved nail. Pereopod 7 marginally shorter than P6; basis length about 2.4x merus; merus with slight postero-distal bulge; carpus length 1.6x merus; propodus marginally longer than merus; dactyl a strong, short, curved nail. Uropoda with relatively slender peduncles and rami; all with inner ramus distinctly longer than outer and peduncle, especially that of U1 & 2. Rami all with slightly serrated margins. Uropod 1; inner ramus length about twice outer and peduncle. Uropod 2; inner ramus length 1.5x outer, about twice peduncle. Uropod 3; inner ramus length 1.2x outer, about 1.8x peduncle; peduncle width about half length. Telson triangular, slightly longer than wide, about 0.6x length peduncle of U3.

Colour not known for living specimens.

Etymology. Combination of the Greek, neos = new, acknowledging the similarity of this species to M. sphaericus .

Remarks. The general habitus and thick cuticle of the allotype is like the males of the previous two species, but it is readily distinguished from both by the structure of the gnathopods. In addition, it differs from M. colemani in that it lacks the cup-like structure on the head, at the base of the first antennae, the pereonite furrows are much less distinct, and the telson is relatively much longer. The structure of the gnathopods bear some resemblance to M. sphaericus , and one might have considered it a variant of this species. Apart from several other minor characters that separate the two, the main ones are that in M. neosphaericus the postero-distal excavation of the propodus of the second gnathopods is only slight, the merus of pereopod 7 is relatively short, and the pereopods have relatively stronger dactyls. In addition, males are readily distinguished by the habitus and thick cuticle, and the telson is also relatively longer. Females are more difficult to distinguish from M. sphaericus , but the much stronger dactyls of the pereopods seems to be a consistent character. In M. sphaericus the dactyls are semi-colon-shaped and relatively fine, whereas in M. neosphaericus they are a strong, relatively thick, short nail, particularly for pereopod 7.

Distribution. Known only from the Pacific Ocean; in the north-west from Sagami Bay, in the south-west, from the Tasman Sea, in the south-east, off Panama and in the north-east, off Vancouver Island, as detailed above.