Mimonectes alexanderi, 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 : 43-45

Mimonectes alexanderi sp. nov.

( Figs. 20–21)

Material examined. Holotype. Female , 7.3 mm ( ZMUC CRU-20421); north-east Atlantic, Bay of Biscay (46°28’N 08°01’W), Dana stn. 4158 XXII, 5500 mw, 18 June 1930. Mouthparts mounted on microscope slide; remainder in spirit.

Allotype. Male, 5.3 mm ( ZMUC CRU-20422); Indo-Pacific, Banda Sea (05°52’S 131°14’E), Dana stn. 3676 IX, 3000 mw, 23 March 1929.

Paratypes. Female , 5.6 mm, with well-developed oostegites ( ZMUC CRU-20423); central eastern Pacific, Gulf of Panama (06°48’N 80°33’W), Dana stn. 1208 VI, 2500 mw, 16 January 1922 . Male , 4.3 mm, mature ( SAMA C7015 , ex. JAMSTEC); Sagami Bay, Japan (34°50’N 139°36’E), R/ V Kaiyo stn. IO60320A-3 (cruise KY 06–03), 700–800 m, col. D.J. Lindsay, 20 March 2006 .

Description of holotype ( Fig. 20). Female, 7.3 mm; mature judging by the well-developed oostegites. Pereon moderately inflated, due to enlargement of pereonites 1–5. Antennae 1 (tip missing) about as long as head and first three pereonites combined (medially). Antennae 2 much reduced, consisting of four small articles. Gnathopod 1; basis almost as long as remaining articles combined; carpus broader and slightly longer than propodus, with broad distal margin; propodus with postero-distal corner produced into sharp process, as long as, and over-lapping dactyl; dactyl slender, length about 0.2x propodus. Gnathopod 2 slightly longer and more slender than G1; basis almost as long as remaining articles combined; carpus length about two-thirds propodus and slightly broader; propodus tapering distally with postero-distal projection as for G1; dactyl length slightly less than 0.2x propodus. Pereopods 3 & 4 similar in structure, with P3 marginally longer; merus relatively short, length about one-third basis, slightly less than twice ischium, or about half propodus, with antero-distal corner slightly produced forward; carpus sub-equal in length to propodus; dactyl slightly curved, length about 0.3x propodus. Pereopod 5 relatively short, about 0.8x P4; basis length slightly less than twice carpus; merus slightly longer than carpus; propodus length 1.4x carpus; dactyl a short curved nail. Pereopod 6 slightly shorter than P5, with articles of similar proportions, except for the propodus, which is equal in length to the carpus. Pereopod 7 slightly shorter than P6 and with slightly thicker articles; basis slightly longer than that of P6, about 2.5x carpus; merus length 0.7x carpus; propodus slightly shorter than carpus; dactyl a robust, curved nail, almost half length propodus. Uropoda with relatively slender peduncles and rami; all with inner ramus distinctly longer than outer and marginally longer than peduncle. Uropod 1; inner ramus length about 1.6x outer. Uropod 2; inner ramus length about 1.5x outer. Uropod 3; inner ramus length about 1.3x outer; peduncle width 0.3x length. Telson triangular; length about 0.3x peduncle of U3.

Description of allotype ( Fig. 21). Male, 5.3 mm; mature judging by the numerous aesthetascs on A1 and the well-developed genital papillae. Cuticle relatively thick, opaque. Pereon relatively broad, widest anteriorly, gradually narrowing distally, with width of pereonite 7 about 0.6x that of pereonite 1. Pereonites 6 & 7 and pleonites with slight dorsal keel. Antennae 1 slightly longer than head and pereon combined. Antennae 2 only slightly longer than peduncle of A1, consisting of only three articles with a long terminal seta. Gnathopod 1 similar to female holotype but with more slender articles; propodus slightly longer than carpus, anterior margin armed with numerous long setae; dactyl length slightly more than 0.3x propodus. Gnathopod 2 similar to female holotype but with basis relatively shorter. Pereopods 3 & 4 similar in structure, with P3 marginally longer; all articles relatively broader than in female; merus with antero-distal bulge, length about half basis or about 1.5x ischium, or about 0.7x propodus; propodus marginally longer than carpus; dactyl slightly curved, length slightly more than 0.3x propodus. Pereopods 5–7 similar to female holotype. Uropoda similar to female holotype but slightly less slender; peduncle of U3 relatively shorter, and telson less pointed, length about 0.4x peduncle of U3.

Colour not known for living specimens.

Etymology. This species is named to honour Dr C.G. Alexander (recently deceased) formerly Senior Lecturer, James Cook University of North Queensland, Townsville, who first introduced me to the fascinating realm of hyperiidean amphipods.

Remarks. This species is readily distinguished from all its congeners by the postero-distal projection of the propodus of the gnathopods. In this respect, it also resembles M. gaussi and M. diomedeae , which have similar projections, but on both sides of the dactyl, with the anterior one being the more prominent. It also resembles M. spandlii in having pereopods 3 & 4 with a relatively short merus, and pereopods 3–7 with strong dactyls, but differs mainly in the structure of the gnathopods and the relatively longer merus of pereopods 5–7. The male is unlike any of the previous species, but like the following two, in having a thick, opaque cuticle, an anteriorly broadened pereon, a broad head (viewed dorsally), and much reduced second antennae. The structure of pereopod 7, especially the almost falcate dactyl, is very similar to Pseudomimonectes robustus , and initially I thought that this species might also belong to this genus, but the mandible is without a palp, and the lacinia mobilis is narrower than the incisor (fig. 20), characters consistent with Mimonectes .

This seems to be a relatively small species. All four specimens examined seem to be mature, judging by the well-developed oostegites of the females (7.3, 5.6 mm), and the well-developed aesthetascs of the first antennae, and well-developed genital papillae of the males (4.3, 5.3 mm).

Distribution. Known only from the Bay of Biscay, Banda Sea, Sagami Bay, Japan and the Gulf of Panama, as detailed above.