Mimonectes colemani, 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 : 46-49

Mimonectes colemani sp. nov.

( Figs. 22–23)

Material examined. Holotype. Female , 8.3 mm ( ZMUC CRU-20424); tropical eastern Atlantic, west of Gulf of Guinea (00°31’S 11°02’W), Dana stn. 4000 VII, 5000 mw, 4 March 1930.

Allotype. Male, 6.8 mm ( ZMUC CRU-20425); as above but stn. 4000 VIII, 4000 mw.

Description of holotype (fig. 22). Female, 8.3 mm; immature judging by the under-developed oostegites. Pereon moderately inflated, due to enlargement of pereonites 1–5. Antennae 1 about as long as head and first pereonite combined (medially). Antennae 2 much reduced, consisting of six short articles in addition to the gland cone. Gnathopod 1; basis almost as long as remaining articles combined; propodus sub-equal in length to carpus with several setae on both margins for distal two-thirds; dactyl relatively strong, length almost half propodus. Gnathopod 2 slightly longer and more slender than G1, otherwise similar to G 1 in structure and relative lengths of articles. Pereopods 3 & 4 similar in structure, with P3 marginally longer mainly due to the relatively longer basis; basis length 2.2x merus for P3, 1.8x merus for P4; merus length almost 0.8x carpus; propodus length 0.8x carpus for P3, not quite 0.7x carpus for P4; dactyl strong, curved nail, length slightly more than 0.2x propodus. Pereopod 5 slightly shorter than P4; basis length almost twice merus; carpus a little shorter than merus; propodus length about 0.6x carpus; dactyl a strong, short, curved nail. Pereopod 6 slightly shorter than P5; basis length about twice merus; carpus slightly longer than merus; propodus length 0.6x carpus; dactyl as for P5. Pereopod 7 slightly shorter than P6, with slightly thicker articles; merus relatively short, only slightly longer than 0.3x basis; carpus length about twice merus; propodus length about 0.7x carpus; dactyl as for P5. Uropoda slightly damaged, with relatively slender peduncles and rami; all with inner ramus distinctly longer than outer and slightly longer than peduncle. Uropod 1; inner ramus length 1.2x outer. Uropoda 2 & 3 damaged; peduncle width of uropod 3 about half length. Telson triangular; length about half peduncle of U3.

Description of allotype (fig. 23). Male, 6.8 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 tapering distally, with pereonite 7 only half as wide as pereonite 1. All pereonites with medial furrow, that of pereonite one the deepest, becoming less prominent and more dorsally orientated towards pereonite 7. Head with lateral cup-like structure over-lapping base of A1. Antennae 1 almost as long as head and pereon combined. Antennae 2 reduced to one tiny article. Gnathopod 1 similar to female holotype, but articles more elongate; basis length about 1.2x carpus; propodus length 0.8x carpus, with numerous long setae on anterior margin and several stronger setae on posterior margin; dactyl relatively strong, length about one-third propodus. Gnathopod 2 similar to female holotype but slightly shorter than G1; basis length about 1.5x carpus; propodus sub-equal in length to carpus; dactyl more slender than for G1 but of similar length. Pereopod 3 is clearly the longest pereopod, almost 1.2x P4; basis length 1.5x merus, equal to carpus; propodus length about 0.8x carpus; dactyl relatively slender, length almost 0.3x propodus. Pereopod 4; basis slightly longer than carpus, about 1.4x merus; propodus slightly shorter than carpus; dactyl as for P3. Pereopod 5 slightly longer than P4; basis length almost 1.7x merus; carpus and merus similar in length; propodus length 0.7x carpus; dactyl a short, strong nail. Pereopod 6 slightly shorter than P5 but all articles of similar relative lengths. Pereopod 7 similar in length to P6; basis length almost 2.5x merus; carpus length 1.5x merus; propodus length about 0.6x carpus; dactyl like that of P5 & 6. Uropoda with relatively slender peduncles and rami; all with inner ramus distinctly longer than peduncle and outer ramus; especially U1 & 2. Uropod 1; inner ramus length about twice outer, and 1.7x peduncle. Uropod 2; inner ramus length 1.6x outer, about 1.3x peduncle. Uropod 3; inner ramus length about 1.3x outer, slightly longer than peduncle; peduncle width slightly more than one-third length. Telson triangular, length slightly more than 0.3x peduncle of U3.

Colour not known for living specimens.

Etymology. This species is named for Dr C.O. Coleman, Curator of Crustacea, Museum für Naturkunde, Berlin, in recognition for his considerable assistance, in many ways, to facilitate my studies of hyperiidean amphipods.

Remarks. This species is most similar to M. loveni and M. spandlii in having simple gnathopods, without projections adjacent to the dactyls, or postero-distal excavations on the propodus (e.g. M. sphaericus ). It is readily distinguished from M. loveni by several characters, but mainly by the structure of the gnathopods which are much less setose and more slender, and by the strong dactyls of the gnathopods and pereopods. It is easily distinguished from M. spandlii by the relatively longer merus of the pereopods. In addition, males are distinguished by the general habitus and the thick, opaque cuticle. In this regard, males resemble M. alexanderi , but M. colemani is distinguished by the gnathopods (propodus lacking postero-distal projection), the pereonite furrows, and the cuplike structure at the base of the first antennae.

This may also be a relatively small species because, although the female (8.3 mm) is immature, the male (6.8 mm) seems to be mature, based on the numerous aesthetascs on the first antennae and the well-developed genital papillae. However, it is interesting to note that the second antennae of the male are much reduced, unlike most other species of Mimonectes . Thus, it is possible that, despite some secondary sexual characteristics being welldeveloped, the allotype may be immature.

Distribution. Known only from the type locality, as detailed above.