Mimoscina galbraithae, 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 : 63-68

Mimoscina galbraithae sp. nov.

( Figs. 33–35)

Material examined. Holotype. Female , 5.0 mm ( ZMUC CRU-20429), immature judging by the under-developed oostegites; tropical South Pacific, north-east of Samoa (07°46’S 167°10’W), Dana stn. 3585 IX, 3000 mw, 31 October 1928.

Allotype. Male , 4.7 mm ( ZMUC CRU-20430), immature judging by under-developed genital papillae; southwest Pacific, east of Cook Strait, New Zealand (41°47’S 176°55’E), Dana stn. 3640 VII, 2500 mw, 7 January 1929.

Paratypes. N.E. Atlantic: Two females, 3.3 & 3.9 mm ( ZMUC CRU-20431); north of Madeira (33°26’N 16°59’W), Dana stn. 1142 IX, 2000 mw, 15 October 1921 . N.E. Pacific: Female, about 4.5 mm ( ZMUC CRU- 20432); north-east of Galapagos Islands (02°52’N 87°38’W), Dana stn. 3556 II, 2000 mw, 14 September 1928 . Female, 5.0 mm ( SAMA C6883 ); off Queen Charlotte Island , B.C., Canada (51°59.99’N 135°20.05’W), ex. M. Galbraith, 1500– 1000 m, 30 September 2001 . Male, about 8.2 mm ( SAMA C6884 ); south of Gulf of Alaska (50°12.23’N 144°48.11’W), ex. M. Galbraith, 1000–0 m, 11 June 2005 . S.E. Pacific: Female, about 8.3 mm ( ZMUC CRU-20433); south-east of Galapagos Islands (04°20’S 116°46’W), Dana stn. 3561 IV, 2000 mw, 24 September 1928 . S.W. Pacific: Male, about 6.0 mm ( ZMUC CRU-20434); same data as holotype. Male , 3.8 mm ( ZMUC CRU-20435); north of Samoa (11°00’S 172°37’W), Dana stn. 3587 VI, 1000 mw, 2 November 1928 . Female, urosome missing ( ZMUC CRU-20436); same data as allotype but stn. 3640 VIII, 2000 mw. Three females, 3.2, 3.4 & 5.0 mm ( ZMUC CRU-20437); east of New Zealand (46°43’S 170°08.5’E), Dana stn. 3642 III, 2000 mw, 9 January 1929 . Female, 4.3 mm; male, 3.7 mm ( ZMUC CRU-20438); Tasman Sea (33°26’S 157°02’E), Dana stn. 3656 IV, 2000 mw, 29 January 1929 .

Other material. N.E. Pacific: Female, 3.4 mm & three females, about 4.5 mm ( ZMUC CRU-20439 & CRU- 20440); Gulf of Panama (06°48’N 80°33’W), Dana stns. 1208 V & XVII, 3000 & 1600 mw respectively, 16 June 1922 .

Description of holotype (fig. 33). Female, 5.0 mm; immature judging by the under-developed oostegites.

Pereon slightly inflated, due to enlargement of pereonites 1–5. Antennae 1 missing terminal articles. Antennae 2

reduced, slightly longer than peduncle of A1, consisting of five articles in addition to the gland cone; the third and terminal article with a long seta. Gnathopod 1; basis length 1.5x carpus; propodus marginally shorter than carpus, with several moderate setae on both margins; dactyl relatively strong, length about 0.3x propodus. Gnathopod 2 more slender than G1, but of similar length and structure. Pereopods 3 & 4 similar in structure, with P3 marginally longer; basis length 1.7x merus; merus length 0.7x carpus; propodus length almost 0.8x carpus, with very long seta on antero-distal corner; dactyl length almost 0.2x propodus; merus, carpus and propodus with long setae on both margins, those on posterior margin of carpus especially long. Pereopod 5 length 1.2x P4; basis length 1.7x merus; carpus slightly longer than merus; propodus length about 0.7x carpus; dactyl relatively small, curved, fully retractile. Pereopod 6 slightly longer than P5; basis length about 1.5x merus; carpus length 0.7x merus; propodus length slightly more than 0.7x carpus; dactyl as for P5. Pereopod 7 slightly shorter than P6; basis length twice merus; carpus length 1.6x merus, moderately swollen medially; propodus length and width about half of carpus, or slightly less; dactyl as for P5. Uropoda with relatively slender peduncles and rami; all with inner ramus distinctly longer than outer and slightly longer than peduncle; all rami with slightly serrated margins. Uropod 1; inner ramus length about 1.2x outer, and 1.4x peduncle; outer margin of peduncle distinctly convex, armed with numerous, short, fine setae; proximal part of outer margin of outer ramus also armed with short setae. Uropod 2; inner ramus length about 1.4x outer, slightly longer than peduncle; few fine setae distally on outer margin of peduncle, and proximally on outer ramus. Uropod 3; inner ramus slightly longer than outer, about 1.5x peduncle; peduncle width 0.3x length. Telson with very rounded distal margin, length about 0.4x peduncle of U3.

Description of allotype (fig. 34). Male, 4.7 mm; probably immature. Pereon very slender. Antennae 1 almost as long as head and pereon combined; terminal article with truncate dorsal margin, length almost 4x previous two articles combined. Antennae 2 length about 1.4x A1, consisting of eight slender articles in addition to the gland cone, the third being the longest. Gnathopod 1 similar to holotype, but propodus with more numerous, long setae. Gnathopod 2 slightly shorter than G1, otherwise similar to holotype. Pereopod 3; basis length 1.5x merus; carpus length 1.2x merus; propodus length slightly more than 0.7x carpus, with very long seta on antero-distal corner; dactyl length slightly less than 0.2x propodus. Pereopod 4 with only basis and ischium present on both sides. Pereopod 5; left with only basis-merus present; right with propodus and dactyl missing; basis length 1.5x merus; carpus marginally longer than merus. Pereopod 6 similar in structure and relative length to holotype; propodus with very long seta on postero-distal corner. Pereopod 7 length 0.8x P6; basis length twice merus; carpus length 1.4x merus; propodus length about 0.6x carpus, with long seta on postero-distal corner; dactyl as for P6. Uropoda similar, in structure and relative lengths of peduncles and rami, to holotype. Telson length slightly more than 0.3x peduncle of U3.

Colour not known for living specimens.

Variations. The first antennae of very immature specimens of both sexes often have only two articles terminal to the callynophore, with the terminal article being relatively longer than in the holotype (fig. 33). Presumably an additional article is formed from the division of the terminal one in more mature specimens. The second antennae of very immature males are usually shorter than the first, but never as short as in females; at least not amongst the material examined.

In some specimens the pereopods are slightly more slender than for the holotype or allotype. The pereopods all seem to have a very long seta on the distal corner of the propodus next to the dactyl, although this is not evident for all pereopods in any one specimen, presumably because the setae easily become detached during the collecting process. Similarly, the setae on the peduncle of uropod 3 appear very worn in some specimens. For pereopod 6 the length ratio merus/carpus is about 1.3–1.4, rarely more, except for one male specimen from the north-east Pacific ( SAMA C6884 ), where it is nearly 1.9. In M. gracilipes it is about 2.5. In the holotype, the merus of pereopod 7 is slightly wider than the basis, and the carpus is even wider; more than twice as wide as the propodus. These articles are not as swollen in all female specimens, especially the juveniles. In some specimens the carpus of pereopod 5 is also slightly swollen as for pereopod 7 .

Etymology. This species is named for Dr Moira Galbraith, Institute of Ocean Sciences, Sidney, B.C., Canada, who, over the years, has kindly sent me many interesting specimens from the north-eastern Pacific region, mostly collected by the LaPerouse and Line P Monitoring Programs.

Remarks. Although twenty specimens of this new species are available for study, very few are in good condition, and thus, less mature specimens were selected as the holotype and allotype. The specimens from Dana stn. 1208 (Gulf of Panama) are in particularly poor condition and have been excluded from the type series.

This species is most similar to M. gracilipes but is readily distinguished by the less slender pereopods, especially pereopods 5–7, and by the relatively short merus and swollen carpus (females) of pereopod 7. Similarly it differs from M. setosa as determined in the key.

All of the material, representing this new species, came from the Pacific Ocean except for two females from the north east Atlantic ( Dana stn. 1142 IX). Prior to examining this material in detail I thought that these specimens may be M. gracilipes , as they were captured near the type locality of that species. However, upon further study, most characters proved to be identical to the holotype of M. galbraithae .

Distribution. In the Pacific it has been recorded from a wide range of localities, from the north-east as far north as 52°N, to the south-east and central parts and the south-west as far south as 46°43’S, as detailed above. In the Atlantic it has only been recorded from one locality in the north-east (33°26’N 16°59’W). The specimens from Dana stn. 3656 IV represent a new record for the genus for Australian waters.

Most specimens were captured with 2000 mw, with a few as deep as 3000 mw.