Mimonectes diomedeae ( Woltereck, 1909 )

Zeidler, Wolfgang, 2012, A review of the hyperiidean amphipod families Mimonectidae and Proscinidae (Crustacea: Amphipoda: Hyperiidea: Scinoidea) 3533, Zootaxa 3533, pp. 1-74 : 37-40

Mimonectes diomedeae ( Woltereck, 1909)

( Figs. 16–17)

Sphaeromimonectes diomedeae Woltereck, 1909: 150–151 , pl. 3, fig. 8. Mimonectes diomedeae — Stephensen & Pirlot 1931: 531–532. Shoemaker 1945: 221–224 (part). Vinogradov 1957: 208, fig.

12. Vinogradov 1960: 219. Vinogradov 1964: 127. Vinogradov et al. 1982; 113 (key), 121–122, fig. 51. Garcia-Madrigal

2007: 135, 189 (list). Gasca 2009: 86 (table), 92. Mimonectes gaussi & Mimonecteola macronyx [mis-identification]— Mori et al. 2010: 3 (list), 8 (list).

Type material. The unique holotype, described as female, could not be found in the MCZ, USNM or MFN and is considered lost. The type locality is the south-east Pacific, off Peru (11°59’S 83°40’04”W), Albatross stn. 4667, 600–0 m, 18 November 1904. The original description and figure provided by Woltereck (1909) are very inadequate, and the status of this species has been in doubt in the past (see remarks) .

Material examined. N.E. Atlantic: Juv. male & male ( ZMUC); off Sierra Leone (08°26’N 15°11’W), Dana stns. 4003 III & IV, 4000 & 3000 mw respectively, 9 March 1930 . Male ( ZMUC); off Senegal (13°31’N 18°03’W), Dana stn. 4005 IV, 3000 mw, 12 March 1930 . N.W. Atlantic: Male ( ZMUC); Caribbean Sea (17°54’N 64°54’W), Dana stn. 1186 II, 1000 mw, 30 November 1921 . S.E. Atlantic: Female & three males ( ZMUC); off South Africa (30°15’S 13°15’E), Dana stns. 3978 VII & VIII, 4000 & 3000 mw respectively, 13 February 1930 . Male ( ZMUC); off South Africa (23°26’S 03°56’E), Dana stn. 3980 IX, 3000 mw, 17 February 1930 . Male ( ZMUC CRU-20417); north of St. Helena (07°34’S 08°48’W), Dana stn. 3998 X, 2000 mw, 1 March 1930 . Indo-Pacific: Female ( ZMUC); South China Sea (06°55’N 114°02’E), Dana stn. 3688 III, 3000 mw, 8 April 1929 .

Diagnosis. Females: Body length of mature specimens exceeds 18 mm. Pereon of mature specimens moderately inflated, due to enlargement of pereonites 1–5. Antennae 1 as long as head and first 1.5 pereonites combined (medially). Antennae 2 much reduced, consisting of 4–5 small articles. Gnathopod 1; basis slightly shorter than remaining articles combined; carpus and propodus of similar length; propodus oval-shaped, armed with long, fine setae on both margins (more dense on anterior margin), antero-distal corner produced into petaloid process over-lapping dactyl, postero-distal corner similarly produced but much shorter; dactyl long and slender, length almost 0.3x propodus. Gnathopod 2 slightly longer than G1; basis slightly shorter than remaining articles combined; carpus slightly shorter than propodus; propodus with fine setae on distal margin, both distal corners produced similar to G1; dactyl as for G1, length about 0.2x propodus. Pereopods 3 & 4 similar in structure and length; merus relatively short, length about 1.5x ischium with antero-distal corner slightly produced forward; carpus similar in length to basis, amygdaloid in shape, mid-width almost 0.3x length; propodus length about 0.6x carpus, relatively narrow, tapering distally; dactyl very short and thin. Pereopod 5 slightly longer than P4; basis length twice merus; carpus length almost 1.7x merus; propodus and dactyl missing from available specimens. Pereopod 6 similar in length to P4; basis length about twice merus; carpus length 1.4x merus; propodus sub-equal in length to carpus, relatively thin, tapering distally; dactyl very short and thin. Pereopod 7 slightly shorter than P6; structure and relative lengths of articles similar to P6. Uropoda with relatively broad peduncles and rami; all with inner ramus slightly longer than outer and slightly shorter than peduncle. Uropoda all with inner ramus length 1.2x outer, and 0.8x peduncle. Uropod 3; peduncle width about 0.6–0.7x length. Telson triangular; length about 0.3x peduncle of U3.

Males: Like females except for the following. Largest male recorded only 14 mm. Pereon slightly arched, oval-shaped from dorsal aspect. Antennae 1 as long as head and first four pereonites combined; peduncular articles and callynophore relatively broader. Antennae 2 reduced in immature specimens, possibly exceeding 0.7x length A 1 in mature specimens (mature specimens not available for study). Pereopods 3 & 4; merus relatively shorter, sub-equal in length to ischium; propodus relatively longer, about 0.8x carpus. Pereopod 6 slightly longer than P5, and longest pereopod; basis length 2.4x merus; carpus length 2.2x merus. Pereopod 7 similar to P 5 in length and relative lengths of articles. Uropoda with marginally more slender rami, with inner ramus similar in length to peduncle.

Colour not known for living specimens.

Remarks. The similarity of this species to M. gaussi has already been discussed under that species. It is likely that this species has been misidentified as M. gaussi in the past, with some authors considering the two species synonymous (e.g. Shoemaker 1945). This is partly because Woltereck’s (1909) original description and figure are very inadequate, and it was not until Vinogradov (1957) provided illustrations of the gnathopods that the species was recognised as distinct from M. gaussi .

Distribution. This seems to be a very rare species despite possible confusion with M. gaussi in the past. Apart from the type, there are only seven literature records of specimens captured. Shoemaker (1945) from the North Atlantic, off Bermuda (as M. gaussi , in part); Vinogradov (1957) from the north-western Pacific (39°58’N 164°55’E), 0–5300 m; Vinogradov (1960 a) from the tropical Pacific, off Hawaii (20°21’N 173°24’W), 0–3500 m; Vinogradov (1964) from the tropical south-western Indian Ocean, east of Madagascar (16°07’S 53°39’E), 0–3850 m; Garcia-Madrigal (2007) from the Gulf of California; Gasca (2008) from the Mexican Pacific and Mori et al. (2010) from Sagami Bay, Japan (mis-identified).

The Dana collected eleven specimens, mainly from the eastern Atlantic , ranging from off South Africa north to Senegal, with one specimen from the Caribbean Sea and one from the South China Sea. The latter is a new record for the region. Specimens were collected from a range of depths with 1000–4000 mw, but mostly with 3000 mw .