Mimonectes spandlii Stephensen & Pirlot, 1931

Zeidler, Wolfgang, 2012, A review of the hyperiidean amphipod families Mimonectidae and Proscinidae (Crustacea: Amphipoda: Hyperiidea: Scinoidea) 3533, Zootaxa 3533, pp. 1-74 : 40-42

Mimonectes spandlii Stephensen & Pirlot, 1931

( Figs. 18–19)

Mimonectes spandlii Stephensen & Pirlot, 1931: 532–534 , fig. XII.— Pirlot 1939: 23–24, pl. 1, fig. 5. Shoemaker 1945: 224, fig. 28. Vinogradov et al. 1982: 113 (key), 118–119, fig. 49. Lindsay & Pagès 2010: 34, fig. 1.

Mimonectes steenstrupi [mis-identification]— Pirlot 1929: 46–50, figs. 1–3.

Proscina scinoides [mis-identification]— Vinogradov 1964: 127–129, figs. 11–12.

Type material. This species was described from three specimens, collected by the Armauer Hansen in the northeast Atlantic. A female, 7 mm (mature judging by the oostegites illustrated), from stn. 6, south of Lisbon (38°20’N 09°20’W), 2000 mw, 20–21 May 1922; and two juvenile males, 3 & 5 mm, from stn. 14, off Morocco (34°41’N 09°30’W), 2120 mw, 26 may 1922. The female was designated the holotype and all three specimens are in the collections of the Aquarium-Muséum de l‘Université de Liège, Belgium (RE 11976). The type female is still preserved in alcohol but the two males are now dry .

Material examined. N.E. Atlantic: Female & female ( ZMUC); near Madeira (33°26’N 16°59’W), Dana stns. 1142 VI & VII, 5000 & 4000 mw respectively, 15 October 1921. N.W. Atlantic: Female ( USNM 1149246); “ United States ”, no more data. Female ( ZMUC CRU-9502); “ Groenland Möller 1847”, labelled as “ M. sphaericus ” and listed as M. loveni , specimen 15, by Stephensen & Pirlot (1931). S. Atlantic: Female ( ZMUC CRU-20420); tropical mid-Atlantic (00°31’S 11°02’W), Dana stn. 4000 IX, 3000 mw, 4 March 1930. N.E. Pacific: Male ( ZMUC CRU-20419); Gulf of Panama (06°48’N 80°33’W), Dana stn. 1208 V, 3000 mw, 16 January 1922. N.W. Pacific: male ( SAMA C6881, ex. JAMSTEC); Suruga Bay, Japan (34°43.2’N 138°35.06’E), 1967 m, submersible Shinkai 2000 , Dive 1337, col. D.J. Lindsay, 7 April 2002.

Diagnosis. Females: Body length of mature specimens 8–19 mm. Pereon of mature specimens moderately inflated, due to slightly enlarged pereonites 1–5, becoming grossly inflated when ovigerous. Antennae 1 as long as head and first 1.5 pereonites combined (medially). Antennae 2 reduced to knob (? gland cone). Gnathopod 1; basis slightly shorter than remaining articles combined; carpus slightly shorter than propodus; propodus oval-shaped, armed with row of long, fine setae on anterior margin and with few long setae on posterior margin; dactyl a curved nail, almost half length propodus. Gnathopod 2; length about 1.3x G1; basis as long as remaining articles combined; propodus length about 1.5x carpus, with few fine setae on distal margin; dactyl sharp, curved, length about 0.3x propodus. Pereopods 3 & 4 similar in structure with P4 distinctly longer than P3; merus very short, almost quadrangular, only slightly longer than ischium; carpus moderately broader than propodus, length 0.6–0.7x basis; propodus slightly shorter than carpus; dactyl sharp, curved, length about 0.3x propodus. Pereopods 5–7 stout, with shortened thicker articles. Pereopod 5; length almost 0.7x P4; basis as long as remaining articles combined; merus quadrate, slightly longer than ischium; carpus twice length merus, antero-distal corner with groove for propodus, approaching prehensile structure; propodus length 0.7x carpus; dactyl a curved nail, almost half length propodus. Pereopod 6; length about 0.8x P5; articles similar in structure and relative lengths to P5 except basis is relatively shorter accounting for most of the difference in length. Pereopod 7 slightly shorter and more slender than P6; articles similar in structure and relative lengths to P6 except propodus only slightly shorter than carpus. Uropoda with relatively slender peduncles and rami. Uropod 1; rami sub-equal in length, about 0.7x length peduncle. Uropod 2; inner ramus slightly longer than outer, slightly shorter than peduncle. Uropod 3; rami and peduncle sub-equal in length; peduncle width about half length. Telson triangular; length about half peduncle of U3.

Males: Like females except for the following. Mature specimens not known, largest specimen 6.6 mm (recorded here). Pereon slightly arched, oval-shaped from dorsal aspect. Antennae 1 as long as head and first two pereonites combined; peduncular articles and callynophore relatively broader. Antennae 2 reduced in immature specimens. Pereopods 3 & 4; carpus relatively broader and slightly shorter than propodus; dactyl relatively long, slightly more than half propodus for P3, and slightly less for P4. Pereopods 5–7 all with carpus relatively longer compared to basis, and propodus relatively longer, only slightly shorter than carpus (P5 & 6), or equal to it (P7); dactyl length about half propodus. Uropod 1; inner ramus slightly longer than outer, almost as long as peduncle. Uropod 2; inner ramus slightly longer than peduncle. Uropod 3; inner ramus marginally longer than outer, about 1.5x peduncle.

Colour not known for living specimens.

Remarks. This species is distinguished from all its congeners by the relatively short merus of pereopods 3–7, which is only slightly longer than the ischium, and the relatively strong, curved dactyls of the gnathopods and pereopods. Mimonectes gaussi and M. diomedeae also have pereopods 3 & 4 with a relatively short merus, but that of pereopods 5–7 is relatively much longer, the propodus is relatively long and narrow, and the dactyls are very short and thin. In M. spandlii the articles of pereopods 5–7 are relatively shorter and broader, and the propodus is not narrowed, and the propodus of the gnathopods lacks the distal projections characteristic of M. gaussi and M. diomedeae .

One, poorly preserved, specimen in the ZMUC (CRU-9502), labelled “ Groenland Möller 1847” and identified as “ M. sphaericus ” (? by Bovallius) is most likely this species, judging by the relatively short merus and the relatively strong dactyls of the pereopods. The structure of the gnathopods also precludes this specimen from being identified with M. sphaericus .

From the limited records, this seems to be a relatively small species with females reaching sexual maturity at about 8–19 mm. The female specimen illustrated here (fig. 18), measuring only 8.2 mm, seems to be mature judging by the well-developed oostegites.

An immature male (?) specimen (6.6 mm) from Suruga Bay, Japan (SAMA C6881), captured by submersible, was found in association with the hydromedusan Voragonema tatsunoko (see Lindsay & Pagès 2010).

Distribution. This seems to be a very rare species. Apart from the types, there are only four literature records of specimens captured, including the probable mis-identification of Vinogradov (1964), amounting to a total of only twelve specimens, eight of them juveniles. Pirlot (1939) recorded three juveniles from the north-eastern Atlantic, near the Azores and south of Portugal, from a depth of 0–3000 m; Shoemaker (1945) recorded three females from the north-western Atlantic, off Bermuda; Vinogradov (1964) recorded two juveniles from the tropical Indian Ocean, near the Seychelles, in depths of 2120–3131 m & 1940–3315 m and Lindsay and Pagès (2010) record a juvenile male from Suruga Bay, Japan, collected by submersible from 1969 m. The Dana collected three specimens from the Atlantic, with 3000–5000 mw, and one specimen from the Gulf of Panama with 3000 mw.