Mimonectes sphaericus Bovallius, 1885

Zeidler, Wolfgang, 2012, A review of the hyperiidean amphipod families Mimonectidae and Proscinidae (Crustacea: Amphipoda: Hyperiidea: Scinoidea) 3533, Zootaxa 3533, pp. 1-74 : 28-32

Mimonectes sphaericus Bovallius, 1885

( Figs. 12–13)

Mimonectes sphaericus Bovallius, 1885: 11–12 , pl. 2, fig. 12.— Bovallius 1887 a: 15; 1889: 66–69, pl. 6, figs. 1–10. Woltereck 1904a: 622–624. Woltereck 1904b: 629 (key). Stephensen 1923: 6. Schellenberg 1927: 600, fig. 10. Stephensen & Pirlot 1931: 516–519, figs. V & VI. Behning 1939: 354 (table), 356–357, fig. 4. Pirlot 1939: 21–22. Shoemaker 1945: 219, fig. 24. Vinogradov 1956: 201. Vinogradov 1957: 165–166, 179 (table) [English]. Vinogradov 1960: 218. Vinogradov 1962: 13. Vinogradov 1964: 126. Hurley 1969: 33. Vinogradov 1970: 385 (table). Vinogradov et al. 1982: 113 (key), 114–116, figs. 46–47. Barkhatov & Vinogradov 1988: 245 (table). Vinogradov 1992: 325. De Broyer & Jazdzewski 1993: 106. Vinogradov & Semenova 1996: 619. Vinogradov 1999: 1147 (table), 1172, fig. 4.45. Vinogradov et al. 2004: 9, 25 (table). Gasca 2006: 239 (table), fig. 3d. Garcia-Madrigal 2007: 135–136, 189 (list). Zeidler & De Broyer 2009: 15. Mori et al. 2010: 8 (list).

Sphaeromimonectes valdiviae Woltereck, 1904a: 622–625 , fig. 1.— Woltereck 1904b: 629. Woltereck 1906: 868–869, fig. 6.5b. Woltereck 1927: 82–84, figs. 23, 24b, 25b.

Mimonectes valdiviae — Stephensen & Pirlot 1931: 530. Pirlot 1932: 22–23, fig. 14. Pirlot 1939: 23.

Sphaeromimonectes valdiviae pacifica Woltereck, 1909: 148–150 , pl. 1, fig. 4; pl. 2, fig. 6.

Sphaeromimonectes valdiviae forma typica Woltereck, 1909: 148–150, pl. 2, fig. 7.

Parascina fowleri [mis-identification]—Reid 1955: 13 (only stn. 139).

Proscina stephenseni [mis-identification]— Vinogradov 1957: 208–209, fig. 13. Gasca et al. 2006: 239 (table), fig. 3e.

Type material. Bovallius (1885) gives the type locality as “The Atlantic: 28°N.L. 21°V.L., near the Canary Islands”, but does not specify the sex or number specimens examined, and illustrates an apparently mature female. Later (1889) he gives a size range of 12–16 mm, indicating that, at that time, he had more than one specimen. The NRS has only one specimen of M. sphaericus dating from Bovallius’s time (No. 1747). It is from the North Atlantic (58°N 28°W), and is partly dissected with a red “X” on the label. It is likely that this specimen was seen by Bovallius (1889) but must be disregarded as type material because it is not from the type locality, and there is no indication on the label that it is type material. Similarly, the ZMUC also has a female specimen from the North Atlantic (46°N 18°W), W. Hygom XI-1856, which was described and illustrated by Stephensen and Pirlot (1931), but is not regarded type material. However, there is one female specimen in the ZMUC (CRU-8175) which is from the type locality, and on the label is written “Vandklar med hójróde punkter Hygom”, referring to the colour, “hyaline with red spots”, as recorded by Bovallius (1885). This is almost certainly type material, but the specimen is in two pieces with the head, gnathopods and some parts of the pereopods missing. Without the gnathopods it is impossible to identify this specimen with M. sphaericus with any degree of certainty, and so it must remain questionable type material.

Type material of synonyms. Sphaeromimonectes valdiviae was presumably described from the material collected by the Valdivia , during the Deutschen Tiefsee-Expedition 1898–99. Woltereck (1904a) does not give any locality data, but later (1904b) mentions that he now has two more specimens from the Deutschen Südpolar- Expedition 1901–03, and subsequently (1906) refers to the smaller Valdivia example. The MFN does not have any specimens from the Valdivia expedition, and so the type of S. valdiviae must be considered lost, but it does have a specimen from the latter expedition labelled “ Type ” ( MFN 21335). This specimen is a mature female, about 21–23 mm in length, with a much inflated pereon, collected by the Gauss from the North Atlantic (33°55’N 16°09’W), 30 July 1901. This specimen, although labelled “ Type ” is considered very questionable type material because it was not collected by the Valdivia , was not mentioned by Woltereck (1904a) until after the original description ( Woltereck 1904b), and the pereon is much more inflated than that illustrated by Woltereck (1904a). However, an examination of this specimen, and an analysis of Woltereck’s descriptions and figures of this species, confirm the currently accepted synonymy with M. sphaericus .

Type material of S. valdiviae pacifica could not be found in the MCZ, USNM or MFN and is considered lost. Woltereck (1909) based this new sub-species on a male specimen from the mid-south-eastern Pacific, near the Galapagos Islands (10°15’22”S 95°40’8”W); Albatross stn. 4709, 600–0 m, 31 December 1904. The differences noted by Woltereck can be attributed to the sexual dimorphism observed in this species, and it is considered a synonym of M. sphaericus , along with S. valdiviae .

Woltereck (1909) proposed the name S. valdiviae forma typica for the typical form of S. valdiviae found in the Atlantic, to distinguish it from S. valdiviae pacifica from the Pacific. As this name was proposed only in a general discussion of the species, it is unlikely that a type was selected, or deemed necessary, and none could be found in the USNM or MFN.

Material examined. Types. Questionable type material of M. loveni and S. valdiviae as detailed above.

Other material examined. N.E. Atlantic: Female ( NHM 1961.8.1.306); north-west of Gulf of Guinea (01°30’N 10°10’W), Atlantide stn. 139, 1750 mw, 2 April 1946 . Male ( ZMUC); south-west of Cape Verde Islands (12°11’N 35°49’W), Dana stn. 1165 III, 600 mw, 9 November 1921 . Male & female ( ZMUC); west of Sierra Leone (08°26’N 15°11’W), Dana stns. 4003 II & VII, 5000 mw, 9 March 1930 . Juv. ( ZMUC); off Senegal (13°31’N 18°03’W), Dana stn. 4005 VI, 1000 mw, 12 March 1930 . Juv. female ( ZMUC); Bay of Biscay (46°28’N 08°01’W), Dana stn. 4158, 2000 mw, 18 June 1930 . S.E. Atlantic: Female & six males ( ZMUC); off South Africa (30°15S 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 VII, 5000 mw, 17 February 1930 . Three males ( ZMUC); near St. Helena (15°41’S 05°50’W), Dana stn. 3996 II, 3000 mw, 25 February 1930 . Juv. ( ZMUC); north of St. Helena (07°34’S 08°48’W), Dana stn. 3997 VII, 5000 mw, 1 March 1930 . Female & two males & two females ( ZMUC); south of Liberia (00°31’S 11°02’W), Dana stns. 4000 III, VII & XI, 300, 5000 & 1000 mw respectively, 4 March 1930 . N.E. Pacific: Male & male ( ZMUC); north of Galapagos Islands (02°52’N 87°38’W), Dana stns. 3556 II & V, 2000 & 600 mw respectively, 14 September 1928 . Male ( ZMUC); Gulf of Panama (06°48’N 80°33’W), Dana stn. 1208 XIV, 3100 mw, 16 January 1922 . Male ( SAMA C6871 ); off Baja California (35°30’N 123°52’W), ROV HyperDolphin dive 842, 1082 m, 7 April 2005 . Juv. ( SAMA C6873 ); off Pismo Beach, California (35°38’N 122°44’W), ROV dive 984–05, 690 m, 13 May 2006 . Female ( SAMA C6872 ); same stn. as above, ROV dive 985–09, 1344 m, 14 May 2006 . Female ( SAMA C6874 ); Monterey Canyon, California (36°68.5’N 122°06.3’W), ROV dive 843, 392 m, 5 May 2003 . Male ( SAMA C6875 ); Endeavour Ridge, ‘ Hot Vent’ (48°10’N 129°45’W), ex. M. Galbraith, 18 July 1991 . N.W. Pacific: Male ( ZMUC); south of Japan (30°20’N 138°00’E), Dana stn. 4775, 220 m, 11 April 1933 . Female ( SAMA C6876 , ex. JAMSTEC); Japan Trench (38°56.1’N 143°05.6’E), ROV HyperDolphin dive 100, 841 m, 25 April 2002 . S.E. Pacific: Two males & female, male & juv. male ( ZMUC); south-east of Panama (00°18’S 99°07’W), Dana stns. 3558 II, IV & VIII, 2000, 1000 & 100 mw respectively, 18 September 1928 . Juv. ( ZMUC); south-east of Galapagos Islands (04°20’S 116°46’W), Dana stn. 3561 IV, 2000 mw, 24 September 1928 . S.W. Pacific: Juv. ( ZMUC); near Samoa (11°00’S 172°37’W), Dana stn. 3587 V, 2000 mw, 2 November 1928 . Damaged spec. & female ( ZMUC); north of New Zealand (25°47’S 172°24’E), Dana stns. 3621 II & IV, 4000 & 2000 mw respectively, 8 December 1928 . Juv. male ( ZMUC); north-west of Kermadec Islands (27°21’S 175°11’E), Dana stn. 3623 V, 200 mw, 9 December 1928 . Two males ( ZMUC); west of Kermadec Islands (28°17.6’S 177°01’E), Dana stn. 3624 III, 3000 mw, 10 December 1928 . Male ( ZMUC CRU-20412); north of New Zealand (34°24’S 178°42.5’E), Dana stn. 3630 II, 2000 mw, 17 December 1928 . Juv. ( ZMUC); east of New Zealand (41°47’S 176°55’E), Dana stn. 3640 VII, 2500 mw, 7 January 1929 . Male ( ZMUC); east of New Zealand (46°43’S 176°08.5’E), Dana stn. 3642 II, 2500 mw, 9 January 1929 . Male ( ZMUC); west of New Zealand (35°36’S 171°52’E), Dana stn. 3651 VII, 300 mw, 22 January 1929 . Female ( ZMUC CRU-20411); Tasman Sea (33°30.5’S 165°53’E), Dana stn. 3653 VII, 2500 mw, 26 January 1929 . Male ( ZMUC); Tasman Sea (33°26’S 157°02’E), Dana stn. 3656 II, 4000 mw, 29 January 1929 . E. Indian: Three males ( ZMUC); off Sumatra (00°55.5’S 98°15.5’E), Dana stn. 3822 I, 200 mw, 14 September 1929 .

Diagnosis. Females: Body length up to 25 mm, reaching sexual maturity at about 18 mm. Pereon of very mature specimens greatly inflated due to enlargement of pereonites 1–4 (5). Antennae 1 as long as head and first 2.5 pereonites combined (medially). Antennae 2 much reduced in length. Gnathopod 1; basis length about 0.6x remaining articles combined; carpus slightly shorter than propodus, both armed with relatively long, fine setae on posterior margin, also on anterior margin and medially of propodus; posterior margin of propodus with slight excavation and stronger setae distally; dactyl length 0.2–0.3x propodus. Gnathopod 2 slightly longer than G1; basis length about 0.8x remaining articles combined; carpus relatively short, length only two-thirds propodus, both armed with some slender setae on posterior margin; propodus expanded distally with distinct postero-distal excavation (variable in depth) and pairs of stronger setae on postero-distal corner to accommodate dactyl; dactyl strong, curved, length almost 0.4x propodus. Pereopods 3 & 4 similar in structure and length; basis length about 1.8x merus; carpus length 1.3x merus; propodus as long as merus; dactyl curved, very short; all articles (except dactyl) armed with short, fine setae on posterior margin and also on anterior margin (except basis), becoming more numerous and slightly curled on propodus. Pereopod 5 similar in length to P4; basis length about 1.7x merus; carpus as long as merus; propodus length 0.7x carpus; dactyl curved, very short; all articles armed with fine setae as for P3 & 4. Pereopod 6 slightly shorter than P5; relative lengths of merus and carpus as for P5; propodus length about 0.6x carpus; dactyl curved, very short; all articles armed with fine setae as for P5. Pereopod 7 slightly shorter than P6; basis length 2.6x merus; carpus length 1.6x merus, often glandular and slightly broader than other articles (merus relatively shorter than in other pereopods); propodus only marginally longer than half of carpus, often glandular; dactyl curved, very short; all articles armed with setae as for P6. Uropoda with relatively slender peduncles and rami; all with inner ramus slightly longer than peduncle. Uropod 1; inner ramus length 1.5x outer, and 1.1x peduncle. Uropod 2; inner ramus length 1.6x outer, and 1.1x peduncle. Uropod 3; inner ramus length 1.2x outer, and 1.3x peduncle; peduncle width marginally more than half length. Telson triangular; length about 0.4x peduncle of U3.

Males: Like females except for the following. Largest male recorded only 10.0 mm (immature). Pereon slightly arched, oval-shaped from dorsal aspect. Antennae 1 as long as head and first six pereonites combined; peduncular articles and callynophore relatively broader. Antennae 2 reduced in immature specimens, about 0.7x A 1 in more mature specimens. Gnathopod 2 as long as G1; basis length 0.7x remaining articles combined; carpus slightly shorter than half propodus. Pereopods 3 & 4; merus relatively shorter and carpus relatively longer; carpus length 1.5–1.6x merus; propodus slightly longer than merus. Pereopod 5 slightly longer than P4. Pereopod 6 slightly shorter than P5 but only marginally shorter than P4; basis length 1.8x merus; carpus slightly longer than merus. Pereopod 7; basis length 3x merus; carpus length 2.7x merus; propodus length half carpus. Uropoda with inner ramus distinctly longer than peduncle. Uropod 1; inner ramus length 1.5x outer, and 1.4x peduncle. Uropod 2; inner ramus length 1.3x outer and peduncle. Uropod 3; inner ramus length 1.2x outer, and 1.6x peduncle; peduncle width slightly more than half length.

Colour, according to Vinogradov and Semenova (1996), “males and females are deep red or cherry-red; juveniles with rosy medial mesosome, pereopod I, II and mouthparts are red; rest of pereopoda and body are translucent and colourless”. Bovallius (1885) records “hyaline, with red spots”.

Remarks. This species is readily distinguished from its congeners by the morphology of the gnathopods, especially the postero-distal excavation of the propodus of gnathopod 2. It is similar to M. loveni in that the pereon of very mature females is grossly inflated, and also in the general morphology of the pereopods and the urosome.

Apart from the morphological variations due to sexual dimorphism and sexual maturity (as noted for M. loveni ), there is considerable variation in the development of the excavation on the propodus of gnathopod 2. In some specimens the excavation can be quite deep with the postero-distal corner more strongly developed, and with stronger, shorter setae to accommodate the dactyl when it is pressed against the propodus. While one might expect this excavation to be more developed in larger or mature specimens, this is not necessarily the case as the excavation can be well-developed in relatively small specimens (8.6 mm) and less well-developed in relatively large specimens (16.6 mm) (see fig. 12). Similarly, gnathopod 1 can be without a noticeable excavation, or it can be slight and similar to gnathopod 2, as illustrated by Bovallius (1889) for the type (see also Stephensen & Pirlot (1931)). In this respect, these specimens might be confused with M. neosphaericus sp. nov., but males of this species are readily distinguished by the habitus, thick cuticle, stronger dactyls and the relatively longer telson. Females are more difficult to distinguish, but the structure of the dactyls of the pereopods seems to be a consistent character. In M. sphaericus the dactyls are weak and semi-colon-shaped, whereas in M. neosphaericus sp. nov. they are a strong, short nail, particularly for pereopod 7.

It is possible that specimens with slight excavations on both gnathopoda, as illustrated for the type by Bovallius (1889), represent the true M. sphaericus and that those specimens with relatively simple first gnathopoda and second gnathopoda, with a deep excavation, represent another species, but at this stage I am unable to readily distinguish them, particularly as the depth of the excavation of gnathopod 2 is variable.

Most of the specimens collected by submersibles from the north-east Pacific were caught while associated with a gelatinous host. Two females (SAMA C6872 & C6874), from off California, and the male (SAMA C6871), from off Baja California (recorded by Gasca et al. (2006), were captured while on the siphonophore Nectadamus diomedeae . The juvenile, from off Pismo Beach, California (SAMA C6873), was caught while on the hydromedusan, Bythotiara sp. The large, but immature, female from the Japan Trench (SAMA C6876; fig. 12), also captured by submersible, was caught while attached to the narcomedusan Solmissus sp.

Distribution. Like M. loveni , this is one of the more commonly collected species of Mimonectes , having been found in all the world’s oceans except the Mediterranean Sea. In the Atlantic previous records are all from the northern part, from as far north as Greenland ( Stephensen 1923) to tropical regions. I cannot find any published record from the South Atlantic but it is included in the South Atlantic fauna by Vinogradov (1999). In the Pacific it has been recorded from various regions, ranging from the Bering Sea and Kuril-Kamchatka region, through the tropics, right down to Antarctic waters (64°03’S 161°59’E) ( Vinogradov 1962). It seems to be rare in the Indian Ocean (like M. loveni ), with only one previous literature record ( Vinogradov 1964), mainly from tropical regions (06°N to 30°S).

The Dana collected this species extensively in the Atlantic and the Pacific Oceans, providing many range extensions with new records for the south-eastern Atlantic and the Tasman Sea. The latter is also a new record for Australian waters. In the Indian Ocean the Dana only collected it from one station, near Sumatra (stn. 3822) suggesting that this species may indeed be rare in this ocean.

According to Vinogradov et al. (1982) this species is usually found in the 200–2000 m range. The Dana collected specimens from a range of depths with 100–5000 mw, but most were collected with around 2000 mw.