Hyperoche luetkenides Walker 1906

Hyperoche luetkenides Walker, 1906

(Figs. 8–10)

Hyperoche luetkenides Walker, 1906: 453.— Walker 1907: 8, pl. 1, fig. 2. Barnard 1930: 415 (key). Hurley 1969: 33, pl. 19 (map 5). Vinogradov et al. 1982: 282 (key), 289. Barkhatov & Vinogradov 1988: 167, 168 (table). Weigmann-Haass 1991: 170 –176, 177 (map), figs. 1–27. De Broyer & Jażdżewski 1993: 114. Vinogradov & Semenova 1996: 618. Barkhatov et al. 1999: 808 (table), 809–810. Vinogradov 1999: 1146 (table), 1186 (incl. key). Zeidler 2004: 29. Zeidler & De Broyer 2009: 46, fig. 14 (distribution). Zeidler & De Broyer 2014: 304, map 11.

non [mis-identification = Hyperoche capucinus]— Monod 1926: 49–50, figs. 47–48.

Hyperoche medusarum [mis-identification]— Barnard 1932: 276. Hardy & Gunther 1935: 195, 197. Hurley 1955: 144 –147, figs. 96–114. Hurley 1960: 112. Hurley 1969: 33, pl. 19 (maps). Lipskaya 1980: 13 –14. Ramirez & Vinas 1985: 32 –33, figs. 3–4. Jażdżewski & Presler 1988: 63 & 69 (tables), 66, figs. 1–2. Torres et al. 1994: 210 –211 (incl. table).

Hyperoche cryptodactylus Stebbing, 1888: 1399 –1402, pl. 170.— Bovallius 1889: 86 (key), 105–106. Walker 1904: 236. Steuer 1911: 674 (key). Dick 1970: 36 (key), 57, fig. 6. Vinogradov et al. 1982: 283 (key), 285–286, fig. 144. Vinogradov 1999: 1146 (table), 1186 (incl. key), fig. 4.106. NEW SYNONYMY.

non [mis-identification = H. medusarum]— Gasca 2009b: 217 (table). Lavaneigos & Hereu 2009: 142, 151 (appendix).

Type material. The unique holotype male (12 mm) of Hyperoche luetkenides is in the NHM, London (1907.6.13.4 & 5); on two microscope slides. The type locality is the Pacific Sector of the Southern Ocean, south of Macquarie Island [57°25’30”S 151°43’E], Discovery stn.

Type material of synonyms. The unique holotype male (about 7 mm) of Hyperoche cryptodactylus is in the NHM, London (89.5.15.224); on two microscope slides. The type locality is the south-east Atlantic, off the Cape of Good Hope [34°41’S 18°36’E], Challenger stn. 141, surface, 17 December 1873.

Diagnosis. Females: Sexually mature at about 14–18 mm. Antennae 1 as long as head, about 1.3 x A2. Head length equal to first two pereonites combined. Pereon globular, length almost 1.6 x pleon. Gnathopod 1; basis marginally shorter than remaining articles combined, relatively broad with maximum width about half length; merus spoon-shaped, projecting under carpus to slightly beyond base of propodus, with fringe of setae on distal margin; carpal process extends beyond distal margin of propodus to middle of dactylus or more, anterior margin denticulate; posterior and distal margin of propodus also denticulate; dactylus slightly curved, posterior margin finely denticulate, length almost half propodus. Gnathopod 2 slightly longer than G1 but similar in structure except for marginally shorter spoon-shaped process of merus. Pereopods 3 & 4 similar in length to P5 & 6, or marginally shorter. Pereopod 3; basis length 2.6 x merus; carpus with postero-distal corner produced into distinct tooth with denticulate margins, length 1.3 x merus and 0.8 x propodus; posterior margin of propodus denticulate; dactylus length slightly more than 0.2 x propodus. Pereopod 4 slightly more slender than P3 but similar in structure, except the postero-distal corner of the merus is rounded. Pereopods 5 & 6 are similar in size and structure; basis length about twice merus; carpus length about 1.3 x merus, marginally shorter or equal to propodus; dactylus length slightly more than 0.3 x propodus. Pereopod 7; coxa fused with pereonite; similar in structure to P6 but slightly shorter because merus and carpus are relatively shorter. Epimeral plates with postero-distal corner produced into small point. Uropod 1; peduncle not reaching to limit of peduncle of U2 and to slightly less than half peduncle of U3; inner ramus marginally longer than outer, slightly shorter than peduncle. Uropod 2; inner ramus slightly shorter than peduncle, about 1.4 x length of outer ramus. Uropod 3; inner ramus marginally longer and wider than outer, about half-length peduncle. Telson triangular, as long as wide, about 0.4 x length of peduncle of U3.

Colour in life: red-brown all over except for urosomites 2–3 and the uropoda; these clear with few brown spots; eyes pale green (pers. obs.).

Males: Sexually mature at about 15–18 mm. Antennae slightly longer than entire animal. Pereon and pleon slender, of similar length. Appendages generally more slender than in females, especially the gnathopoda, otherwise very similar in structure and relative lengths of articles, except for the following minor variations. Gnathopoda with merus not projected as far under the carpus. Pereopods 3 & 4 with postero-distal corner of the carpus more prominent and pointed. Epimeral plates relatively much longer and deeper. Uropod 1; peduncle extends to limit of peduncle of U2; both rami with characteristic proximal excavation. Telson as wide as long, slightly shorter than 0.4 x length of peduncle of U3.

Material examined. The unique types of Hyperoche luetkenides and H. cryptodactylus as detailed above and the following additional material.

Antarctic, Atlantic Sector: Female (USNM 301630), south of the Falkland Islands [54°40’S 58°58’W to 55°06’S 59° 00’W], R/V Eltanin (USARP) cruise 6, stn. 348, 644 m, University of Southern California, 4 December 1962. Antarctic, Indian Sector: Juvenile male (SAMA C3765), off Wilkes Land [65°10’S 109°32’E], BANZARE stn. 96, 2200 mw, 26 January 1931. Six females (4 lots, SAMA C7975–7938), Prydz Bay [range 66°32’– 68°30’S 68°51’– 74°57’E], WZ on Aurora Australis (ANARE), 48–800 m, January/ February 1991. Antarctic, Pacific Sector: Female (SAMA C7939), west of Macquarie Island [54°50.5’S 158°40.1’E to 54°41.9’S 158°43’E], CSIRO FRV Southern Surveyor stn. SS01/ 52, 959.6 m, 22 January 1999. Antarctic Peninsula: Male (USNM 1090279), Palmer Archipelago, Cobalescou Island towards Alcock Island [64°11’11”S 61°35’24”W], R/V Hero (USARP), Cruise 721, stn. 303, 100– 150 m, Smithsonian Oceanographic Sorting Center, 16 December 1971.

Remarks. This is one of the largest species of Hyperoche, reaching sexual maturity at about 14–18 mm. The close morphological similarity of this species to H. medusarum, and the minor characters that distinguish it, have already been discussed under that species. One might have considered it a synonym of H. medusarum, thus making it a bi-polar species. However, it is more likely that the two species evolved from a common ancestor that was once more widespread in the Atlantic, in the past, when conditions there were much colder. As conditions became warmer the two populations became geographically isolated and evolved into separate species. This scenario is similar to that proposed for Primno macropa and P. abyssalis by Bowman (1985). Future genetic studies may help to resolve this issue, but for the time being it seems best to recognise H. luetkenides as a valid species restricted to the colder waters of the Southern Hemisphere with H. medusarum a cold-water Northern Hemisphere species.

Regarding the validity of H. cryptodactylus, this species was described from an imperfect, juvenile male specimen, and is distinguished from its congeners by the retractile dactylus of gnathopod 2. However, the validity of this species is very doubtful in view of the current finding regarding the occurrence of retractile dactyls of pereopoda for several specimens of H. medusarum (Fig. 3), and also for the second gnathopod of a female specimen of H. luetkenides (Fig. 9). Stebbing (1888) illustrated the second gnathopod from the right with a retractile dactyl but did not mention the status of the one on the left, which judging by his illustration of the habitus, does not have a retractile dactyl, similar to that found in the specimen of H. luetkenides illustrated here (Fig. 9). An examination of the type has confirmed this observation. Thus, H. cryptodactylus, which is otherwise indistinguishable from H. luetkenides, must be considered synonymous. This would make it the senior synonym and present a potential nomenclatural problem. However, apart from the dubious record of Walker (1904), all previous literature records of H. cryptodactylus refer to Stebbing’s (1888) account of the unique type. The specimen recorded by Gasca (2009b) having been re-examined (Gasca pers. com. Feb. 2014) and re-identified as a moulting juvenile of H. medusarum. Records of H. luetkenides, on the other hand, refer to a relatively rare, but better known, Antarctic /sub-Antarctic species. Thus, nomenclatural stability would be best served, in this instance, by the suppression of the specific name “ cryptodactylus ” in favour of “ luetkenides ”, especially since the name was constructed to reflect the retractile dactyl of gnathopod 2, which has been demonstrated here to be an invalid specific character for Hyperoche. Thus, its future use for the species in question would also be misleading.

A gelatinous plankton associate has not been recorded for this species.

Distribution. A relatively rare species restricted mainly to the region between the Antarctic Polar Front and the Antarctic Continent, sometimes occurring further north with the incursion of colder water. Reliable records are from the Weddell Sea, Scotia Sea, Prydz Bay, off Wilkes Land and near Macquarie Island. The most northerly record is the type locality for H. cryptodactylus, from off South Africa; it’s occurrence there probably due to an influx of cold water to that region. The few available catch records suggest that it inhabits near-surface waters.