Paralomis birsteini Macpherson 1988

Paralomis birsteini Macpherson, 1988 (Figs. 5, 6)

Paralomis spectabilis.—Birstein & Vinogradov, 1967: 390, figs. 1, 2— Kirkwood, 1984: 37, fig. 45 [map only].— Tkachuk, 1985: 1733 –1734, figs. A, B.— Zaklan, 2002: 773 [Ross Sea records] [not P. spectabilis Hansen, 1908].

Paralomis birsteini Macpherson, 1988a: 72 –74, figs. 4, 5a–e [type locality: Scott Island, Ross Sea, Antarctica, 67°29’S, 179°55’W].— Arana & Retamal, 1999: 101 [Bellingshausen Sea records].— Stevens, 2004: 6, 7 [part].

Neolithodes brodiei.— Thatje & Lörz, 2005: 335 [NIWA 3432 only; not N. brodiei Dawson & Yaldwyn, 1970].

Material examined. NIWA 3432, ovigerous female (cl 75.0, cw 72.9 mm), Balleny Seamount, 65°28.53–28.97’S, 161°02.88–02.75’E, 760– 750 m, TAN0402/269, RV Tangaroa, 7 Mar 2004; NIWA 24217, 1 male (cl 79.4 mm, cw 76.4 mm), near Scott I., 67°21.01–21.02’S, 179°52.68–52.34’W, 540–600 m, sled tow, TAN0602/394, 6 Mar 2006; NIWA 23842, 1 male (cl 41.4 mm, cw 40.7 mm), 1 female (cl 35.2 mm, cw 32.5 mm), both infected with Briarosaccus callosus Boschma, 1930 (Rhizocephala), near Scott I., 64°31.0–30.0’S, 171°14.0–08.0’W, 1225–1617 m, from stomach of Dissostichus mawsoni Norman, 1937, Avro Chieftain, set #24, 17 Dec 2003; NMNZ CR11000 1 male (cl 76.9, cw 73.4 mm), Ross Sea, Trip #1862, haul 147, area 88.1G, RV San Aotea, obs. S. Voice [note: specific station data not available]; NMNZ CR11001 1 male (cl 79.8, cw 74.7 mm), 1 female (cl 61.7, cw 59.4 mm), both infected with Briarosaccus callosus Boschma, 1930 (Rhizocephala), near Scott I., 68°23–21’S, 179°53–57’E, 1337– 1050 m, RV San Aotea II, trip 2010, haul 137B, on hook, B, E. Winslade, 31 Jan 2005.

Diagnosis. Carapace subpentagonal, slightly longer than wide; surface glabrous, sparsely covered with small, scattered granules and short conical spines, including median gastric spine; lateral margins with short conical spines. Rostrum trispinose, broadest basally, without basal constriction. Scaphocerite with 1 or 2 short inner basal spines and 1 or 2 outer spines. Marginal plates of fourth to sixth abdominal somites with acute, conical teeth in males. Male chelipeds dimorphic, spinose; major cheliped palm height less than 1.6 times that of minor cheliped. Ambulatory legs elongate, spinose; ventral spines of propodus widely spaced; merus about 5 times longer than high; propodus length not exceeding 7.5 times height; dactylus longer than extensor margin of propodus; first ambulatory leg about not exceeding 2.7 times carapace length.

Remarks. The specimens agree well in most respects with the type description, differing in having the median rostral spine distinctly overreaching the dorsolateral spines as figured by Arana & Retamal (1999: fig. 2) for a specimen from the Bellingshausen Sea. As expected, the general spination of larger specimens is less pronounced than in smaller specimens, the proportional lengths of the ambulatory legs vary with size and sex, and the size and form of the right chela is distinctly sexually dimorphic. In addition, the sixth abdominal somite is longer than wide in the two smallest specimens, but variable in the largest specimens, ranging from as long as wide to longer than wide. The ambulatory legs of the largest male are longer than those of the ovigerous female (2.6–2.7 versus 2.2–2.3 cl), and their respective meri and propodi follow a similar pattern (0.8–0.9 and 0.7–0.8 cl versus 0.7 cl and 0.6–0.7 cl). The ambulatory legs of the smallest specimen are comparatively shortest (ambulatory legs 2.0 cl and meri 0.6–0.7 cl). The right crushing claw of the adult males measure up to 1.6 times the height of the more slender left palm whereas the chelae of the females (small to large) are similar and slender with the right palm height 1.2 times that of the left.

The two specimens collected from the stomachs of the Antarctic toothfish (Dissostichus mawsoni Norman, 1937) were probably swallowed whole in view of their nearly complete condition.

Several specimens of P. birsteini are infected by the rhizocephalan Briarosaccus callosus Boschma. Briarosaccus callosus was first reported as a parasite of P. birsteini (as P. spectabilis) by Tkachuk (1985) based on specimens from the vicinity of the Crozet Islands (approximately 52°S, 41°E). The present records of B. callosus from P. b i r s t e i n i are the first from the Ross Sea.

Paralomis birsteini closely resembles P. stevensi sp. nov., described below; distinguishing features are discussed under the account of the latter.

An undetermined species of Paralomis, possibly referable to P. birsteini but differing subtly in “armature of the rostrum, scaphocerite and ambulatory legs” is known from Tasmanian seamounts (Poore et al. 1998: 72; Poore 2004). Whether the Tasmanian specimens represent P. birsteini, P. stevensi or another species remains to be determined.

Distribution. The Ross Sea, Bellingshausen Sea, Crozet and Kerguelen islands; 500–1876 m (Macpherson 2004).

Species Sex cl Ambulatory Merus Merus Propodus Propodus (mm) leg length/cl length/cl length/height length/cl length/height