Paralomis stevensi, Ahyong, Shane T. & Dawson, Elliot W., 2006

Ahyong, Shane T. & Dawson, Elliot W., 2006, Lithodidae from the Ross Sea, Antarctica, with descriptions of two new species (Crustacea: Decapoda: Anomura), Zootaxa 1303, pp. 45-68 : 59-66

Paralomis stevensi sp. nov. ( Figs. 7–10 )

Paralomis birsteini .— Stevens, 2004: 6, 7 [not P. b i r s t e i n i Macpherson, 1988]. Neolithodes brodiei .— Thatje & Lörz, 2005: 335 [NIWA 3435 only; not N. brodiei Dawson & Yaldwyn, 1970 ].

Type material. HOLOTYPE: NIWA 23843, male (cl 74.6 mm, cw 75.7 mm, tcl 84.0 mm), near Scott I., 65°40.0–36.0’S, 176°21.0–17.0’W, 1688–1924 m, from stomach of Dissostichus mawsoni Norman , RV Avro Chieftain, set #3, D. Stevens, 2 Dec 2003. PARATYPES: NIWA 3435, 1 ovigerous female (badly damaged, cl about 60.8 mm), E of Sturge I., Balleny Is., 67°25.37’S, 165°15.82’E, 1389 m, TAN0402/214, RV Tangaroa , 3 Mar 2004; NMNZ CR10856, 1 male (cl 61.7 mm, cw 62.0, tcl 73.4 mm), Ross Sea, 66°46.90–44.90’S, 172°56.4– 173 °01.70’W, 1846– 1420 m, found on hook, RV Avro Chieftain, 1742/51, Jerry Buirski, 14 Mar 2003.

Diagnosis. Carapace subpentagonal, slightly wider than long; 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 constriction. Scaphocerite with inner and outer spines. Marginal plates of fourth to sixth abdominal somites in with low, angular protrusions in males, and short conical teeth in females. Sixth abdominal somite subquadrate. Mature male chelipeds strongly dimorphic, spinose; major cheliped palm about twice height of minor cheliped. Major cheliped palm of female about 1.3 times height of minor cheliped. Ambulatory legs elongate, spinose; ventral spines of propodi widely spaced; meral length exceeding 6 times height in males, exceeding 4 times height in females; propodal length exceeding 8.5 times height in males, exceeding 6 times height in females; dactyli shorter than extensor margin of propodi; first ambulatory leg about 3 times carapace length in males.

Description. Carapace: Subpentagonal, slightly wider than long; surface glabrous, sparsely covered with small, scattered granules. Gastric region convex, elevated, more prominent than other regions, with 5 short conical spines forming pentagon with anteriormost in midline (broken in holotype). Lateral margin of hepatic region with two short conical spines, anterior shorter. Branchial regions with 12–14 short marginal spines; surface with 4 or 5 short conical spines in addition to low, scattered tubercles. Cardiac region subtriangular, with 2 pairs of short conical spines forming square. Intestinal region sparsely granular. Pterygostomian region sparsely granular, with prominent anterior spine.

Rostrum and orbit: Rostrum 0.1–0.2 carapace length; broadest basally, without constriction; median spine conical, smooth ventrally; paired dorsal spines subparallel, directed obliquely upwards. Posterior orbital margin near concave; outer orbital spine reaching to base of cornea. Anterolateral spine shorter than outer orbital spine, with low marginal granule midway between outer orbital spine and anterolateral spine.

Ocular peduncle: Longer than cornea; with 2–5 dorsal granules.

Antennule: Peduncle unarmed, reaching anteriorly beyond antennal peduncle by about three­quarters length of distal antennular peduncle segment.

Antenna: Basal antennal segment with small anterolateral spine. Second segment with angular to sharp inner distal margin; outer margin with small basal granule and slender spine that slightly overreaches end of fourth segment. Third segment unarmed. Scaphocerite slender, reaching to midlength of fifth segment in males or to distal threequarters in female, with 1 or 2 short inner spines and 1 or 2 outer spines. Fourth segment unarmed, about half­length of fifth segment.

Abdomen of male: Somites sparsely granular. Second somite with small, widely separated spines along margins. Third somite median plate unarmed; lateral plates with low, irregular, triangular teeth on lateral margin (apices broken in holotype); marginal plates absent, apparently undifferentiated. Fourth and fifth somites with unarmed median and lateral plates; marginal plates undivided, with 2–4 low angular protrusions. Sixth somite as long as or longer than wide, subquadrate, with pair of small distal teeth; marginal plates short, triangular. Telson wider than long, rounded.

Abdomen of female: Somites sparsely granular. Second somite with small, widely separated spines along margins. Lateral margins of third to fifth somites lined with short conical teeth. Sixth somite longer than wide, subquadrate, with pair of small blunt distal teeth. Telson wider than long, rounded.

Chelipeds: Chelipeds with similar spination in both sexes, size strongly dimorphic in males. Major cheliped of males 1.6­1.8 times carapace length, palm strongly inflated, about twice height of minor cheliped palm; minor cheliped slender, 1.5­1.6 times carapace length. Chelipeds of female unequal, major cheliped palm about 1.3 times height of minor cheliped palm; both chelipeds about 1.4 times carapace length. Coxae smooth, unarmed; distal margins with dense tufts of setae. Ischiobasis with 4–7 stout, apically setose ventral spines. Merus with smooth lateral and mesial margins; dorsal and ventral margins spinose, inner distal spine largest. Carpus with prominent spines on dorsal and lateral surfaces; dorsal margin with row of 3–5 spines; mesial margin with two spines, proximal largest; ventral surface with 3 spines. Upper palm length of males 1.1–1.2 times height (major chela) and 2.0 times height (minor chela), of female 1.2 times height (major chela) and 1.3 times height (minor chela); mesial margin with 5 spines, other surfaces with promiment, apically setose tubercles acute tubercles. Fingers with short basal spine and rows of tufts of golden setae. Fingers of major chela with occlusal margins corneous for distal third, proximally with 3 low calcareous prominences; dactylus dorsal margin convex, length subequal to dorsal margin of palm in males, 1.3 times dorsal margin length in female. Fingers of minor chela with occlusal margins corneous for distal third, proximally crenulate; dactylus dorsal margin convex, 1.6 times longer than upper margin of palm in males, 1.4 in female.

Ambulatory legs: Similar, slender, elongate, segments spinose. Coxae smooth, unarmed; distal margins with dense tufts of setae. Ischiobasis with 4 or 5 apically setose ventral spines. Merus ovate in cross­section, almost as long as to slightly longer than carapace in males, about 0.7 cl in female, 6.4–7.7 times longer than high in males, 4.2–4.7 in female; extensor margin with 9–11 spines in addition to paired distal spines; dorsal surface with 5–8 spines; flexor margin with 2 rows of 4 or 5 spines; merus of second ambulatory leg slightly longer than first and third. Carpus slightly longer than half merus length, subcircular in cross­section; extensor margin with 6–8 subequal spines; dorsal surface with 6–8 spines; flexor margin unarmed. Propodus dorsoventrally flattened; about 0.9 merus length, 8.5–9.6 times longer than high in males, 6.1–6.7 in females; with 11–14 spines on extensor margin; dorsal surface with small scattered spines; flexor margin with 7 or 8 spines. Dactylus broadly curved; shorter than extensor margin of propodus; surface with tufts of setae; extensor margin with 3 or 4 apically corneous spines proximally; lateral proximal surfaces with short, distinct sulcus, flanked ventrally by small, corneous spine; flexor margin lined with corneous spinules. First ambulatory leg 2.8–3.2 times carapace length in males, 2.1 in female.

Colour in life. Orange­red.

Etymology. Named in honour of Darren Stevens, NIWA, who collected the holotype of the new species.

Remarks. Of the known species of Paralomis , P. stevensi sp. nov. most closely resembles P. birsteini Macpherson, 1988 (type locality: Ross Sea) and to a lesser extent, P. spectabilis Hansen, 1908 (type locality: off Iceland) in carapace ornamentation whereby the primary spines are low and simple, and the surface between the primary spines is smooth or sparsely granular. The new species resembles P. birsteini and differs from P. spectabilis in the non­pedunculate rostrum and in the armed versus unarmed inner margin of the scaphocerite. Paralomis stevensi differs from P. b i r s t e i n i in the following features:

1) The dactyli of the ambulatory legs are shorter rather than slightly longer than the extensor margin of the propodi ( Figs. 5 , 8 C).

2) In mature males, the right cheliped is considerably more strongly inflated than the left (compare Figs. 7 A, 9B, C). The right palm of P. stevensi is about twice the height of the left, in contrast to P. birsteini in which the right palm is not more than 1.6 times that of the left. In female P. stevensi , the right palm is about 1.3 times the height of the left compared to 1.1–1.2 in P. birsteini .

3) The ambulatory legs of male P. stevensi are considerably longer and more slender than in P. birsteini of similar size. In comparing the holotype of P. stevensi (cl 74.6 mm, cw 75.7 mm) with the large male of P. birsteini (cl 79.4 mm, cw 76.4 mm), the following morphometric differences are evident. The meri of the ambulatory legs in P. stevensi are longer rather than shorter than carapace length (1.1 versus 0.8–0.9), and also more slender than in P. birsteini (exceeding seven versus about five times height). The propodus length in P. stevensi exceeds nine times the height whereas in P. birsteini , the propodus length is less than seven times the height. The first ambulatory leg of P. stevensi exceeds three times the carapace length (3.2 cl) compared to less than 2.7 times carapace length in P. birsteini . Note that allometric effects should be considered when using ambulatory leg morphometrics to separate P. stevensi from P. b i r s t e i n i. In the male paratype of P. stevensi (cl 61.7 mm, cw 62.0 mm), the length of the first ambulatory leg and proportional lengths of segments approach that of the largest specimen of P. b i r s t e i n i examined (cl 79.4 mm, cw 76.4 mm).

4) The marginal plates of the fourth to sixth abdominal somites in male P. stevensi are lobulate or angular but not sharply toothed as in P. birsteini ( Figs. 6 B, 10).

The two male specimens of P. stevensi agree well morphologically. Aside from allometric differences in relative lengths of the ambulatory legs ( Table 1 ) and acuity of carapace spines, the holotype differs from the paratype in the length of the sixth abdominal somite (as long as wide in the paratype, longer than wide in the holotype) and spination of the scaphocerite. The scaphocerite bears one inner and two outer spines in the holotype and one outer and two inner spines in the paratype, reminiscent of variation in the type series of P. birsteini . Unfortunately the female paratype of P. stevensi is badly damaged, having been crushed and dismembered during collection. Nevertheless, enough of the female paratype remains to show that it differs from males in cheliped and ambulatory leg proportions, being less inflated and shorter, respectively, approaching P. birsteini and P. spectabilis . Nevertheless, female P. stevensi are readily distinguished from both sexes of P. birsteini by the distinctly shorter dactyli of the ambulatory legs, and from P. spectabilis by the armed versus unarmed inner margin of the antennal scaphocerite.

The holotype of P. stevensi was taken from an Antarctic toothfish stomach. Though the third and fourth ambulatory legs are damaged, the otherwise intact condition of the specimen indicates that it was swallowed whole.

Distribution. Presently known only from the Ross Sea, Antarctica, at depths between 1389 and 1924 m.

Figures

FIGURE 5. Paralomis birsteini Macpherson, 1988, male (cl 79.4 mm, cw 76.4 mm, NIWA 24217). A, overall dorsal view. B, overall ventral view.

FIGURE 6. Paralomis birsteini Macpherson, 1988, male (cl 79.4 mm, cw 76.4 mm, NIWA 24217). A, carapace, dorsal view. B, abdomen. C, right chela, outer surface. D, left chela, outer surface.

FIGURE 7. Paralomis stevensi sp. nov., male holotype (cl 74.6 mm, cw 75.7 mm, NIWA 23842). A, overall dorsal view. B, anterior carapace, dorsal view.

FIGURE 8. Paralomis stevensi sp. nov., male holotype (cl 74.6 mm, cw 75.7 mm, NIWA 23842). A, carapace, dorsal view. B, right antenna, dorsal view. C, right first ambulatory leg and proximal portion of second and third ambulatory legs, dorsal view. D, dactylus of right first ambulatory leg, dorsal view.

FIGURE 9. Paralomis stevensi sp. nov., male holotype (cl 74.6 mm, cw 75.7 mm, NIWA 23842). A, carapace, right lateral view. B, right chela, outer surface. C, left chela, outer surface.

FIGURE 10. Paralomis stevensi sp. nov., male holotype (cl 74.6 mm, cw 75.7 mm, NIWA 23842). A, ventral view. B, distal portion of abdomen.