Pycnogonum staplesi, Bamber, 2013

Bamber, Roger N., 2013, Deep-water Pycnogonida from recent cruises to Papua New Guinea and Melanesia, with an appendix of new records from Polynesia and descriptions of five new species, Zoosystema 35 (2), pp. 195-214 : 210-212

Pycnogonum staplesi n. sp.

Pycnogonum occa Stock, 1997: 407 . Non Pycnogonum occa Loman, 1908 : fig. 6.

MATERIAL EXAMINED. — 1 “ ♀ ”, holotype MNHN-Py 922, New Caledonia, Stn DW923, 18°51.51’S, 163°24.17’E, 502- 470 m depth, 06.VIII.1994.

ETYMOLOGY. — Named after David Staples, in recognition of his comprehensive work on the morphology of Pycnogonum species , inter alia.

DESCRIPTION OF HOLOTYPE

Trunk length 2.9 mm, width 2.1 mm, leg span approximately 12 mm. Cuticle sculptured throughout with small warts.Trunk ( Fig.6A, B ) fully segmented, glabrous; lateral processes about 85% as long as segment width, separated by about half of their own width, each bearing fleshy dorsodistal tubercle about 1.5 times as tall as lateral-process width. Cephalon 32% of trunk length, ocular tubercle tall, distally rounded, 1.7 times as high as wide, without eyes; mid-dorsal tubercle near posterior margin similar to lateral process tubercles, tapering, just taller than ocular tubercle; second and third trunk segments each two thirds as long as cephalon and each (?) with a slender, fleshy mid-dorsal tapering tubercle at posterior margin, tubercle on second segment broken, tubercle on third segment as tall mid-dorsal cephalon tubercle; fourth trunk segment slightly shorter than third, without mid-dorsal tubercle. Abdomen naked, not articulating, held horizontally, 0.27 times as long as total trunk length, distally blunt.

Proboscis naked, tapering, half as long as cephalon, without tubercles; oral glands (sensu Staples 2002) not seen.

Third leg with sparse dorsal and ventral slender simple spinules on margins of all coxae, femur and tibia 1, dorsally on tibia 2 and propodus (e.g., Fig. 6C ); ventral margins of tibia 2, tarsus and propodus with dense row of distally squared, split spinules ( Fig. 6C ). Coxa-1 without tubercle; coxa- 2 1.3 times as long as coxa-1, coxa-3 just shorter than coxa-2; femur 2.3 times as long as coxa-2, 3.2 times as long as wide, with rounded dorsodistal spur; tibia-1 as long as femur, 2.5 times as long as wide; tibia-2 0.7 times as long as femur, 2.7 times as long as wide; tarsus short, one-quarter as long as propodus, longer ventrally than dorsally; propodus slender, 3.1 times as long as wide, with dorsodistal tuft of three spinules; main claw half as long as propodus; auxiliary claws absent. Gonopores and coxal glands (sensu Staples 2002) not seen.

Measurements of holotype (mm): trunk length 2.91; width across second lateral processes 2.1; proboscis length 1.56; abdomen length 0.8; third leg, coxa-1 0.43, coxa-2 0.57, coxa-3 0.55, femur 1.31, tibia-1 1.31, tibia-2 0.93, tarsus 0.17, propodus 0.68, claw 0.37.

REMARKS

Stock (1997) recorded this specimen, which he attributed to Pycnogonum occa Loman, 1908 , from New Caledonia. Staples (2002), in his analysis of species of Pycnogonum from Australia, discussed the difficulty in interpreting the various records of P.occa in the literature, and in particular noted that Stock (1997) did not comment on the morphology of his specimen, so no comparison with this specimen could be made. Considering the possibility that this New Caledonia specimen might have been actually of the previous species, Stock’s specimen has been re-examined, and determined to be a distinct species.

With its lateral-process tubercles, lack of a middorsal tubercle on the fourth trunk segment, blunt ocular tubercle and peculiar spinulation of the propodus, tarsus and tibia-2, this specimen is not Pycnogonum papua .

Neither is it Pycnogonum occa : in comparison with Loman’s (1908) figures and description, the lateral processes are not sufficiently separated, the ocular tubercle is not spired, the lateral-process tubercles are comparatively enormous, there is no middorsal tubercle on the fourth trunk segment, and, in particular, there is an array of distally squared, split spinules along the propodal sole, the ventral margin of the tarsus and the ventral margin of the distal third of tibia-2 ( Fig. 6C ). While some other species of Pycnogonum have split spines on the legs (e.g., P. clarki Staples, 2002 ; P. coninsulum Bamber, 2008 ), those spinules are distally pointed, not truncate. Loman (1908: pl. XII, fig. 174) clearly shows sparse and simple ventral spinulation on these articles, consistent with the morphology of Staples’ (2002) specimen. In fact, the density of this spinulation is more in agreement with the “ P. occa ” specimen of Stock (1968: 61-62, fig. 22c–e) from the Kermadec Trench, although that specimen does have a tubercle on the fourth trunk segment, and also peculiar tubercles along the frontal margin of the cephalon (the latter precluding it from being P. occa ; see also Child 1988: 27; Staples 2002: 547).

Stock (1997) called the present specimen a female, but I can find no gonopores to confirm or deny this.

Figures

FIG. 6. – Pycnogonum staplesi n. sp., holotype (Py 922): A, habitus, lateral (note, mid-dorsal tubercle on trunk segment 2 broken); B, habitus, dorsal; C, distal articles of third leg, with detail of split spinule. Scale bar: A, B, 3 mm; C, 0.4 mm.