Pycnogonum papua, 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 : 208-210

Pycnogonum papua n. sp.

( Fig. 5 )

HOLOTYPE. — 1 ♀, MNHN-IU-2011-2545; Stn.CP 3761, Vicinity of the Feni Islands, Papua New Guinea, 03°59’S, 153°56’E, 760-823 m, 14.XI.2010, coll. Samadi & Corbari.

PARATYPE. — 1 ♀, MNHN-IU-2012-492, Stn. CP3762, Vicinity of the Feni Islands, Papua New Guinea, 03°57’S, 153°49’E, 995-1050 m, 14.XI.2010, coll. Samadi & Corbari.

ETYMOLOGY.— The name is derived from the vicinity of its type-locality, Papua New Guinea (noun in apposition).

DESCRIPTION OF FEMALE HOLOTYPE

Relatively large Pycnogonum , trunk length 4.5 mm, width 2.6 mm, leg span approximately 14 mm. Cuticle sculptured with subtle reticulation and numerous small pimples, commonly in pairs (as indicated for tibia 1 on Fig. 5 C ). Trunk ( Fig. 5 A, B ) fully segmented, glabrous, but with mid-dorsal tubercles at posterior rim of segments 1 to 3 and centrally on segment 4; lateral processes about 75% as long as segment width, without any dorsodistal tubercles, separated by about half of their own width. Cephalon 30% of trunk length, ocular tubercle tall, distally pointed, 2.5 times as high as wide, without eyes; mid-dorsal tubercle near posterior margin no higher than wide, about one-fifth as tall as ocular tubercle; second and third trunk segments each two thirds as long as cephalon and each with a mid-dorsal pointed tubercle at posterior margin, tubercle on second segment about 0.6 times as tall as ocular tubercle, tubercle on third segment as tall as ocular tubercle; fourth trunk segment slightly longer than third, mid-dorsal tubercle in posterior half distally blunt, about 0.4 times as tall as tubercle on third segment. Abdomen naked, not articulating, held just below horizontal, 0.35 times as long as total trunk length, with rounded postero-dorsal extension.

Proboscis naked, tapering, slightly downcurved ( Fig. 5 A ), 0.8 times as long as cephalon, without tubercles; oral glands (sensu Staples 2002) not seen.

Third leg ( Fig. 5 D ) with few dorsal and ventral (but not lateral) slender spines on margins of all articles (sparse on coxae), not bifurcating (detail from propodus, Fig. 5 D ). Coxa-1 with small ventrodistal tubercle and one dorsodistal spine; coxa-2 slightly longer than coxa-1, coxa-3 about as long as coxa-1; femur longest article, 3.6 times as long as wide, with two small rounded dorsodistal tubercles but no spur, ventral margin with slight raised tubercles in proximal half, each bearing stout spine (detail, Fig. 5 D ); tibia-1 0.9 times as long as femur, four times as long as wide; tibia-2 0.8 times as long as femur, 4.7 times as long as wide; tarsus short, one-quarter as long as propodus, longer ventrally than dorsally, with slender ventral spines; propodus slender, 3.9 times as long as wide; main claw 0.6 times as long as propodus; auxiliary claws absent. Gonopores distinct on postero-dorsal margin of coxa 2 of fourth legs. Coxal glands (sensu Staples 2002) not seen.

Measurements of holotype (mm): trunk length 4.5; width across second lateral processes 2.6; proboscis length 3.74; abdomen length 1.57; third leg, coxa-1 0.78, coxa-2 0.96, coxa-3 0.87, femur 3.04, tibia-1 2.78, tibia-2 2.35, tarsus 0.30, propodus 1.35, claw 0.78.

REMARKS

The present species, with its conspicuous dorsal trunk tubercles, lack of auxiliary claws and tapering proboscis, keys out in Stock’s (1966) key to the genus to either Pycnogonum tenue Slater, 1879 (not Kishida, 1927 as given by Stock, 1996) or Pycnogonum occa Loman, 1908 . Unlike Pycnogonum papua n. sp., Pycnogonum tenue has blunt trunk tubercles, a domed ocular tubercle, a dense brush of spinules ventrally on the propodus and more compact longer leg-articles (e.g., tibia-1 about twice as long as wide) (see Nakamura 1987), while P. occa has distinct dorsodistal tubercles on each lateral process, as well as a larger posterior tubercle on the cephalon and a proportionately shorter proboscis (see Loman 1908; Staples 2002, including comprehensive discussion of this species).

Twenty-eight species of Pycnogonum have been described since Stock (1966) ( Bamber & El Nagar 2012), six of which have auxiliary claws (see Bamber 1997). Of the remainder, the only species with a tapering proboscis, a pointed ocular tubercle and pointed mid-trunk tubercles is Pycnogonum moniliferum Stock, 1991 (q.v.; see also Bamber 2004a), but, unlike P. papua n. sp., that species has no dorsal tubercle on the fourth trunk segment and far-more compact and nodulose longer leg-articles (e.g., tibia-1 twice as long as wide).

Pycnogonum papua n. sp. was taken off Papua New Guinea in a depth range of 760-1050 m.

Figures

FIG. 5. — Pycnogonum papua n. sp., female holotype (MNHN-IU-2011-2545): A, habitus, lateral; B, habitus, dorsal; C, distal half of tibia 1 of third leg, showing detail of cuticular sculpture; D, third leg. Scale bar: A, B, D, 4 mm; C, 1.33 mm.