Sericosura conta, Bamber, Roger N., 2009

Bamber, Roger N., 2009, Two new species of Sericosura Fry & Hedgpeth, 1969 (Arthropoda: Pycnogonida: Ammotheidae), and a reassessment of the genus, Zootaxa 2140, pp. 56-68 : 57-59

Genus Sericosura Fry & Hedgpeth, 1969

Sericosura conta sp. nov. ( Fig. 1 )

Material examined: female holotype ( NMW.Z.2005.016.1), HABMAP Station 6, Irish Sea off Arklow, 52°57.918’N 005°52.495’W to 52°58.096’N 005°52.589’W, “stony ground”, 22.7 m depth, Tjärnö dredge sample, 26 July 2005.

Description: generally typical of Sericosura ; trunk ( Fig. 1 A, B) compact, fully segmented, segments raised (flared) at segment articulations. Cephalon expanded anteriorly, constricted anterior to first lateral processes, 0.52 times total trunk length, without ornamentation; ocular tubercle a hardly-distinguishable slight dome near anterior margin, without eyes; palp, chelifore and proboscis attachment on anterior face of cephalon. Lateral processes without tubercles, with single fine, curved spines on anterior and posterior faces, processes 1 and 2 nearly touching, processes 2 and 3 not separated, processes 3 and 4 separated by less than their own diameter; first lateral process curved anteriorly. Abdomen elongate, downcurved, reaching just past distal edge of coxa 1 of leg 4, with distinct basal articulation, bearing laterodistal and dorsodistal slender curved spines.

Proboscis stout, barrel-shaped, with very slight central constriction, naked, held below cephalon and directed ventrally, 0.6 times as long as trunk.

Chelifore ( Fig. 1 C) reduced, protruding from the anterior face of the cephalon above the proboscis; scape of one article, shorter than wide, with slender outer distal spine and sparse dorsodistal setae; chela atrophied, globular.

Palp ( Fig. 1 D) of nine articles. First article (P1) short, wide, compact; P2 elongate, 4.4 times as long as P1, naked; P3 as long as P1 with sparse dorsal setae; P4 as long as P2, slightly downcurved, with sparse dorsal and paired ventrodistal setae; P5 to P9 short, subequal (P5 longest, P9 shortest), ventrally densely setose as figured, together 0.6 times as long as P4.

Ovigers damaged, presumably of ten articles, only basal five articles retained ( Fig. 1 E), article 2 ( O 2) longest, O 1 and O 3 subequal, O 4 and O 5 respectively 0.8 and 0.63 times as long as O 2; articulations with O 3 anaxial.

Third leg ( Fig. 1 F) elongate, not slender. Coxa 1 compact, with anterodistal and posterodistal slender curved spines; coxa 2 1.5-times length of coxa 1, ventrally with single subdistal gonopore, and with small middorsal tubercle; coxa 3 0.9 times as long as coxa 2, wider distally, with fine ventral setae; femur sparsely setose, 3.5 times as long as coxa 3. Tibia 1 as long as femur, sparsely setose, proximally angled to articulation with femur; tibia 2 just longest article, 1.03 times as long as tibia 1, more densely setose, more slender, proximally angled to articulation with tibia 1. Tarsus ( Fig. 1 G) small, subtriangular, with dense ventral setae and paired dorsal setae on distinct spur. Propodus without heel or proximal spines, sole with numerous marginal setae, dorsal setation sparse; main claw one-third length of propodus, auxiliary claws conspicuous, slender, as long as main claw. Other legs identical.

Note: the present specimen is clearly mature, and is assumed to be a female owing to the absence of any trace of a cement gland, and the comparatively swollen morphology of the femora.

Measurements of holotype (mm): Trunk length (anterior of cephalon to posterior tip of fourth lateral process): 5.58; cephalon: 2.92; trunk segment 2: 0.86; trunk segment 3: 0.75; width across 2nd lateral processes: 3.08; abdomen length: 1.92; proboscis length (lateral): 3.42.

Lengths of palp articles 1 to 9 respectively: 0.39; 1.66; 0.40; 1.62; 0.25; 0.18; 0.22; 0.18; 0.16.

Third leg, coxa 1: 0.92; coxa 2: 1.38; coxa 3: 1.25; femur: 4.33; tibia 1: 4.33; tibia 2: 4.50; tarsus: 0.28; propodus: 1.58; main claw: 0.56; auxiliary claw: 0.56.

Etymology: from the Greek kontos, meaning short, referring to the very truncated chelifore scape of the present species, distinct from the other described species.

Remarks: There are two previously-described species of Sericosura , as well as Ammothea verenae , which have a nine-articled palp, all from the North Pacific, viz. S. dissita and S. cochleifovea . The other described Sericosura species have a seven-articled palp.

The female of S. cochleifovea has long setae on the abdomen, the lateral processes and the tibiae and propodi of the walking legs (the male has a long proximal femoral cement-gland tube); the proboscis is clavate. S. dissita has a proportionately longer abdomen and a more slender main claw. Both of these species have a proportionately more slender coxa 2 (nearly twice as long as coxa 1), and a prominent ocular tubercle.

Sericosura conta sp. nov. is closest to A. verenae , which shows variation in its ocular tubercle from a small bifurcate tubercle to a very low dome; the proboscis of A. verenae has submedian and subdistal constrictions, and the second palp article is much longer than the fourth. Unlike S. conta , all three of these previous species have their lateral processes separated by at least one-quarter of their diameters, auxiliary claws shorter than their main claws and chelifore scapes at least twice as long as wide.

Thus, S. conta is the shallowest recorded species of the genus, the only species outside the Pacific to have a nine-articled palp, and shows the most compact trunk morphology and the most reduced chelifore; S. conta is the only species of Sericosura with auxiliary claws as long as the main claw.

The habitat at the type-locality is clearly not a hydrothermal vent, but the presence of a hydrocarbon seep at this site is a possibility (see Croker 1995).

Figures

FIGURE 1. Sericosura conta sp. nov., A, body dorsal; B, body posterolateral; C, chelifore; D, right palp; E, basal five articles of oviger; F, third right leg; G, distal articles of third leg. Scale line = 3 mm for A, B, F, 1.3 mm for D, 1 mm for G.