Ascorhynchus constrictus Stock, 1997

Bamber, Roger N, 2011, The male of Ascorhynchus constrictus Stock, 1997 (Arthropoda: Pycnogonida), with further new records of deep-sea pycnogonids from New Caledonia, the Solomon Islands and Vanuatu, Zootaxa 2787, pp. 55-67 : 56-58

Ascorhynchus constrictus Stock, 1997

Fig. 1

Stock, 1997, 391–393, fig. 2

Material. Solomon Islands: 13 (Registration No. MNHN-IU-2007-4730), station CP2230, 6°27.8’S 156°24.3’E, XI 2004, depth 837–945 m, Solomon Island, NW Choiseul. Bouchet, Warén & Samedi-IRD coll.

Description of male. Broadly similar to the female (vide Stock, 1997). Integument finely pitted. Trunk ( Fig. 1 A), cephalon and lateral processes without any tubercles, but single long, slender setae arising mid-dorsally on posterior margin of cephalon and trunk segments two and three; cephalon widest at mid-length at point of attachment of ovigers, widened anteriorly at point of attachment of chelifores and palps; ocular tubercle absent. Abdomen articulated, slender, reaching distal margin of coxa 1 of fourth leg. Proboscis with conspicuous central constriction.

Chelifore scape of one article, relatively flaccid, chela small, functional. Palp 10-articled, as that of female, but with small gland-like swelling at mid-length of article 5. Oviger ( Fig. 1 B) 10-articled, as that of female, but article 7 proportionately longer, 1.35 times as long as article 6.

First leg ( Fig. 1 C) much longer than more-posterior legs, glabrous; first and third coxae subequal, second coxa 1.5 times as long as first coxa; femur four times as long as third coxa, without cement gland pores; tibiae subequal, just shorter than femur; tarsus three times as long as third coxa; propodus 0.6 times as long as tarsus, without main or accessory claws. Second, third ( Fig. 1 D) and fourth legs all similar, similar to those of female, femora with single row of 12 to 14 cement gland pores on slightly raised cones.

Measurements of male (mm). Length (anterior of cephalon to posterior of fourth lateral processes) 5.13; width across second lateral processes 3.8; proboscis (dorsal) 3.7; abdomen 1.95. First leg, first coxa 0.94, second coxa 1.5, third coxa 1.06, femur 4.25, first tibia 4.19, second tibia 4.13, tarsus 3.06, propodus 1.88. Third leg, first coxa 0.69, second coxa 1.19, third coxa 0.38, femur 3.06, first tibia 2.38, second tibia 1.88, tarsus 0.63, propodus 0.69, main claw 0.38.

Remarks. The only previous record of Ascorhynchus constrictus was that of the female holotype of Stock (1997), collected at 799–850 m depth off Vanuatu; that specimen lacked the distal articles of the first pair of walking legs. The discovery of this male, with a complete left first leg has allowed the completion of the description of the species, as well as the description of sexual dimorphism.

The male from Solomon Island is broadly similar to the female holotype, but bears conspicuous mid-dorsal setae on trunk segments 1 to 3; it is possible that these were detached in the holotype. Sexual dimorphism is shown by the presence of cement-gland pores in the femora of the posterior three pairs of legs, while the oviger is almost identical to that of the female, the seventh article being proportionately slightly longer.

The legs of the first pair were incomplete on the holotype but the left front leg is entire on the present specimen. While the second, third and fourth legs are basically identical in morphology, the first legs ( Fig. 1 C, drawn to the same scale as Fig. 1 D) are quite distinct, being 1.8 times as long as the third leg (stretched out), with a tarsus three-quarters as long as the second tibia, and without a main (or accessory) claws. The femur of the first leg is without cement-gland pores.

Dimorphism of the legs is shown in a number of Ascorhynchus species: in those species with a one-article chelifore scape, the “longitarsal” group (tarsus more than half as long as propodus) includes A. bacescui Stock, 1975 , A. ovicoxa Stock, 1975 A. utinomii Nakamura & Child, 1982 , A. diethius Child, 2002 , A glaberrimus Schimkewitsch, 1913 , A. minutus Hoek, 1881 and A. auchenicus ( Slater, 1879) with a reduced or “tiny” claw on the first legs, but only A. ramipes ( Bohm, 1879) and the present species share extremely long first legs lacking a claw (see Child, 2002). A. ramipes is easily distinguished from A. constrictus in having low, rounded dorsodistal tubercles on the lateral processes, low tubercles above the chelifore insertion and in the dorsal trunk midline, and two tubercles on coxa 1 or the legs, inter alia.

Figures

FIGURE 1. Ascorhynchus constrictus, male: A, trunk, dorsal, with first coxae of right legs; B, oviger; C, first leg; D, third leg, with detail of cement-gland pore. Scale line = 2 mm for A, 1 mm for B, 4 mm for C, D.