Ascorhynchus heuresis, Bamber, 2002

Bamber, Roger N., 2002, Bathypelagic pycnogonids (Arthropoda, Pycnogonida) from the Discovery deep-sea cruises, Journal of Natural History 36 (6), pp. 715-727 : 716-718

Ascorhynchus heuresis sp. nov. (®gure 1)

Material. One male (holotype), Station 10379#38, 35ss57.0¾N 32ss53.3¾W, 2840± 2980 m, 14 June 1981 (Registration No. NHM 2000.26 6).

Description of male. Relatively small species. Trunk (®gure 1A±C) fully segmented, glabrous, ®rst three segment posteriors slightly raised and bearing pointed mediodorsal tubercle; lateral processes separated by just less than their own diameters, each bearing pointed dorsodistal tubercle. Cephalon with pair of pointed anterodorsal tubercles (`horns’); ocular tubercle at anterior margin, pointed, with four eyes. Last trunk segment without dorsal tubercle. Abdomen slender, naked, horizontal, extending to less than half length of coxa 2 of leg 4.

Chelifore scape of single article, cylindrical, curved, naked; chela digitate, tiny, movable ®nger ināted proximally, ®ngers distally very slender.

Palp (®gure 1E) of 10 articles, article 3 naked, longer than 5, article 5 ināted, distal articles not very slender, with few ventral setae.

Oviger (®gure 1A) of 10 articles, proximal three short, 5>4>6, strigilis articles subequal, bearing 5, 4, 4 and 4 compound spines, respectively, distal claw slender, pointed, not denticulate, shorter than distal article.

Legs (®gure 1D) slender; coxae 1 and 3 subequal, half length of coxa 2; femur with few setae, single dorsal cement gland pore just distal of median; tibia 1 longer than femur, dorsal, lateral and ventral setae, some as long as tibial diameter; tibia 2 longest article, setose as tibia 1 plus group of short`sole’ setae distally; tarsus slender, with nine short sole setae; propodus 1.5 times tarsus, with nine short sole setae, elongate dorsal seta. Main claw stout, half length of propodus. Auxiliary claws absent.

Female unknown.

Measurements (mm). Trunk length (anterior edge of cephalon to base of abdomen) 2.23; width across second lateral processes 1.32; proboscis 1.6; abdomen 0.73; leg 2, coxa 1 0.35; coxa 2 0.67; coxa 3 0.3; femur 2.27; tibia 1 2.73; tibia 2 2.93; tarsus 0.41; propodus 0.59; main claw 0.28.

Etymology. From the Greek (as consistent with the generic name) for a discovery (noun, gender female), after the survey vessel.

Remarks. There are 10 described species of Ascorhynchus with a single-articled chelifore, tarsus greater than 50% of the propodal length (`longitarsal’), and with tubercles mid-dorsally on the trunk, distally on the lateral processes and anterodorsally on the cephalon (`horns ’). Of these, the new species shows similarities, particularly in the swollen ®fth palp article and the non-tripartite proboscis, inter alia, to Ascorhynchus simplex Nakamura and Child, 1991 from Sagami Bay, Japan (at 110±122 m depth) and A. orthostomum Child, 1998 from New Zealand waters (1400±1586 m).

Proportions of the articles of the ovigers and legs of these three species are very similar. They are most evidently distinguished by the number of cement gland pores, Ascorhynchus simplex having eight to nine per femur, A. orthostomum having two, and the present species only one. The proboscis of Ascorhynchus simplex is nearly as long as the trunk, that of A. orthostomum is longer than the trunk, and both are cylindrical distal to the peduncular area; the proboscis of A. heuresis sp. nov. is about 70% of the trunk length and bulbous. The abdomen of the new species extends to less than half the length of coxa 2 of leg 4, while those of the other two species extend to the distal edge of coxa 2. Also, while the distal palp articles of the other two species are`very slender’ (some four times as long as wide), those of the new species are less then three times as long as wide. Ascorhynchus heuresis sp. nov. is the least hirsute, notably on the proximal articles of the palp and oviger.

The specimen was collected from an epibenthic trawl on the eastern slope of the Mid-Atlanti c Ridge.