Rhopalorhynchus tenuissimum Haswell, 1884

Arango, Claudia P., 2003, Sea spiders (Pycnogonida, Arthropoda) from the Great Barrier Reef, Australia: new species, new records and ecological annotations, Journal of Natural History 37 (22), pp. 2723-2772 : 2737-2739

Rhopalorhynchus tenuissimum Haswell, 1884

(figure 6)

Colossendeis tenuissima Haswell, 1884: 1029–1030 , pl. 56, 5–8.

Rhopalorhynchus tenuissimus: Flynn, 1919a: 71–72 , pl. 53, 1–3.

Rhopalorhynchus tenuissimum: Stock, 1958: 114 (table), 117 (key); Staples, 1982: 465, figure 5A–J.

Material examined. Geoffrey Bay, 21 July 1982, one W (coll. J. Collins).

Description. Trunk length 2.10 mm, width 0.52 mm, fully segmented, very elongate form, completely glabrous, smooth cuticle, second and third segments longer than first and fourth, crurigers short, constricted at the base, separated by 10 times their diameter except third and fourth pairs that are much closer. Ocular tubercle at mid-point on cephalon, swollen distally, with pointed conical apex, small eyes, not dark-pigmented. Abdomen very reduced, horizontal, anus seen ventrally. Proboscis very long, anterior portion a long, thin peduncle, distal portion inflated, with a dorsal tooth on the anterior half. Palps 10-segmented, third segment longest, sixth to tenth segment similarly short. Fifth and third segments of the ovigers very long and slender, wider at the distal end, two rows of large pointed spines in the distal segments (strigilis). Legs long, slender, all segments glabrous except for short setae on coxae, femur and first tibia subequal, with distal swelling, tarsus, propodus and claw make 100% of the length of the second tibia, propodus straight, unarmed, claw about two-thirds of propodus.

Distribution. Rhopalorhynchus tenuissimum was described from a single specimen collected at Port Denison, Western Australia. There are unreported records at the Museum of Victoria of the species being found at Lady Julia Percy Island, Victoria and it has been found in South Queensland (Staples, 1982).

Remarks. Species of this genus with a toothed proboscis can only be differentiated by subtle variations of a few characters. Rhopalorhynchus tenuissimum was segregated from closely related R. kröyeri Wood-Mason, 1873 by the more anterior position of the dorsal tooth in the proboscis according to Stock’s key (Stock, 1958).