Rhopalorhynchus Wood-Mason, 1873

Takahashi, Yoshie, Dick, Matthew H. & Mawatari, Shunsuke F., 2007, Sea spiders (Arthropoda: Pycnogonida) from waters adjacent to the Nansei Islands of Japan, Journal of Natural History 41 (1 - 4), pp. 61-79 : 67

Rhopalorhynchus Wood-Mason, 1873

Diagnosis. Trunk extremely attenuate, fully segmented; lateral processes widely spaced; abdomen minute, more or less ventral in position; proboscis very slender, spindle-shaped, with a narrow, stalk-like basal part, with single tiny tooth mid-dorsally on inflated part; chelifores lacking; palps slender, 10-segmented with very tiny second segment; oviger in both sexes, slender, 10-segmented, strigilis with rows of spatulate spines often with serrate margin, single large distal spine on tenth segment, with terminal claw; legs slender, with sparse tiny setae; femur inflated distally; tarsus and propodus cylindrical, mostly straight, without spines; auxiliary claws lacking. Cement glands unknown.

Remarks. The genus Rhopalorhynchus differs from most other pycnogonids in the attenuated body, the spindle-shaped proboscis with dorsal tooth and with elongated stalk, and absence of both chelifores and palps. This genus includes 11 known species.

In general, Rhopalorhynchus species inhabit shallow tropical waters, whereas Hedgpethia species occur in temperate to cool waters. Species of Rhopalorhynchus inhabit the Indian Ocean, from South Africa and the Red Sea to western Australia, and also the western Pacific Ocean, from the Philippines to southeast of Australia. Rhopalorhynchus claudus Stock, 1975 from Barbados, western Atlantic Ocean, is distributed disjunctly from the rest of the genus. We further discuss distributional differences between Hedgpethia and Rhopalorhynchus in Remarks for Hedgpethia .