A new species of Hedgpethia (Arthropoda, Pycnogonida, Colossendeidae) from southwestern Japan

Abstract We describe Hedgpethia spinosa sp. n. based on a single male specimen obtained from 197–207 m depth, south of Yaku Island, Kagoshima Prefecture, Japan. Among 15 previously known congeners, the new species resembles Hedgpethia bicornis (Losina-Losinsky & Turpaeva, 1958), Hedgpethia chitinosa (Hilton, 1943), and probably Hedgpethia brevitarsis (Losina-Losinsky & Turpaeva, 1958), in having a mid-dorsal tubercle on the posterior rim on each trunk segment. The new species, however, is distinguishable from those by a pair of horns on the anterior margin of the cephalic segment, spines on the first coxae, and denticulate spines on the strigilis. The new species represents the fifth member of the genus so far known from Japanese waters, in addition to Hedgpethia brevitarsis (Losina-Losinsky & Turpaeva, 1958), Hedgpethia chitinosa (Hilton, 1943), Hedgpethia dofleini (Loman, 1911), and Hedgpethia elongata Takahashi, Dick & Mawatari, 2007.

During a research cruise of the Training and Research Vessel Toyoshio-maru, Hiroshima University, in May 2005, a specimen of Hedgpethia was procured. We describe it as a new species in this paper.

Material and methods
Collection, preparation, and measurements of the specimens primarily follow the methods of Takahashi et al. (2007). The voucher specimen has been deposited in the Hokkaido University Museum, Sapporo, Japan (ZIHU). Description. Size small for genus, leg span only 6.5 mm. Trunk (Fig. 1A, 1B) moderately short for genus, completely segmented, posterior rims of segments 1-3 inflated, each with pointed dorsal median tubercle. Lateral processes almost as long as their basal width, separated from one another by slightly more than their basal width, glabrous. Cephalic segment with pair of horn-like spines at anterior margin. Ocular tubercle dome shaped, 1.5 times as high as its basal width, with pointed apex projecting slightly forward. Eyes slightly pigmented, anterior pair larger than posterior pair. Proboscis (Fig. 1A, 1B) 1.2 times as long as trunk, swollen, spindle shaped, constricted at middle of total length, slightly curved downward, tapering distally; lips rounded, each with short ciliary sheet. Abdomen very small, located on ventral side. Palps (Fig. 1C) longer than proboscis, slender; 10-segmented, with two short basal segments; first segment about twice as wide as other segments; second segment shortest; third segment longest, straight, with sparse, short setae, and with a few longer setae dorsodistally; fourth segment same length as sixth; fifth segment 0.6 times as long as third, with sparse setae over entire surface of distal half; seventh, eighth, and ninth segments subequal to sixth segment in length and slightly shorter than terminal segment; distal five segments fairly setose ventrally, setae as long as segment width, each segment with single short dorsodistal seta.

Hedgpethia spinosa
Oviger (Fig. 1D1) slender, long, 10-segmented; fourth and sixth segments longest, with very tiny setae ectally; fifth segment almost as long as second and third combined; strigilis (Fig. 1D2) armed with single short seta ectodistally, with rows of slender endal spines having denticles (Fig. 1D3); seventh segment equal to fifth in length; terminal segment less than two-thirds length and width of seventh segment; terminal claw short, about one-fifth as long as terminal segment, having small spines endally (Fig. 1D4).
Legs (Fig. 1E) slender, with many tiny setae over entire surface; first coxa with one small spine dorsally, one or two spines anteriorly and posteriorly, respectively; first and third coxae subequal and shorter than second coxa; femur almost equal to second tibia in length, curved ventrally, thickened in distal half, with several longer setae on distal end; tibia straight, with single long seta on distal end; first tibia 1.3 times as long as femur; tarsus slightly longer than propodus, both segments with dense, short setae ventrally and sparse, short setae dorsally; main claw about two-thirds as long as propodus.
Etymology. The specific name, a Latin adjective, refers to the spines on first coxae, anterior trunk margin, and terminal claw of oviger.
Remarks. Three species of Hedgpethia have pointed dorsomedian tubercles: H. bicornis (Losina-Losinsky & Turpaeva, 1958), H. chitinosa (Hilton, 1943), and probably H. brevitarsis (Losina-Losinsky & Turpaeva, 1958), the tubercles of which are slightly rounded. However, none of these has a pair of horns on the anterior margin of the cephalic segment, spines on the first coxae, or denticulate spines on the strigilis. The anterior spines of the cephalic segment have the appearance of vestiges of chelifores. This is one of the smallest species in the genus.