Pycnogonum grumus, Arango, 2003

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 : 2763

Pycnogonum grumus new species

(figure 16)

Type material. Holotype X, Coral Sea, Holmes Reef, reef drop off, 18 m, in Amphiroa sp. , hydroids and sponges washing, 18 September 1998 (coll. Diaz-Pulido). Diagnosis. A dorsal rounded tubercle on proboscis and abdomen, a single median dorsal tubercle on first to third segments, two diverging tubercles on fourth. Description. Trunk 1.26 mm in length, width 0.58 mm, fully segmented, compact, segments with cowlings in which the posterior margin is raised over the next segment, cuticle granulate, three stout dorsomedian tubercles, smooth collar at base of proboscis, crurigers almost touching, the fourth pair smaller and pointing backwards, broad distal tubercle on each cruriger, those on last pair are larger. Ocular tubercle very low, rounded, anterior eyes not pigmented, granulate, abdomen horizontal, jointed from underneath last segment (length 0.3 mm), with dorsal tubercle; proboscis cylindrical, distally tapering, with a dorsal tubercle in the middle (length 0.4 mm). Legs short, robust, first pair somewhat longer, all coarsely granulated, dorsal row of coarse granules, femur not so densely granulated, single distal long spine on femur and tibiae, propodus as long as first tibia, without heel, robust main claw half the length of the propodus (total length third leg= 1.38 mm; 0.14–0.12–0.14–0.24–0.24–0.18–0.2–0.12).

Etymology. From the latin grumus meaning a small heap, the name refers to the dorsal protuberance on the proboscis and abdomen of this species of Pycnogonum .

Distribution. Only known from Holmes Reef in the Coral Sea.

Remarks. This specimen has similarities with P. asiaticum Müller, 1992 described from Malaysian coral reefs, in the shape of the trunk and pattern of tubercles in the dorsum but the new species does not have auxiliary claws and does not have the papillose pores covering the body. Pycnogonum saxulum Child, 1998 , another West Pacific reef species, resembles P. grumus in the lack of auxiliaries but it is more compact and the median tubercles are ‘pebbly’ in appearance (Child, 1998a). Although it is not satisfying to describe a species based on a single specimen (possibly a juvenile), the presence of a tubercle on the proboscis, another on the abdomen and the lack of auxiliaries do not allow me to fit the specimen in any of the known species of Pycnogonum .