Anoplodactylus concavicollis Arango, 2003, new species

Anoplodactylus concavicollis new species

(figure 9)

Type material. Holotype X, GBR, Orpheus Island, Pioneer Bay, reef flat, in Galaxaura rugosa (Ellis and Solander), 27 July 1998. Two paratypes X, juvenile, same locality as holotype.

Other material. Same locality as holotype, 24 November 1998, five W, 17 X; 14 April 2000 one X. Great Palm Island, Cannon Bay, reef flat 2 m, in Laurencia sp. and G. rugosa, 28 November 1998, one W. Picnic Bay, intertidal, found in Laurencia sp. attached to rock, 3 October 1998, one W with eggs, one X. Turtle Bay, intertidal in C. prolifera, 27 March 1997, three W, four X, three juveniles (coll. Otto); 12 July 1999, one W; 4 May 2000, two W, two X; 1 July 2000, one X.

Diagnosis. One of the tiniest pycnogonids, leg span 2.5 mm, sides of the neck concave.

Description. Trunk length 0.64 mm, width 0.49 mm; ovoid in dorsal outline, glabrous, neck short, with concave sides, anterior pair of crurigers extends slightly forward beyond the oviger bases. Crurigers crowded together, armed with low rounded distal tubercles, ocular tubercle moderately tall, with large well-pigmented eyes and a low apical cone; abdomen typical (length 0.2 mm), erect, as tall as the ocular tubercle. Proboscis short, cylindrical, slightly tapering distally, carrying the mouth horizontally (length 0.3 mm). Chelifore scape one-segmented, glabrous, chelifores touching each other. Ovigers with six segments, third segment longest, last segment pointed, twice as long as wide. Legs short, with swellings, second coxae of fourth pair of legs with ventral genital spurs in males, a spine distally in femur and tibiae, cement gland a mid-dorsal tube. Females with swollen femora and smoother appearance, with same pattern of spination as males, propodus large, curved, strong heel, two heel spines, main claw more than three-quarters the length of the propodus, no auxiliary claws visible (total length third leg= 1.95 mm; 0.1–0.25–0.1–0.4–0.3–0.2–0.1–0.3–0.2).

Etymology. A compound name that refers to the unusually concave sides of the neck (Latin collis meaning neck) seen in dorsal view.

Distribution. This species is only known from localities near Townsville and coral reefs in the central section of the GBR.

Remarks. Anoplodactylus concavicollis is one of the tiniest sea spiders known. Given its relatively wide distribution in the area studied, it is expected the species had been overlooked previously due to its small size. The species is similar to A. viridintestinalis Cole, 1904 and also A. crassus Child, 1988. These share the ovoid trunk and small robust appearance with crowded crurigers, short proboscis and short legs but the characteristic shape of the neck is not found in any other species. Specimens from Picnic Bay Magnetic Island had a more greenish coloration.