Achelia nana Loman, 1908

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 : 2730

Achelia nana Loman, 1908

Ammothea nana Loman, 1908: 60–61 , pl. 1, figures 1–13.

Achelia nana: Stock, 1953a: 300–301 , figure 14; 1954: 97; 1965: 14–15, figures 1–3; Child, 1983: 699.

Material examined. Holmes Reef, 18 m, collected by scuba in fouled rubble with hydroids, sponges and algae, mainly Amphiroa sp. , 17 September 1998, one X (coll. Diaz-Pulido).

Description. Trunk length 0.64 mm, width 0.52 mm, third segmentation line not distinct, two antero-dorsal tubercles at each side of the cephalic segment; crurigers crowded, with a distal tubercle each; ocular tubercle low; abdomen strongly inclined to the front. Proboscis inflated at mid-point in an elliptical shape, typical of the genus. Palps eight-segmented, distal segments with ventral projections and long setae. Fifth segment of the ovigers the longest, formula 1:1:1:2, tenth segment less than half the size of the ninth. Femur the longest segment of legs, with dorso-distal spur tipped with a spine, first tibia shorter than second, single posterior tubercle and two smaller in the anterior margin of first coxa, second coxa with two tubular spines, two heel spines in propodus, claw half the length of the propodus, auxiliaries about three-quarters of the claw.

Distribution. This is the first record of the species from Australian waters. It is a common shallow-water species found from the shore to 30 m at different locations from Madagascar to Japan through the Indo-west Pacific to New Caledonia. This record of A. nana from an offshore reef in the Coral Sea extends the distribution to Australian waters, however the species has not been recorded along the coast.

Remarks. This is a species of the so-called echinata -group of the genus Achelia (Stock, 1954) , characterized by the spiny legs and the proboscis inflated at the middle. This specimen fits the description of A. nana illustrated by Stock (1965), in the pattern of spines on the legs and ovigers. According to Child (1988a), A. nana might have been replaced by A. variabilis Stock, 1954 in Australian and New Zealand waters where A. nana had not been collected before. This specimen is not identified as A. variabilis because of the smaller size of this adult female compared to the average measurements given by Stock and differences in arrangements of spines of second coxae. Bearing in mind the difficulties in the taxonomy of the genus and the lack of sufficient material to justify the validity of one species or the other, this classification of species of Achelia should be regarded as tentative until systematic and phylogeographical analyses of the genus are carried out.