Halacarus robustus Lohmann, 1907

Bartsch, Ilse, 2011, Halacarus socius (Acari: Halacaridae), description of the male and diagnoses of species of the Halacarus actenos group, Zootaxa 2800, pp. 18-40 : 34-35

Halacarus robustus Lohmann, 1907

Halacarus actenus var. robusta: Lohmann (1907: 385, pl. 36, figs 1–7) . Halacarus robustus: Newell (1984: 57–59) .

Diagnosis. Length of female 850–900 µm ( Lohmann 1907), 731–809 µm ( Newell 1984), of male 653–705 µm ( Newell 1984). Frontal spine long, slender, extending almost to end of P-2. Length of spine almost half that of AD and 0.1–0.2 times that of idiosoma. Posterior part of AD linguiform, with truncate posterior margin ( Lohmann 1907) or short, triangular ( Newell 1984). Dorsum with five ( Newell 1984) to six ( Lohmann 1907) pairs of gland pores. Pair of glp-1 at 0.6 ( Lohmann 1907) to 0.7 ( Newell 1984). Pair of ds-1 well posterior to level of glp-1. OC small, ovate, with cornea and canaliculus. Pair of ds-5 distinctly anterior to glp-4. Pair of ds-6 immediately adjacent to glp-5 ( Newell 1984). Two pairs of pgs in striated integument in both female and male, anterior pair (pgs-1) level with end of PE, following pair of setae close to GA. Distance between pgs-1 and wide, rounded to straight anterior margin of female GA almost same ( Lohmann 1907) or twice ( Newell 1984) that between anterior margins of GA and GO. The latter distance equalling about length of GO. Anterior margin of male GA round, with 45–48 pgs on either side of GO. Distance from anterior margin of GA to GO more than length of GO.

Gnathosoma about 2.3 times longer than wide. Rostrum longer than gnathosomal base and extending to end of P-3. Basal seta on P-2 at 0.7. Epicuticula of legs delicately punctate. Trochanters I to IV with 1, 1, 2, 1 setae, basifemora I to IV with 2, 4, 2, 2 setae. Telofemur to tibia I with 2, 2, 4 smooth, tapering ventral spines. Ventral spine on telofemur I at 0.3–0.4. Ventromedial seta on genu II smooth, both these setae on tibia II bipectinate. According to Newell (1984), tarsi I to IV with 2, 2–4(?), 0, 0 bristle-like ventral setae, tarsi III and IV with four and three dorsal setae. Paired claws with accessory process but no tines.

Remarks. The description by Lohmann (1907: pl. 36, figs 1–7), though rather detailed, left several details unmentioned, Newell (1984) re-described the species on the basis of a female of the type series (from Kerguelen Islands) and specimens from off the Macquarie Island. The specimens mentioned by Bartsch (1979b), taken off the Marion Island, Prince Edward Islands, are much smaller and bear a single pair of pgs in the striated integument; the specimens are most similar to H. falklandensis .

Distribution and ecology. Southern Indian and adjacent Pacific Ocean (Kerguelen, off Macquarie Island). From shallow to 278 m water depth.