Halacarus socius Bartsch, 1992

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 : 35

Halacarus socius Bartsch, 1992

Halacarus socius: Bartsch (1992: 468–470, figs 8–15; present paper, figs 1–19) . Halacarus tritoni: Otto (2001: 710–712, figs 19A–D, 20A–E) .

Diagnosis. Length of female 407–520 µm, of male 348–405 µm. Surface of dorsal and ventral plates delicately reticulate. Frontal spine short, triangular (rarely spine absent), its length 0.1–0.2 times of that of AD and less than 0.1 times of that of idiosoma. Posterior part of AD wide, linguiform, posterior margin almost truncate. Pair of glp-1 at 0.5. Pair of ds-1 about level with glp-1. Corneae in striated integument. Pair of canaliculi in striated integument immediately posterior to cornea. Pairs of ds-5 and ds-6 medial to glp-4 and glp-5, respectively, and somewhat removed from pores. Anterior margin of female GA wide, rounded. Anterior pair of pgs in striated integument at level of end of PE and far anterior to GA; distance from pgs-1 to margin of GA 0.9–1.3 times that between anterior margins of GO and GA. Ovipositor anteriad slightly extending beyond GO. Male GA almost reaching level of posterior setae on PE. Pair of pgs- 1 in striated integument close to margin of GA, another 50–55 pgs around GO. Distance between anterior margin of GA and GO about same as length of GO.

Length of gnathosoma slightly more than twice the width (2.1–2.2 times). Rostrum longer than gnathosomal base, extending to end of P-3. Basal seta on P-2 at 0.7. P-3 with bluntly ending spine. Trochanters I to IV with 1, 1, 2, 1 setae. Basifemora I to IV with 2, 4, 2(–3), 2 setae. Telofemur to tibia I with 2, 2, 4 smooth, tapering ventral spines. Ventralmost spine on telofemur I at 0.5. Ventral seta on genu II much longer than slender and smooth ventromedial seta. Both ventromedial setae on tibia II bipectinate. Tarsi I to IV with 2, (2–)3(–4?), 4, 3(–4) bristle-like ventral setae, tarsi III and IV with four and three dorsal setae. Accessory process of paired claws with about seven tines.

Remarks. The species is characterized by its rather small frontal spine and having the ds-1 at about the level of the glp-1. In its general shape the species is similar to H. hemispinosus , H. higginsi , H. magniporus , and H. mollis , but H. hemispinosus has the ds-1 posterior to the level of glp-1, H. higginsi has a shorter gnathosoma and shorter female and male GA relative to the position of the pair of pgs-1, H. magniporus has smaller corneae and the ds-5 and ds-6 immediately adjacent to the glp-4 and glp-5. The description of H. mollis is fragmentary, but the gnathosoma seems to be shorter, relative to its width, and the distance between the anterior pair of pgs and the anterior margin of the male GA larger than in H. socius .

Distribution and ecology. Tropical western Pacific (Society Islands, Great Barrier Reef, Sulawesi) and Indian Ocean ( Mauritius, Sri Lanka). All present records are from shallow waters.