Halacarus prolongatus Bartsch, 1996

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

Halacarus prolongatus Bartsch, 1996

Halacarus prolongatus: Bartsch (1996: 162–165, figs 14–21) .

Diagnosis. Length of female 750 µm, of male 615–760 µm. Epicuticula of plates and legs delicately reticulate, that of striated integument maze-like. Frontal spine long and slender, its length half that of AD and almost 0.2 times that of idiosoma. Posterior part of AD spiniform. Pair of glp-1 at 0.7. Pair of ds-1 immediately anterior to level of glp- 1. Corneae and ocular plates absent. Canaliculi in striated integument. Pairs of ds-5 and ds-6 immediately adjacent to glp-4 and glp-5, respectively. Apodemes of PE extending to medial margin of plate. Pair of pgs- 1 in both female and male in striated integument slightly anterior to level of posterior edge of PE. In female distance between pgs-1 and widely arched anterior margin of GA 1.1 times that between margins of GA and GO. Male genital plate round; 72 pgs around GO and one pair of outlying pgs anterior to GA.

Gnathosoma about 2.6 times longer than wide. Rostrum longer than gnathosomal base and extending beyond end of P-2. Basal seta of P-2 at 0.7. Leg segments slender; legs I, III and IV longer than idiosoma. Trochanters I to IV with 1, 1, 2, 1 setae, basifemora I to IV with 2, 4, 2, 2 setae. Telofemur, genu and tibia I with 2, 2, 4 spiniform ventral setae. Basalmost ventral spine on telofemur I at 0.4. Ventromedial seta on genu II slender, smooth. Tibiae I to IV each with four bristle-like ventral setae, on tibia II one of setae bipectinate. Tarsi I to IV with 2, 4, (3–)4, (3–)4 large ventral setae, respectively. Tarsi III and IV with four and three dorsal setae, respectively. Paired claws with minute accessory process.

Remarks. This is one of the rather few species which lacks OC or corneae. Halacarus longiunguis shares this character with H. prolongatus but has much more slender claws, claws II to IV have no accessory process, a seta on P-2 is in a more basal position, the female GA is much larger and males have a higher number of pgs than present in the latter species.

Distribution and ecology. Mid-Atlantic Ridge, 37°51’N, 32°31’W and 37°51’N, 31°31’W, from 824–845 m depth (an unpublished record included). The records are from hydrothermal vent areas.