Halacarus werthi Lohmann 1907

Halacarus werthi Lohmann, 1907

Halacarus werthi: Lohmann (1907: 384–385, textfig. 11, 1–7); Newell (1984: 59–60, figs 114, 115).

Diagnosis. Length of female 653–750 µm, of male 620–740 µm. Anterior margin of AD cuculliform or slightly pointed; frontal protruding (spine) short, equalling 0.2 and less that 0.1 times that of AD and idiosoma, respectively. According to Newell (1984), posterior part of AD short, triangular; about same distance from level of glp-1 to both anterior and posterior margin of AD (glp-1 at 0.5), according to Lohmann (1907) posterior part much longer, linguiform. Ocular plates ovate; with cornea and canaliculus. Pair of ds-1 posterior to level of glp-1, situated about halfway between glp-1 and posterior margin of AD. Pairs of ds-5 and ds-6 anteromedial to glp-4 and glp-5, respectively, and distinctly distanced. PE with two dorsal and three ventral setae. Anterior margin of female GA broadly arched. Interval between anterior margins of GO and GA same as that between anterior margin of GO and end of anus.

Basal seta on P-2 at 0.4. Integument of legs punctate. Trochanters I to IV with 1, 1, 3, 1 setae. Both ventromedial setae on tibia II bipectinate. Tarsi I to IV with 2, 1, 1, 1 ventral setae, tarsi III and IV with four and three dorsal setae. Paired claws slender, with accessory process but without pecten.

Remarks. Unique in this species is that each PE bears two dorsal setae, moreover, the anterior margin of the AD is cuculliform. Lohmann (1907) presented a short description with two text figures, Newell (1984) a redescription on the basis of a single individual from Kerguelen. Differences in the descriptions regarding the length of the posterior part of the AD may be the result of differences in interpretation. Most Halacarus species have internal scars from muscle attachments in the posterior part of the AD and the adjacent striated integument, these scars may obscure the outline of the AD.

Distribution and ecology. Kerguelen. Taken amongst shallow water algae and polychaete tubes.