Halacarus actenos robustus: Viets (1950: 4–6, fig. 1 A–E). Halacarus falklandensis: Newell (1984: 56–57).
Diagnosis. Length of female 630–690 µm, of male 560 µm. Frontal spine moderately long, slender, equalling 0.3 times length of AD and less than 0.1 times length of idiosoma. Posterior part of AD linguiform. Pair of glp- 1 at 0.6. Pair of ds- 1 posterior to glp- 1, about halfway between glp- 1 and posterior margin of AD. Ocular plate ovate, with cornea and canaliculus in posterior margin. Pairs of ds- 5 and ds- 6 slightly anteromedial to level of glp- 4 and glp- 5, respectively; setae removed from gland pores by more than their diameter. Anterior margin of female GA broadly rounded; GA large, in small individuals extending almost to level of posterior edge of PE, in a large female far from that level. Interval between pgs- 1 and margin of GA equalling half the distance from anterior margin of GA to that of GO. The latter distance about twice length of GO. Anterior margin of male GA rounded; GO in middle of plate; distance from anterior margin of GA to GO almost same as distance from posterior margin of GO to end of anal sclerites. Male with 75 pgs around GO.
Gnathosoma about 2.0 times longer than wide. Rostrum slightly longer than gnathosomal base and reaching to end of P- 2. Basal seta on P- 2 at 0.6. Integument of legs punctate. Telofemur, genu and tibia I with 2, 2, 4 spiniform and tapering ventral setae. Basalmost ventral spine at 0.3–0.4. Tibiae I to IV each with four bristle-like ventral setae. On tibia II both ventromedial setae long and bipectinate; ventromedial seta on genu II similar-sized and bipectinate. Trochanters I to IV with 1, 1, 3, 1 setae, basifemora I to IV with 2, 4, 2, 2 setae. Tarsi I to IV with 2, 1, 1, 1 ventral setae. Tarsi III and IV with four and three dorsal setae, respectively. Paired claws of all tarsi with very delicate accessory process, without pecten.
Remarks. Halacarus falklandensis has similar-sized bipectinate setae on genu and tibia II and the female GA is long. Halacarus falklandensis shares characters with H. echinatus but has a shorter spine and shorter rostrum.
Bartsch (1979 b) mentioned two females of Halacarus robustus which had been taken off the Marion Island, Prince Edward Islands. These individuals may belong to H. falklandensis.
Distribution and ecology. Southern West Atlantic, Falkland Islands, amongst shallow water sand (22 m).