Halacarus flavellus Bartsch, 1993

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 : 28-29

Halacarus flavellus Bartsch, 1993

Halacarus flavellus: Bartsch (1993b : 53–56, figs 5A–F, 6A–E; 2007b: 374–376, fig. 7A–E).

Diagnosis. Length of female 531–720 µm, of male 473–565 µm. Frontal spine moderately long, often flattened, spatula-shaped; its length 0.4 and 0.1 times that of AD and idiosoma, respectively. Middle part of AD with parallel margins, posterior part triangular and with obtuse end. Pair of glp- 1 in striated integument, at 0.6 relative to length of AD. Pair of ds-1 on AD, posterior to level of glp-1. Ocular plate ovate, with cornea and canaliculus. Pairs of ds- 5 and ds-6 medial to glp-4 and glp-5, respectively, distinctly removed from gland pores. Anterior margin of female GA widely rounded, almost truncate. Pair of pgs-1 posterior to level of end of PE; its distance to anterior margin of GA equalling 0.8 times interval between margins of GA and GO; that distance in turn similar to length of GO. Male GA elongate. Anterior margin truncate and with pgs- 1 in its angles. GO surrounded by about 100 pgs.

Gnathosoma 2.1 times longer than wide. Rostrum longer than gnathosomal base; extending to end of P-2. Basal seta on P-2 at 0.9. Spine on P-3 slender, pointed. Epicuticula of leg segments delicately porose. Telofemur, genu and tibia I with 2, 2, 4 spiniform ventral setae. Basalmost ventral seta on telofemur I at 0.4. Trochanters I to IV with 1, 1, 2, 1 setae, basifemora I to IV with 2, 4, 2, 2 setae. Genu and tibia II with one and two long, bipectinate ventromedial setae, respectively. Tarsi I to IV with 2, 1, 1, 1 ventral setae; tarsi III and IV with four and three dorsal setae, respectively. Paired claws with large accessory process bearing a cluster of 15–20 tines.

Remarks. Halacarus flavellus is one of the few Halacarus species which has the pair of glp- 1 in the striated integument, outside the AD. A similar situation is found in e.g. H. frontiporus Newell, 1947 , H. celatus Bartsch, 1993 and H. validus Gimbel, 1919 . These species do not belong to the H. actenos group. Males of H. flavellus have the pgs- 1 in the anterior angles of the GA, in general these setae are situated anterior to the GA in the striated integument.

Distribution and ecology. Australia, Western Australia, Rottnest Island and Esperance. Abundant amongst the epiflora and fauna growing in sheltered bays on various shallow water substrata, algae, seagrass.