Phacacarus Bartsch, 1992 (Fig. 67) Type species. Phacacarus flavellus Bartsch, 1992. Adults. Genital and anal plate fused in both female and male. Female with two pairs of pgs; sgs lacking (Bartsch 1992c: fig. 2). With single pair of gac, situated in about middle of GO (Fig. 67). Ovipositor very short, at rest not extending beyond GO. Genital spines small, their number and shape not known. Male GA with two pairs of slender pgs; GO large, sgs absent (Bartsch 1994a: fig. 2). AE with pair of epimeral pores. Juveniles. At present only larval but no nymphal stage found. AE of larva with pair of epimeral pores. Remarks. A single species is known which has been collected on the western coast of Australia Bartsch (1992c). Phacacarus flavellus is expected to have a special mode of living. At present known are the female, male and larva but no nymphs. The species has several unusual characters. The females have large, solid, pigmented dorsal and ventral plates, the legs bear large lamellae. The males have very delicate, unpigmented plates and their legs lack the wide lamellae. The larva has an unusual minute PD, it is just a sclerite surrounding the posterior pair of gland pores. In contrast to most halacarid species, Phacacarus has an unusual short gnathosoma and rostrum but solid chelicerae and a large pharyngeal plate that extends posteriad far beyond the gnathosoma. In the related genus Copidognathus, the shape of the legs is almost the same in female and male, there is no striking difference in the pigmentation, thickness and shape of the dorsal plates, and the posterior dorsal plate of the larvae is smaller than in adults but never as miniaturized as in Phacarus larvae. In both genera the legs of the larvae never have such wide lamellae as present in females. Phacacarus flavellus was found amongst coralline algae, more details are not known. Because of the reduced and delicate plates, the males and larvae are expected not to live on and amongst the algae, as assumedly the females do, but more or less inside a cavity, perhaps in the coralline algae, gnawed with those solid chelicera. Though speculative, the nymphal instar(s) may have been reduced in the course of this life-style.

Published as part of Bartsch, Ilse, 2015, The genital area of Halacaridae (Acari), life stages and development of morphological characters and implication on the classification, pp. 201-259 in Zootaxa 3919 (2) on page 226, DOI: 10.11646/zootaxa.3919.2.1, http://zenodo.org/record/245246