Halacarus Gosse, 1855

Bartsch, Ilse, 2015, The genital area of Halacaridae (Acari), life stages and development of morphological characters and implication on the classification, Zootaxa 3919 (2), pp. 201-259 : 219

Halacarus Gosse, 1855

(Figs 48 and 49)

Type species. Halacarus ctenopus Gosse, 1855 .

Adults. Genital and anal plates fused. Female GA often with cerotegumental layer close to GO. GA with (1–)2–15 pairs of slender pgs; species with (one or) two pairs of pgs often with third (rarely fourth) pair of pgs in striated integument anterior to GA. Genital sclerites with three to five pairs of small sgs. Genital acetabula often large, internal; three tube-like pairs present ( Newell 1947: figs 98, 129). Acetabula arranged adjacent or posterior pair separated from two anterior pairs (Fig. 48; Newell 1947: fig. 129; Bartsch 2010b: fig. 4). Ovipositor short, at rest only slightly extending beyond GO, when everted long, slender genital spines seen, namely two pairs of anterior and three pairs of posterior spines ( Trouessart 1894: pl. 10, fig. 2a, a'; Bartsch 2005a: fig. 20). Male GA with about 30 to more than 150 filiform pgs arranged around GO. Often one or more pairs of pgs outlying; anteriormost pair of pgs either on or anterior to GA. GO smaller than in female and in a more ventral position, somewhat removed from anal cone. Three pairs of gac often slightly shorter than in female, situated adjacent in posterior part of GO (Fig. 49; Newell 1947: figs 95, 128; Bartsch 2010b: figs 6, 7). Genital sclerites with three to five pairs of short sgs, three posterior pairs of setae generally spur-like. AE of adults without epimeral pores.

Juveniles. With larva, proto- and deutonymph. GP and AP in deutonymphs generally separated, rarely fused ( Bartsch 1981a: figs 24, 36, 56, 1993b: fig. 13K), GP often small. Deutonymph with two pairs of internal gac, two pairs of pgs, either both on GP, both in striated integument or one pair on GP and one in striated integument anterior to GP, and generally with a pair of sgs, rarely that pair absent ( Newell 1947: figs 92, 96, 115; Bartsch 1981a: figs 4, 24, 36; Pepato & Da Silveira 2013: fig. 2B). Protonymph with GP and AP separated; GP small, even almost absent; one pair of internal acetabula and a single pair of minute setae within GP or in striated integument, situated very close to acetabula ( Bartsch 1981a: fig. 6, 2002: fig. 46, 2007b: fig. 9G; Pepato & Da Silveira 2013: fig. 2H). Nymphs without, larva with pair of epimeral pores.

Remarks. The majority of the presently known 76 species ( Bartsch 2009a, 2011b; Pepato & Da Silveira 2013) are rather large-sized, the length of their idiosoma between 400 and 1500 µm. Records of the genus are from all oceans and depth zones from the waterline to deep-sea basins. Most of the species are epibionts on various substrata, only a few species are psammophilous.