Rhombognathides Viets, 1927

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 : 227-228

Rhombognathides Viets, 1927

(Fig. 68)

Type species. Aletes pascens Lohmann, 1889 .

Adults. Both female and male with genitoanal plate. Genital opening of female close to, that of male slightly removed from posterior margin of GP. Genital acetabula internal, three pairs present, in female posterior pair largest in size; anterior-most pair adjacent to or fused with middle pair of acetabula (Fig. 68). Female GA with three pairs of slender pgs; genital sclerites large, in ventral aspect often concealing anal plates; sgs lacking. Ovipositor short, at rest not extending beyond GO. Genital spines slender, hardly sclerotized. Ovipositor with four pairs of spines ( Trouessart 1894: pl. 10, 3b, b'; Bartsch 1975a: fig. 12b). Male GO slightly smaller than female GO; genital sclerites weakly delimited, not as operculiform as in female. GO surrounded by about 15–40 pairs of pgs; pgs slender and setiform or short, rather bristle-like, in some species (e.g. R. pascens ) posterior pairs of setae short and flattened ( Bartsch 1972: fig. 6). Genital sclerites with three pairs of short seti- to spur-like sgs. Three pairs of gac situated adjacent in posterior half of GO ( Newell 1947: fig. 26; Bartsch 1972: fig 7, 9, 11c, 2003c: fig. 9I). Acetabula slightly unequal in size. Adults without epimeral pores.

Juveniles. With one larva and two nymphs. In proto- and deutonymph genital and anal plate fused. GA of deutonymph with two pairs of internal gac, two pairs of pgs but no sgs ( Bartsch 2003c: fig. 9G). GA of protonymph with a pair of internal acetabula; pgs and sgs lacking. In contrast to nymphs AE of larva with epimeral pores.

Remarks. According to Bartsch (2009a) there are six valid species. Rhombognathides is spread in the northern Atlantic and Arctic Sea where it is commonly found amongst shallow water algae, often it is present in dense populations.