Halacarellus Viets 1927

Halacarellus Viets, 1927

(Figs 44–46)

Type species. Halacarus balticus Lohmann, 1889.

Adults. Female and male with GA. Female GA with two to four (rarely seven) pairs of pgs, genital sclerites with zero to five pairs of sgs. Three pairs of internal acetabula always distinct, in freshwater inhabiting species enlarged (Viets 1928a: fig. 49; Bartsch & Gerecke 2011: fig. 1H). Acetabula arranged in line along genital slit, anterior pair anterior or posterior to level of mid-GO (Fig. 44; Otto 1994: fig. 27). Ovipositor at rest often extending beyond GO. Ovipositor with two basal and eight or ten apical genital spines. Basal pair of genital spines papilli- or setiform. Apical genital spines dissimilar in shape, robust and with tines, slender and spiniform, or reduced to small papillae (Figs 45, 46; Womersley 1937: pl. 6, fig. 12; Bartsch 1998b: figs 31, 61, 2007b: fig. 6G). Male GA with 10–50 pairs of pgs and in general five pairs of sgs (rarely less). In the majority of species all three pairs of acetabula internal, arranged along genital slit; in a few species (of the H. capuzinus group) three pairs of acetabula arranged in posterior part of GO, within a fovea that opens to the exterior (Bartsch 1998b: fig. 48). In freshwater species two pairs of gac posterior to GO, enlarged and external, one pair of gac small, near middle of GO (Viets 1928a: fig. 48; Bartsch 1998b: fig. 15). AE without epimeral pores.

Juveniles. With larva and two nymphal stages. Nymphs of northern hemisphere species with genital and anal plate fused to a GA (e.g. in the type species H. balticus), most southern hemisphere species with GP and AP separated. Deutonymphal GA with two pairs of pgs, zero to two pairs of sgs and two pairs of gac (Newell 1951: figs 3, 19; Bartsch 1972: figs 25B, 28B, 1995a: fig. 19, 1998b: figs 24, 41, 63, 82, 101, 1990c: fig. 137, 1999c: fig. 3F). Acetabula of nymphs small and internal, large and internal or large and external (e.g. in H. hyrcanus (Viets, 1928) and H. fontinalis Bartsch & Gerecke 2011 (Bartsch 1998b: fig. 24; Bartsch & Gerecke 2011: fig. 2G). Protonymphal GA generally with pair of internal gac; pgs and sgs lacking (Bartsch 1972: figs 25D, 28F, 1995a: fig. 11, 1998b: figs 44, 85, 1999c: fig. 3G). Larva with pair of epimeral pores on AE (Bartsch & Panesar 2000: fig. 3). Larval anal plate often with large ventral part (Bartsch 1972: fig. 25F, 1998b: figs 67, 88).

Remarks. The genus, with about 50 species, is spread world-wide (Bartsch 2009a). Several of the species can be assigned to distinct species groups (Bartsch 1997a). Representatives of the northern Atlantic Ocean groups are not found on the southern hemisphere and vice versa (Bartsch 1997a).