UNIONICOLINAE Oudemans, 1909

Gledhill, Terence & Vidrine, Malcolm F., 2002, Two new sympatric water-mites (Acari: Hydrachnidia: Unionicolidae) from the mutelid bivalve Aspatharia sinuata (von Martens) in Nigeria with some data on unionicoline-bivalve relationships, Journal of Natural History 36 (11), pp. 1351-1381 : 1354-1355

Subfamily UNIONICOLINAE Oudemans, 1909 Genus Unionicola Haldeman, 1842 Subgenus Mutelicola new subgenus

Diagnosis. With the characters of the genus. Idiosoma length 500–1000. General body form similar to species of the subgenera Australatax Vidrine, 1985 , and Unionicolides Lundblad, 1937 . Dorsal shield, which may be indistinct or absent in females of some species, and epimera resemble those found in Australian species of Australatax . Female genital eld with four (two each side) acetabula-bearing plates resembling those displayed by females in Australatax . However, six or more pairs of acetabula are present in Mutelicola and only ve pairs in Australatax . Male genital eld with four (two each side) heavily sclerotized acetabula-bearing plates, ve or more pairs of prominent acetabula and with a more-or-less central pair of somewhat thickened, elongate setae on each side of the gonopore. These setae, which may be separate or arise from a common base, are similar to, but diOEerent from, those of males in Crowellatax from New Zealand, the only other subgenus in which males have thickened setae in the central region of the genital eld. However, Crowellatax has only two acetabula plates and ve pairs of acetabula and the setae are positioned anterior to the centre of the genital eld. Additionally, the acetabular plates and acetabula of Crowellatax , unlike those of Mutelicola, are only lightly sclerotized and the subgenus, with only one known species, is recorded from sponges. Male and female legs similar. Enlarged, curved distal setae present or absent on IV-Leg segments. All legs with a pair of elongate, somewhat attened setae extending dorsally and distally over the claws. These setae resemble those found in species of the subgenera Australatax , Unionicolides and Atacella Lundblad, 1937 .

The uniqueness of the male genital eld is su cient in the current taxonomy of Unionicola s. l. to warrant separation from existing subgenera. Other characters, taken as a group, serve not only to isolate Mutelicola morphologically, but also link it to existing subgeneric groups. Palp and leg morphology clearly ally Mutelicola with Australatax and Unionicolides and their cluster of subgenera including Kovietsatax , Unionicolella , Atacella and Berezatax ( Vidrine, 1996a) . For example, the somewhat attened setae extending dorsally and distally over the claws are common to all these subgenera. An obvious diOEerence where palps are used to distinguish subgenera within this group occurs in Atacella and Berezatax ; both possess obviously dorsoventrally- attened palps. Species with reduced chaetotaxy on palps and legs (presumably derived conditions) can be found in Berezatax , Unionicolella , Unionicolides , Atacella and Australatax , demonstrating obvious divergences within this group not yet found in Mutelicola. Australatax , Kovietsatax and some Atacella have elongated projections on the inner edges of the female genital plates; these are likewise apparent in Mutelicola which also has the greater number of genital acetabula; the most any of the close subgenera possess is six pairs. The enigmatic South American subgenus Polyatacides , also included in this group, has 10 pairs of acetabula but the male has only two genital plates and no obvious setae, the palps also have distinctly block-like segments. Mutelicola obviously extends the host range and geographic range of mussel-associating unionicoline mites. Thus the morphology and chaetotaxy of the palps, legs and genital eld, the morphology of the epimera, acetabula number, host range and geographic range, clearly distinguish Mutelicola from all other unionicoline subgenera.

Type species. Unionicola (Mutelicola) blayi new species.

Etymology. The subgenus name is formed from the mutelid bivalve family name Mutelidae and the su x cola used adjectivally and meaning ‘dwelling in’.