Ciliate (Protozoa) epibionts of deep-water asellote isopods (Crustacea): Pattern and diversity

Examination of 32 species from seven families of marine asellote isopods (Crustacea, Malacostraca) showed that 15 of these species were infested with ciliate epibionts. The diversity of the ciliate epibiosis was fairly high (mean = 3.8 epibiont ciliate species per host species; range 1 to 10 species). Ciliates were absent from species of the family Janiridae and were rare on desmosomatids. The prevalence was high (≥ 37%) on two ischnomesid species (Ischnomesus norvegicus and Heteromesus frigidus), and on three munnopsid species (genus Ilyarachna). Mean intensity was fairly low (1.3-10.5) overall, but high on I. norvegicus (29.2). Some ciliate species showed host preferences. Predatory ciliates (subclass Suctoria) were most common on host species of the families Munnidae and the Nannoniscidae and some of the Ischnomesidae species, whereas suspension-feeding ciliates (subclass Peritrichia) were found on six host species only, belonging to the family Ischnomesidae or the subfamily Ilyarachninae (Munnopsidae). Grooming, body texture of the isopods, and their burrowing or their use of pits and holes in the substrate may shape the pattern of ciliate epibiosis. Abrasion during burrowing or redox conditions found within the sediments may explain the absence or near absence of ciliates from Haploniscus bicuspis and the desmosomatids. By contrast, suspension- or detritus-feeding epibionts live on hosts which use shallow open pits or holes in the substrate (ilyarachnids, some ischnomesids).