Brief review of the genus Apiosoma Blanchard, 1885 (Ciliophora: Peritrichia: Epistylididae)

The ciliates of the genus Apiosoma are important ectoparasites of fish. However, there is little information about the distribution, morphology, host specificity, and pathogenic potential of these unicellular microeukaryotes. Most studies on these parasites have been conducted in the former Union of Soviet Socialist Republics (USSR), and much of the literature is available only in local languages, which limits the dissemination and accessibility of information on the genus. In recent years, there has been an expansion of studies on the group, given its veterinary importance, as in high density they can cause respiratory problems, anorexia and difficulties in swimming to their hosts. However, most of these studies do not identify these ciliates at the species level, which may be problematic because responses to treatment can vary among ciliate species. To facilitate and encourage further research on Apiosoma, we compiled a checklist of 64 species reported worldwide, including information on their host associations and geographic distributions. In addition, to support species-level identification, we provide the main morphological characteristics for 56 of the 64 species included in the checklist.