The symbiotic water mite Unionicola formosa (Acari : Unionicolidae) ingests mucus and tissue of its molluscan host

Unionicola formosa is a symbiotic water mite that passes most of its life c ycle in the mantle cavity of freshwater mussels. Although mites of this gen us are often referred to as parasitic, little is known about their nutritio nal biology. A few species reportedly pierce the gill of a host mussel and ingest tissue or hemolymph. The present study was undertaken to identify po ssible sources of nutrition for U. formosa. To determine if mites ingested particulate matter in the mucous strand produced by a mussel during feeding , mussels with resident mites were exposed to a suspension of fluorescent m icrospheres. There was no evidence that U. formosa ingested the beads. Hist ochemical staining did, however, indicate a mucous material present in the midgut of the mites. Sodium dodecyl sulfate-polyacrylamide gel electrophore tic assays revealed a high molecular weight component, consistent with a mu copolysaccharide, present both in the mussel gill and the mites. Results fr om western blots and an immunoaffinity binding assay with antibodies agains t mussel gill tissue and hemolymph also indicated that mites ingested host tissue. Whereas U. formosa probably does not ingest particulate material ac quired by its host's suspension feeding, it is apparent that this mite util izes host mucus, gill tissue, or hemolymph for at least part of its nutriti on.