Ecological Studies on the Associations of Chitons in Puerto Rico, with Special Reference to Sphaeromid Isopods

Five symbiotic isopod-chiton relationships are described, viz., Dynamenella perforata with Acanthopleura granulata and Chiton tuberculatus, Exosphaeroma (a) with C. tuberculatus, Exosphaeroma (b) with C. marmoratus, and Dynamenopsis dianae with C. tuberculatus. The inhalant chamber of the pallial groove was the site most often frequented by the isopods. Other chiton symbionts described are “Acervulina inhaerens” (Foraminiferida), Harpacticus sp. and Heterolaophonte (Harpacticoida), Parhyale hawaiensis (Amphipoda), and Actaletes neptuni (Collembola). Dynamene moorei is shown to be conspecific with Dynamenella perforata. A widespread occurrence of the Dynamenella-Acanthopleura partnership is indicated by records from Jamaica, Cuba, Florida, the Bahama Islands, and Barbados. It is shown that Dynamenella occurs commonly with chitons living near patches of coarse-grained sediment; the overall character of the habitat and the degree of exposure to wave action do not seem to influence the occurrence of the partnership. A more intimate association of Dynamenella with Acanthopleura is apparently due to the higher level occupied on the shore by the host and to its more sluggish behavior. The symbiont demonstrated a high tolerance to desiccation under chitons exposed to the atmosphere. Dynamenella orients between individual gill filaments as the chiton browses and it appears that the algal material ingested by the inquiline is initially scraped from the substratum by the host. The isopod is regarded as a facultative commensal with a strong attraction for Acanthopleura.