Biogeographical Distribution

Aplysia are known to occur worldwide throughout tropical and temperate waters. In 1960, Eales determined that there were 32 species in total although today the estimate has gone up to around 50 species. Unfortunately most of the work that has been done on some of the more obscure Aplysia species has been primarily based the analysis of fixed specimens, with often only few examples of each. The problem with this is that many species of Aplysia are similar enough to be mistaken for one another (Carefoot 1987).

Australia is thought to host the largest diversity of species (14 described), second only to the number found around New Zealand (Carefoot 1987). Some Aplysia have only a limited distribution, with many species being endemic to small atolls and islands.  Only 3 species are known to have a circumglobal distribution, namely A. dactylomela, A. Juliana and A. parvula (Marshall & Willan 1999).