Molecular and morphological systematics of Gray, 1847 (Mollusca: Gastropoda: Heterobranchia: Aplysiomorpha).

Molecular and morphological data from newly collected specimens and a review of the literature and type material indicate that the widespread tropical sea hare is a species complex of five genetically distinct taxa. The name is retained for a widespread species in the Indo-Pacific tropics. is endemic to the eastern Pacific. , and a new species described herein are restricted to the tropical Atlantic, with partially overlapping ranges in the Caribbean region and St. Helena. The temperate Pacific species is also distinct and endemic to temperate southeastern Australia and New Zealand. These species of constitute highly divergent lineages and most contain unique internal anatomical characteristics, particularly in the male reproductive morphology and shell shape, making them relatively easy to identify upon dissection. However, externally all these species are extremely variable in colour pattern and morphology and are virtually indistinguishable. This is particularly problematic for identification in the Atlantic Ocean where three species co-occur in the Caribbean region.