Records of the nudibranch Hexabranchus sanguineus on Tongatapu island, Tonga

This dataset records the occurrence records of the nudibranch Hexabranchus sanguineus collected for the paper "Habitat, food and reproductive activity of the nudibranch Hexabranchus-sanguineus on Tongatapu island" by Francis, 1980.

The taxonomy of the genus Hexabranchus Ehrenberg,1831 is confused and requires revision. More than 20 species have been described (see Thompson, 1972), many of them based primarily on differences in colour pattern. Some authors (Bergh, 1900; Eliot, 1904; Thompson, 1972) consider the many named species to be merely colour varieties of Hexabranchus sanguineus (Riippell & Leuckart, 1828). The validity of the use of colour pattern as a taxonomic character remains to be demonstrated in this genus. Nevertheless, a full description of the colour pattern of Tongan Hexabranchus is given below to facilitate comparative studies in the event that colour does prove to be distinctive. External and internal morphology appear to vary little among the described varieties (Eliot, 1904) but these features were not investigated in Tongan animals.

In the absence of any distinctive taxonomic characters, Tongan Hexabranchus are here referred to the type species of the genus, H. sanguineus (Riippell & Leuckart). Other described "species" will here be considered simply as colour variations of H. sanguineus.