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.

本数据集收录了弗朗西斯（Francis, 1980）在论文《汤加塔布岛裸鳃类（nudibranch）血红六鳃海蛞蝓（Hexabranchus sanguineus）的栖息地、食物与繁殖活动》中采集的该类群的发生记录。六鳃海蛞蝓属（Hexabranchus Ehrenberg, 1831）的分类学现状较为混乱，亟需系统修订。目前该属已描述物种逾20种（参见Thompson, 1972），其中多数仅以体色模式差异作为分类依据。部分学者（Bergh, 1900；Eliot, 1904；Thompson, 1972）认为，诸多已命名的所谓"物种"仅为血红六鳃海蛞蝓（Riippell & Leuckart, 1828）的体色变种。该属是否可将体色模式作为有效分类学特征，仍有待进一步验证。尽管如此，下文仍将完整描述汤加地区六鳃海蛞蝓的体色模式，以便在未来证实体色确为独特分类特征时，可为后续比较研究提供参考。现有研究显示，已描述的各变种间外部与内部形态差异极小（Eliot, 1904），但针对汤加地区该类群的形态学调查尚未开展。鉴于目前尚未发现有效的专属分类学特征，本研究将汤加地区的六鳃海蛞蝓归入该属的模式种——血红六鳃海蛞蝓（Riippell & Leuckart）。其余已被描述的"物种"，本文均将其视为血红六鳃海蛞蝓的体色变种。