Hydatina physis (Linnaeus, 1758)
Common in the Solitary Islands Marine Park. Circum-global distribution in tropical waters including the Indo-Pacific and Atlantic oceans. Common throughout Australia.
Often found in shallow waters, especially coastal rockpools, usually less than 5 m deep. Prefers sandy substrate and is more active at night.
When feeding the animal everts a muscular black feeding tube with which it probes crevices and worm tubes for cirratulinid polychaete worms. The shell has diminished as a protective device, it is no longer able to withdraw into the shell and the protective operculum has disappeared. Grows to 4 cm.
Gary Cobb, David Mullins, Nudibranchs Encyclopedia, 2nd Edition, 2015. Publishers Thomas Slone, Masalai Press and Tim Hochgrebe, Underwater Australasia. p.49.
Australian Museum, Sea Slug Forum. http://www.seaslugforum.net/showall/hydaphys. Accessed 24/09/2018.