Hydatina physis Linnaeus, 1758
Description: Shell light in weight, inflated, spire slightly sunken so that apex is truncated. Shell surface smooth, glossy, or irregularly dented in large shells. Aperture wide, outer lip thin and sharp, inner lip with thin white glaze on parietal wall. Colour white with numerous black or dark brown spiral bands of varying width.
Size: NSW specimens up to 55 mm in shell length.
Circum-global in tropical and temperate waters. In eastern
Intertidal and shallow subtidal. The animal is a
specialised worm feeder, eating only cirratulid
polychaete worms. In NSW the species is most frequent on seagrass flats
but it also occasionally encountered on exposed rocky shores at low
tide. Uncommon in NSW.
The animal is spectacular (Fig. 2), with purple folds (enlarged head
shield, metapodium and foot) much wider than the shell, edged with
almost luminous blue. The Sea Slug
Forum provides more illustrations of the animal (http://www.seaslugforum.net/find/hydaphys).
anatomy of this species was described by Rudman (1972).
Fig. 1: Narooma, NSW (C.107520).
Fig. 2: Live animal. Inscription Point, Kurnell, NSW, 2009. (Photo Jack Hannon).
Copyright Des Beechey 2017