Janthina janthina (Linnaeus, 1758)
Description: Shell lightweight, wider than high, aperture more than half shell length. Spire whorls rounded, last whorl angled at periphery. Whorls sculptured with irregular weak axial growth lines, following curves of outer lip, and several spiral grooves, more prominent on base. Outer lip (when unbroken) with shallow sinus at periphery. Umbilicus closed. Colour pale violet on spire whorls and above periphery of last whorl, purple below periphery of last whorl.
Size: Up to 40 mm in length.
Distribution: Worldwide, in tropical and temperate seas. Known from all Australian states.
Habitat: Pelagic; found washed up on ocean beaches; common.
Comparison: This species is distinguished from others in the genus by its squat form - the other species are taller - and by its colouration of pale violet above the periphery and purple below.
Synonymy: Janthina violacea Röding, 1798 and Janthina planispirata A. Adams & Reeve, 1848 are the most common synonym in Australian literature. Laursen (1953) listed 32 synonyms in total.
Remarks: This species is viviparous i.e. the eggs are retained internally in the oviduct where they develop into veligers. The veligers are released into the water where they live freely in the plankton, eventually transforming into adults. The biology was described by Wilson & Wilson (1956) and the feeding habits by Ganapati & Subha Rao (1960).
Figs. 1,2: Putty Beach, Kilcare, NSW (C.362501)
Copyright Des Beechey 2008