Habitat: it lives into rocks creeks and under stones, in the meso (the most common one) and infralittoral zones. Distribution: quite common all over the Mediterranean.
Notes: this species, unmistakable in form, is really changeable in outline and in colour pattern. Not much slim, bright, biconic, whorls not much convex. Last whorl is two thirds of total height, suture clear. Typical aperture narrow and stretched, external lip with one shoulder in the upper part while, in the median part, it showes one clear denticulated thickening on the internal margin. Even in the lower part of columella there is a denticulation more or less evident. On the very first whorls of teleconch there are some weak little axial ribs and some spiral grooves undulated reaching the upper margin of the last whorl. Protoconch is also really characteristic. It is made by one oblique carina giving the first whorls of spiral a truncated aspect. Operculum corneous. Colour pattern variegated: on a light ground there are always stains and fiammulae in several colours (either violet or dark brown are the most usual) originating quite a lot of varieties of no taxonomic value. Juvenile specimens are also easily recognizable due to the typical protoconch form. No rare specimens slimmer and tapered in their aspect (form elongata), with the first whorls soluter and turriculate. C. striata Duclos in Chenu, 1846, distinguishable due to an axial and spiral sculpture more emphasized, as well as to the form of lip more expanded in the upper zone and due to a scalariform aspect, was put in synonymia with C. rustica by Moolenbeek & Hoenselaar (1991), temporarily, so it is quoted by CLEMAM too.
During Summer it lays some gelatineous egg capsules, lenticular in form and greenish in colour pattern, which are fixed to algae (to Posi-
donia oceanica too). Larvae are pelagic. It feeds on rubbles and on algae voraciously, using its radula.
The adult specimens average measures are around 15-18 mm in height.