Shell massive, solid, of 5-6 whorls, of which the body whorl makes most of the volume. Whorls with strong triangular knobs on a spiral keel; body whorl with an additional subsutural keel with projecting knobs and with a few indistinct spiral cords; the entire surface with fine, irregular spiral striae. Umbilical chink surrounded by a broad thickened rim. Aperture ovate, with the simple outer lip grooved spirally inside juveniles, smooth inside in well-grown specimens, terminating anteriorly in a small, short siphonal canal.
outside of a plain greyish or yellowish tan color, inside of aperture pale orange, juveniles with darker lines in grooves inside the outer lip.
common size :
It is distinguished from the native Thais haemastoma (Linnaeus, 1758) by having a strong keel which gives the spire a pagoda-like aspect, and in having a much paler color inside the aperture. Rapana venosa and Rapana rapiformis both have a flatter spire and much more swollen aperture.
BIOLOGY / ECOLOGY
Thais lacera lays clusters of cylindrical egg capsules attached to the substrate, which differ from capsules of the native Stramonita haemastoma (Linnaeus, 1758) in being rounded and poined at their tip, instead of flaring and rectangular. The larvae are pelagic, planktotrophic. Hanafy (1996) studied on Egyptian populations of this species the incidence of imposex (an anomaly also found in other Muricidae, induced by contaminants from anti-fouling paints used on ships, and where the females develop a non-functional penis).
on rocks, near sea level.