Marine Biology (2+1)

Littorina undulata

Family : Littorinidae

Common Name : Periwinke

Habitat : Marine rocky inter-tidal

Size : 20 mm

Shell non-umblicate, solid, ovately conoid. Columella though appressed by callus, may or may not be violet in general (dark violet in south East coast specimens). Body whorl slightly concavely impressed round the upper part, than convex, evenly rounded without sharp angulation below as in L. s. scabra. Littorina undulata has less elevated spire compared to Littorina scabra.

Lives inter-tidally, invariably at the highest tidal levels on rocky shores commonly clustering in rock crevices during daylight, becoming active at night and crawling on the rocks. These littorines have opercula that completely seal off the aperture of the shell helping to reduce water loss. Grazes on encrusted algae.

Due to its variability some form of L. undulate are rather easily confused with L.s. scabra, but could be distinguished by the following characters.

1. From L.s. scabra it differs markedly in the anatomy of the external reproductive structures. A large penile basal flap being present in undulate, whereas in scabra the entire base of the penis is thickened.
2. L.s. scabra reproduces ovoviviparously while indulata produces a pelagic egg capsule.
3. S. scabra usually inhabits mangroves and other wooden structures such as pilings but undulate is usually found on rocky shores.
4. The shell of L. undulate is smaller (24 mm) at maturity than L.s. scabra (over 40 mm).

Although colour pattern may appear superficially similar, upon close examination it may be noted that in L. s. scabra axial colour markings are applied in a mosaic, the interruptions caused by the deeply incised spiral sculpture, while in L. undulata the markings appear continuous.