on exposed shores. It is often found in damp hollows, but does not particularly seek crevices. It feeds by scraping minute algae and grasping pieces of seaweeds. Each individual rests in the same place and wears a slight depression in the rock into which the shell fits exactly. It is hard to remove when attached to the rock with its foot (Edmunds, 1978). Nerita senegalensis (Family Neritiidae) has shell height and width almost the same length, 15–20 mm, with teeth occurring on the outer lip of aperture. It has a pleated collumella with irregular tubercles and very fine spiral ridges on shell. This species has a dark grey color with small paler markings and sometimes uniformly yellow color. This is one of the commonest gastropod species on West African rocky shores, occurring from low tide level to the upper shore. It usually rests in crevices when the tide is out, and may also be found on the open rock and in rocky pools. In Senegal, it extends into rocky estuaries (Yankson and Kendall, 2001). Three species of the gastropod family Littorinidae are common on the West Africa shore. Littorina punctata has a shell height of about 8–15 mm, color brown or grey with white markings in spiral rows often giving a checked appearance. This species is usually common on all rocky West African shores, occurring from the middle to upper parts, though young specimen occur lower down and in rock pools (Yankson and Kendall, 2001). Littorina cinguilifera has a shell height of about 8–12 mm, color alternating brown or grey and white bands, the darker bands sometimes interrupted with white dots especially near the top of the whorl. This species occurs from the middle to upper parts of rocky shores and extends into rocky estuaries. It is usually rarer than the previous species though common in Sierra Leone, it is rare in Senegal and probably Nigeria but extends to Cameroun (Yankson and Kendall, 2001). Littorina angulifera (Littoraria angulifera) Thais species (Muricidae) have wide oval aperture, notched at base; columella callosity smooth and arched; operculum is horny thin, nucleus at outside edge; sculpture of rounded or pointed tubercles. This genus is distributed worldwide. The species found on the West Africa shore are Thais forbesi, Thais nodosa, Thais callifera and Thais haemostoma. Thais nodosa shell height is about 40–55 mm, width somewhat less; body whorl large, spire short and blunt; outer lip