Lined Top Shell

Overview

The Lined Top Shell (Phorcus lineatus) is a robust marine gastropod commonly found on rocky shores across the northeastern Atlantic. Named for the intricate, zigzag patterns on its shell, this species is a familiar sight in intertidal zones where it plays an important role in the local ecosystem.

Appearance

This snail possesses a thick, solid, and conical shell that typically features five to six whorls. The shell's exterior is generally grey, green, or black, decorated with fine, braided, purplish-black or brown zigzag lines. A key identifying feature is a prominent "tooth" or bulge located on the nacreous, mother-of-pearl inner layer near the aperture. As individuals age, the pointed apex of the shell often becomes eroded, revealing the pearly layer beneath. The animal itself is typically pinkish in color, featuring a grey muscular foot and sensory tentacles.

Distribution & habitat

The species is distributed from Morocco in the south to its northern limits in North Wales and parts of Ireland. It favors stable, moderately exposed rocky shores, often inhabiting boulder fields or areas with broken rock. They are primarily found in the mid-shore region, frequently occupying crevices or sheltering under rocks during low tide.

Biology & behavior

Lined Top Shells are active grazers that feed on algae found on rocky surfaces during high tide. They are relatively long-lived, with some individuals surviving for over 20 years. Maturation typically occurs around two years of age. Due to their sensitivity to environmental conditions, they are often studied as bioindicators for coastal habitat quality and the impacts of climate change.