Patellogastropoda: Limpets

Abstract

Limpets share many characteristics with primitive mollusc groups beyond gastropods, including shell micro-structure, morphology of the radula and eyes opening directly into the sea. Their shell is low, conical and with a broad aperture; vision is poor, but they have circumferential perception of their environment through sensory tentacles around the margin of the mantle. Limpets usually colonise intertidal wave-beaten rocky shores, to which they cling by a powerful muscle, by sticky mucus and, in some, by dissolving the rock and forming a pit (‘home scar’); a grazing limpet homes to its scar, in which predation and desiccation are reduced. Some intertidal limpets survive a 60 % loss of the water content in their body. Iron-oxide plated radular teeth remove hardened algal films from rocks. Some limpets are generalist grazers, others feed on kelp; some farm gardens of red or brown algae from which they expel intruders and weed out other algae; in some, sticky mucous trails trap algae and stimulate algal growth so limpets retracing their trails capitalise on food-enhancing mucus. Primitive limpets respire through a gill, others through a cordon of flaps hanging from the mantle around the foot and head. During mating, gonads swell to half the body weight. Many limpets are sequential hermaphrodites: males when young and females later. The externally fertilised egg floats in the sea, a trochophore hatches, becomes a veliger and eventually metamorphoses.