Acmaea testudinalis
The tortoise-shell limpet is a gastropod mollusk. Gastropods are shelled animals with a single large
foot that encases the animal's stomach. Its relatives include the clam as well as the octopus. Tortoise-shell refers to the brown and white coloration of the limpet's shell. Not bigger than a dime, it has a
hard, cone-shaped shell with a rounded, off-center point. The limpet has a soft body with a large foot
and a small head with two antenna-like protrusions. Its shell is secreted from a fold of tissue called
the mantle. Special muscles attach the limpet to its shell at the base of the point. This limpet is also
known as a Chinaman's Hat. The underside of empty shells are bluish white with a dark brown center.
The tortoise-shell limpet can be found along the North Atlantic coast wherever its close relative the periwinkle lives. Though not as numerous as periwinkles, limpets enjoy the same rocky habitat. The overall shape of the limpet combined with the powerful suction of its foot allows the animal to withstand the pounding surf of the lower littoral zone, the area of the shore just below the barnacles. The limpet moves by rippling the muscles of its foot in a series of waves. This undulating motion can be witnessed on the glass of an aquarium by a keen eyed observer. Limpets have no trap door or operculum to protect their soft bodies so they cling tightly to the rocks at low tide to keep from drying out. As a testimony to their clinging ability, some mines built for attaching to ships in World War II were called "limpet mines".
At high tide or in tide pools limpets glide along in search of food. Limpets use a long thin tube-like
toothed-tongue or radula to rasp algae off the rocks. On its feeding forays, the animal extends its two
tentacles in front of its body to determine food and warn of enemies. The starfish is the most common eater of tortoise-shell limpets. While we do not eat limpets locally, South African limpets grow
much larger and are harvested by people. When the hungry limpet eats its fill or its internal clock
warns of an ebbing tide, he returns to a special portion of the rock known as its home-spot. In areas
where rocks are not granite, there are notable hollows where the animals usually rest.
Cheryl A. Page
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