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Platyceras

PLATYCERAS The first few whorls of the shell are loosely coiled but rapidly enlarging, so that the last whorl is inflated and more or less cap shaped. Sinuous growth lines produce prominent ridges and furrows that indent the shell margin. These had no functional significance but followed the shape of the object on which the animal lived--hence the variation between individuals. Habitat: Commensal with crinoids, Platyceras shells are occasionally preserved in their life position on the host. © 1992 Cyril Walker, David Ward .