The functional morphology of the digestive system in the carnivorous intertidal isopod Eurydice

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Abstract
A detailed study of the diet of Eurydice pulchra Leach and Eurydice affinis Hansen, sand beach isopods, reveals that these species are almost wholly carnivorous. A description of the mouthparts, together with their mode of functioning, derived both by direct observation and an interpretation of their structure, shows how they are adapted for tearing and bolting animal food material.The gross morphology of the alimentary canal is described, including a detailed study of the foregut, which appears to be relatively simple in structure, lacking a cardiac region. An interpretation of the functioning of the foregut is given, from which it is apparent that this region serves to mix rapidly bolted food with digestive gland enzymes, and also to squeeze out liquid food matter which is channelled into the digestive glands. The bulk of the solid food is passed back into the distensible anterior hindgut, where it may be stored for up to three weeks undergoing gradual digestion. The hindgut lacks a peritrophic membrane, but anal irrigation occurs.The digestive system is compared with that of herbivorous and omnivorous isopods. It shows structural and functional modifications related to the carnivorous mode of life, which appear to be characteristic of Eurydice and are related to the general ecology of the genus.

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