A scanning and transmission electron microscope study of the digestive caecae of the marine wood boring isopods Limnoria tripunctata and Limnoria quadripunctata, was undertaken. Two cell types were identified, containing structures indicative of absorption, secretion and storage. Cell types were distinguished according to size, the largest cell type having a large free surface area, a well developed microvillous border and a cytoplasm containing both iron and what were believed to be proteinaceous granules. The small cells possessed endoplasmic reticulum and lipid granules. This study suggests that large cells were responsible for absorption and storage of iron, whereas the small cells were secretory and capable of storing lipid. Residence time for wood in the gut was determined to be approximately two hours for both Limnoria tripunctata and Limnoria quadripunctata. This rapid gut transit time is relatively short compared to other cellulose digesters, suggesting that Limnoria is an inefficient digester of wood.

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