A picture is worth a thousand words: novel photographic evidence on the anatomy of the digestive system of three shipworm species (Bivalvia, Teredinidae)

Adult shipworms (Bivalvia, Teredinidae) have greatly elongate bodies, and thus, the organs have a different orientation than those of other bivalves. Studies on the anatomy of the digestive system have been carried out in a number of genera and species in the Teredinidae, but are now over 50 years old and most were carried in only a few preserved specimens. These studies contain descriptions and line drawings, but high-resolution images do not exist, except for Lyrodus pedicellatus that was recently studied using modern techniques. Thus, we present high-resolution images of fresh specimens of three teredinid species, representing three genera, to show the different features of each organ of the digestive tract and intra- and inter-specific differences. Most of our observations concur with, but some differ from previous descriptions. One observation in Teredo navalis showed, for the first time, the foot covered by a membrane with corrugated aspect, which the function is not yet understood. Another observation in the same species showed that the caecum and intestine have strikingly different colourations in specimens in overcrowded conditions when compared with those in uncrowded conditions. This may indicate that the former resort more to filter feeding to avoid the complete destruction of their habitat. In Psiloteredo megotara, the digestive gland seems to cover the caecum, as it does in Nototeredo norvagica and differing from a previous line drawing for the former species. Faecal pellets were observed in N. norvagica and P. megotara, which may indicate a more complete utilization of wood in these species.