Anatomy of the many feeding types in polyplacophoran molluscs

Seven different ecological feeding strategies have previously been identified among chitons, despite their apparent morphological homogeneity. These include: detrivores, herbivores, omnivorous grazers, carnivorous grazers, specialist spongivores, epizoophagous feeders, xylophagous wood-dwelling species and true predators. The majority of species among common intertidal chitons appear to be omnivorous grazers. Here, we examined the gut morphology, and radula morphology, in species from various feeding types. The proportionate length and mineralization of the radula are not strongly correlated with feeding type, but these characteristics could be refined and later used to exclude particular habits where no other ecological data are available. Gut length in chitons follows classical gut foreshortening, with ambush predators having a short intestinal tract forming a single major loop, whereas obligate herbivores having dramatically long intestinal lengths with multiple coilings. Multiple feeding strategies, and concomitant adaptation of the digestive system, can be observed among phylogenetically closely-related taxa. Niche partitioning through dietary specialization, even among co-occurring omnivorous grazers, may speculatively underpin the success of chitons in the Northeast Pacific and other regions.