Food and feeding in Nudibranchs
All known nudibranchs are carnivorous, and most are specialized predators with a very selective choice of prey organisms. Species within a family usually feed on similar types of prey. For some species metamorphosis of the larval stage into the adult has been demonstrated to be triggered by the presence of the particular prey species. The life span of a nudibranch may also be linked to that of its prey and two categories are recognized;
- Nudibranchs that feed upon ephemeral prey, such as hydroids tend to exhibit several short-lived generations each year.
- Those that feed upon unseasonal prey, such as sponges and dead man's fingers, may live for one year or possibly longer.
Nudibranchs feed by means of a specialized structure called a radula. This organ is only found in molluscs. The radula consists of many rows of chitinous teeth secreted by the radula sac. In cryptobranch dorids the radula is generally broad, with many teeth in each row. Phanerobranch dorids have much narrower radulae, usually with a pair of large teeth for cutting open bryozoans or ascidians. Aeolid radulae have a central horseshoe-shaped tooth with a strong central denticle, usually flanked by smaller cusps. In the Flabellinidae and Eubranchidae there is also a pair of lateral teeth.
The shape and number of radular teeth usually show variation from species to species and radula morphology is an important character used in nudibranch taxonomy. Descriptions of the radulae, though not provided by this field guide are adequately covered in Thompson & Brown Biology of Opisthobranch Molluscs Vol.II.