6. Gastropods as Parasites and Carnivorous Grazers: A Major Guild in Marine Ecosystems

Parasitism and similar life styles such as carnivorous grazing or mucus feeding without killing the prey are important in marine gastropods. Some of the most diverse living gastropod families have this feeding behavior. Taxonomic uniformitarianism is the most important tool to infer parasitism or similar life styles in fossil gastropods. The extant family groups in question (Eulimidae, Epitoniidae, Pyramidellidae, Architectonicidae, Coralliophilinae, Ovulidae, Cerithiopsidae and Triphoridae) originate mostly in the Late Cretaceous (Cerithiopsidae in the Middle Jurassic) and Paleocene. They are performing an ongoing adaptive radiation and some of the mentioned families belong to the most diverse gastropod groups forming a considerable part of marine ecosystems regarding species richness and relative abundance. At the same time, origination and radiation of the carnivorous, commonly predatory Neogastropoda took place. This points to a trophic revolution in Gastropoda that forms an important aspect of the Mesozoic Marine Revolution. Most modern parasitic gastropods are small, high-spired, show high diversity and low disparity within families and belong to Apogastropoda. By analogy, some extinct gastropod families which show the same properties might have lived parasitic too (e.g., Pseudozygopleuridae, Zygopleuridae, Meekospiridae, Donaldinidae). However, this will remain speculative to a large degree until direct host associations are found. Direct evidence for parasitism is exceptional with the Palaeozoic platyceratid/crinoid interaction being one of the best studied examples. In Gastropoda, functional shell morphology may help to identify parasitism in the fossil record but this field is scarcely studied.