Gastropod skeletal defences: land, freshwater, and sea compared
Vita Malacologica , Volume 13 p. 1- 25
Predation is a primary agency of natural selection affecting the evolution of skeletal form in gastropods. The nature of antipredatory defence depends on how predators attack their prey as well as on the types and quantities of resources that are available to the potential victims. Here I review the five main methods of predation on shell-bearing gastropods (swallowing prey whole, apertural entry, drilling, shell breakage, and partial consumption) and 31 categories of shell and opercular defence that are effective at one or more of the three stages of predation (detection, pursuit, and subjugation). These categories are evaluated for marine Palaeozoic, marine Late Mesozoic to Recent, freshwater, and terrestrial environments. The five types of predation are common in most environments, but drilling and partial consumption are absent in freshwater and unlikely in the Marine Palaeozoic, and partial consumption may be rare on land. The fewest specialized defences are found in freshwater, followed by the marine Palaeozoic and Recent terrestrial environments. There has been a sharp rise in the number of defence types and in the degree of antipredatory specialization in marine environments from the Palaeozoic to the Recent, particularly among defences at the subjugation and pursuit phases of attack. The small number of defences and the passive nature of shellbased protective traits in terrestrial gastropods contrast with the high diversity of antipredatory adaptations, including those related to aggression and speed, in other land-dwelling animal clades.