A Comparative Ethological Study of Strombid Gastropods

Abstract

AbstractThe behavior of ten species of strombid gastropods (Strombus and Lambis spp.) was studied in the Marshall, Hawaiian and Line Islands. Measurements were made in both the laboratory and the field of the MAP's comprising feeding, locomotion, righting of overturned shells, and escape from predators, which reflect significant ecological and morphological determinents of behavior in the Strombacea. All species feed by grazing with the proboscis under the protection of the shell. All Strombids use the MAP Leap during locomotion. The rate of locomotion varies as a hyperbolic function of length; increasing with greater size in the genus Strombus and decreasing in the genus Lambis. Larger animals travel a greater distance with each leap but make fewer leaps/minute. Species of Strombus right their overturned shells by a Kick at the substratum with the operculum, but species of Lambis use the MAP Pull and turn the animal over with the operculum wedged under the shell. Only one attempt is needed in the species of Lambis, but more are used by the faster moving species of Strombus. Intention movements are performed during righting. Species of both genera escape from molluscivorous cones using the MAP's Tentacle Wave, Flip and Run. In the species of Strombus, Flip causes a backward movement of the shell off the substratum, but in species of Lambis the shell restricts the movements and the animal merely turns to one side. Escape locomotion is much faster than normal locomotion, due to the greater distances travelled with each flip by the smaller species of Strombus and the greater number of leaps/minute made by all species. The flip escape response appears particularly adapted for escape from dart-shooting predators. A review of the literature on strombid behavior shows that the behavior of all species within the Strombacea is remarkably similar even though there is great disparity in shell shapes. Because of similarities in soft body parts and behavior, the Xenophoridae should be retained within the Strombacea. It is suggested that the species within the Strombacea evolved in parallel from a common aporrhaid-like stock and the behavior has diverged less than shell form and is therefore a more conservative character in the group's phylogeny than is shell shape. The behavior of a snail can be greatly modified by its shell. Differences in behavior between Strombus and Lambis are attributed to restrictions imposed by the shell and not differences in body movements. Behavior must be adapted to the shell shape and both, of course, reflect the animal's ecological setting.