MIYAMAE, J.A.*; MERZ, R.A.; Swarthmore College; Swarthmore College: Siphons, snails, and odor trails:Shell morphology and scent-tracking in marine gastropods

Gastropod shells exhibit an exuberant diversity of form, the functional significance of which has often been associated with predation. Shells differ in the presence or extent of elongation of the siphonal canal, which covers the snail�s fleshy, tube-like siphon. The siphon draws water into the body of the snail, aerating the gills and bringing chemical scents to the osphradia. We hypothesize that an elongated siphonal canal restricts the position and movement of the siphon and, therefore, will increase the time for an animal to detect and track down the source of a scent compared to a snail with a reduced siphonal canal (which permits free movement of the siphon). Eight gastropod species (representing seven prosobranch families) were studied. Experiments were conducted in a still-water tank and the response of each individual was timed under two conditions: facing towards and away from a food scent released into the water. The relative response of species differed with the degree of elongation of the siphonal canal. Species with the most elongated canals (i.e., > 45% of aperture length; e.g., Busycon spiratum, Murex pomum ) generally take 2 to 10 times longer to detect and locate a scent when facing away rather than towards a scent source. In comparison, species with little or no siphonal canal (e.g., Ilyanassa obsoleta, Oliva sayana ) are equally proficient at locating a scent source, regardless of orientation. The siphonal canal may function as protection against partial predation of the siphon; however, its presence restricts the movement of the siphon and imposes a delayed response in scent tracking.