Shell Repair in the Gastropod, Marisa rotula

Abstract

An ordinary tropical fish aquarium, with a six gallon capacity, was equipped with an air pump and a filtration system to provide a clean, well oxygenated environment for the snails used in the experiment. The water was changed approximately every two weeks to provide a renewed calcium supply for normal shell growth. Lettuce and other vegetable matter was fed every other day throughout the experiment. Twenty specimens of Marisa rotula, all hatched at the same time and from the same batch of eggs, were placed in this environment. The snails were numbered consecutively from one to twenty and the appropriate number was painted on each snail3. The snails numbered one through ten were designated the Control Group and the snails numbered eleven through twenty were designated the Experimental Group. No pre-sorting was done to determine which group each snail would fall into. The numbers were painted on at random with no attempt to select certain ones for a certain group. Consequently the Experimental Group, overall, was a few thousanths of an inch larger than the Control Group. Each snail kept the original number given it throughout the experiment, allowing the authors to keep an accurate account of the progress of each snail during the entire experiment. Measurements of the height of each snail were taken periodically from 31 May 1959 to 16 November 1959. The height is here understood to be from the highest point of the aperture, across the apex region, to the lowest point at the bottom of the curvature of the shell. All measurements were made with vernier calipers which could be read directly to 1/1,000th inch.