STUDIES ON THE BEHAVIOR OF NASSARIUS OBSOLETUS (SAY) (MOLLUSCA, GASTROPODA)

¹ Marine Biological Laboratory, Woods Hole, Massachusetts 02543. and Department of Zoology, University of Cambridge, Cambridge, England, U.K.

The reactions of specimens of Nassarius obsoletus exposed individually to controlled laboratory stimuli are as follows:

1. Nassarius shows a light-compass reaction, but no optomotor response.

2. On damp slopes Nassarius moves downhill. Submerged Nassarius is generally geonegative but its response is altered by a nearby light source.

3. In clean seawater Nassarius moves downstream.

4. Addition of effluents from damaged animal tissues or from mud causes a reversal of rheotaxis.

5. A small but significant upstreaming response is elicited by water of raised oxygen concentration.

6. The upstreaming response to olfactory stimuli can be abolished when unfavorable stimuli (hypo-or hypersalinity) are simultaneously present.

7. Water which has passed over living, intact Nassarius is attractive to other individuals of the species Nassarius, the attraction not being due to faeces.

8. When simultaneously presented with substrates of different kinds, mud snails accumulate on those richest in diatoms and bacteria.

9. The behavior of an individual Nassarius is greatly affected by the behavior of others around it. Members of a group of Nassarius in the laboratory or in the field show a strong tendency to conform in their direction of movement, thus producing schooling. The orientation of schools in the field was that expected from the behavior of the majority of individuals in the laboratory.