BEHAVIORAL ASPECTS OF RIGHTING IN TWO ASTEROIDS FROM THE PACIFIC COAST OF NORTH AMERICA

¹ Oregon State University, Marine Science Center, Newport, Oregon 97365

1. The behavioral aspects of righting were studied in the asteroids Henricia leviuscula and Leptasterias aequalis by detailed observations on the righting method, including leading pair of arms and righting time.

2. Somersaulting characterized the righting method employed by both species. In contrast, the folding over method, and a combination of folding over followed by somersaulting were used only by L. aequalis. Somersaulting appears to be characteristic of the entire class Asteroidea.

3. Both species are active during the pre-righting period, suggesting that there is no entirely motionless quiescent period.

4. The righting response was clearly present in H. leviuscula at the beginning of the righting reaction. However, in L. aequalis, it appeared later.

5. H. leviuscula, exhibited a tendency to utilize arms C/D more as the leading pair of arms than other arm pairs. In L. aequalis, arm pairs A/B, B/C, E/F, and F/A were used more as leading arms than arm pairs C/D and D/E. In both species the preference for certain arms to lead in righting reaction is a species rather than an individual characteristic. Leading arms are not adjacent to the madreporite.

6. The time required for righting in both species was very variable. Differences in righting time between species appears to be an expression of differences in morphology rather than of environmental variables or behavioral modes.

7. There was a significant relationship between the body size and the righting time in both species of sea stars, with smaller individuals righting faster than larger.

8. Mechanical stimulation affected the arms used in righting in L. aequalis. The arm used to turn the sea star over was used less frequently as a leading arm. It is possible that the results of some previous studies are in error because of this response. However, no such effects were observed in H. leviuscula.

9. Since there was no difference in the righting time between the somersaulting and folding over method in L. aequalis, neither method would appear to be more advantageous for survival in nature.