On the Number of Rays in Asterias tenuispina Lamk. At Bermuda

1. The modal number of rays in Asterias tenuispina is 7. The range in ray number is from 2 to 9. 2. The 7-ray condition is uniformly the most frequent, even in widely separated localities. 3. The modal ray number is the same for animals with subequal rays as for those with a group of regenerating ra...

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Bibliographic Details
Published in:The American naturalist 1915-01, Vol.49 (577), p.28-36
Main Author: Crozier, W. J.
Format: Article
Language:English
Subjects:
Animals
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Summary:1. The modal number of rays in Asterias tenuispina is 7. The range in ray number is from 2 to 9. 2. The 7-ray condition is uniformly the most frequent, even in widely separated localities. 3. The modal ray number is the same for animals with subequal rays as for those with a group of regenerating rays. 4. The evidence indicates that, most commonly, A. tenuispina has 7 rays before it undergoes autotomy, that it divides into 3-ray and 4-ray portions, and that each of these parts regenerates 4 rays. 5. Regenerating rays tend to appear in bilaterally disposed pairs, as regards size. 6. There is no evidence that self-division occurs often in the life of individuals, though possibly it does. 7. New rays may be added at any point on the disc. 8. The number of madreporites varies from 1 to 5, and is to some extent correlated with the number of rays; it is not correlated with the size of the animal. 9. Double or triple madreporites occur in about 5 per cent. of the individuals.
ISSN:0003-0147
1537-5323
DOI:10.1086/279451