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Biol Bull 131: 219-229. (October 1966)
© 1966 Marine Biological Laboratory
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DISTRIBUTION OF URCEOLARIA SPINICOLA (CILIATA, PERITRICHIDA) ON THE SPINES OF THE SEA URCHIN STRONGYLOCENTROTUS DROEBACHIENSIS

C. DALE BEERS 1

1 Department of Zoology, University of North Carolina, Chapel Hill, North Carolina 27514, and Mount Desert Island Biological Laboratory, Salisbury Cove, Maine

1. At Mount Desert Island, Maine, Urceolaria spinicola is of general occurrence on the spines of Strongylocentrotus droebachiensis. Two aspects of the urchinciliate relationship were studied, largely on urchins from Frenchman Bay: the occurrence of the ciliate on urchins of different sizes and its distribution on spines of different lengths.

2. The density of the urceolaria population was highest on urchins measuring 24-60 mm. in diameter (test only), assumed to be 2-5 years of age (average number of ciliates per spine, 27). Smaller and therefore younger urchins (diameter, 9-18 mm.) had fewer per spine (average number, 9). On the largest urchins (62-74 mm.), assumed to be at least 6 years of age, urceolarias were extremely scarce (average number per spine, 3). Indeed, many urchins of this size had no ciliates whatsoever.

3. The distribution on spines of different lengths was studied with special care on 41-mm. urchins. The smallest spines (length, 0.6-0.9 mm.) had relatively few urceolarias per spine (average number, 9), whereas spines measuring 1.0-4.9 mm. in length had the largest number per spine (average, 36). The remaining spines (length, 5.0-16.0 mm.) were seriated according to length. On all the sizes, the average number of urceolarias per spine was well below the maximum of 36 and the number decreased as the length of the spine increased. Thus, many of the longest spines lacked ciliates. On spines measuring 0.6 to about 3.0 mm. in length, the urceolarias were distributed uniformly along the length of the spine; on spines longer than 3.0 mm., they were concentrated on the basal half of the spine.

4. The distribution of U. spinicola on the spines could not be related convincingly to any of the following factors: degree of ciliation of the spines, contact of the spines with one another, presence of water currents in the environment or availability of bacterial food on the surface of the urchin. Therefore, it is concluded tentatively that the distribution is related to the intrinsic properties of the spine epidermis, perhaps to the distribution of gland cells in it.






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Copyright © 1966 by the Marine Biological Laboratory.