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Structure and function of the anal sacs of Bonellia viridis (Echiura: Bonelliidae)

Published online by Cambridge University Press:  11 May 2009

R. R Harris
Affiliation:
Department of Zoology, University of Leicester, University Road, Leicester

Extract

The structure of the anal sacs of the echiuran Bonellia viridis Rolando was studied using SEM, TEM and light microscopy. The characteristic ciliated funnels which open into the coelom and connect it to the lumen of the sac were observed live by interference contrast light microscopy. Clearance of the extracellular marker inulin from the coelomic fluid (Vc = 9·6 ± 1·9 ml 100 g−1 wet weight of animal day−1) indicated that a filtrate of coelomic fluid is produced by the ciliary activity of the funnels. The flow of this filtrate into the sacs is unidirectional. Comparison of the ionic composition and osmolality of the anal sac fluid with the coelomic fluid, and surrounding sea water, indicates that the filtrate passes unmodified by absorptive or secretory processes to the outside. Thus the sacs do not appear to have a clear iono- or osmoregulatory function. During osmotic uptake of water in low salinities the rate of clearance of inulin by the anal sacs did not increase, indicating that their role in volume regulation is insignificant. The reddish-brown granules in the epithelium and lumen of the organ (which give the sacs their characteristic colour) may be important excretory products, and the primary function of the sacs their elimination.

Type
Research Article
Copyright
Copyright © Marine Biological Association of the United Kingdom 1981

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