26 June 1987
Vol 236, Issue 4809

About The Cover

Caribbean sponges, similar to the large barrel-shaped Xestospongia muta, are almost exclusively heterotrophic, whereas many of those on the Great Barrier Reef rely heavily on symbiotic cyanobacteria for much of their nutrition. The incidence of symbioses in the two regions is comparable, but those in the Caribbean, like X. muta, typically have only a thin layer of red-brown symbiont—containing tissue. See page 1654. [Clive R. Wilkinson, Australian Institute of Marine Science, Townsville MC, Queensland 48101, Australia]