A species believed to be more primitive than C. natans (Grontved) (type species of Calliacantha Leadbeater) has been described and illustrated by means of light and electron microscopy of dry whole mounts prepared in situ from freshly gathered sea water, mainly in South Africa but supplemented by one gathering from Britain. The characters of the species include a variable number of anterior spines, commonly 5 but sometimes 4, 6 or (exceptionally) 7, with structural continuity and therefore a 1:1 relation between spines and longitudinal costae, excluding fortuitous duplications or omissions affecting single loci, adjacent spines being otherwise separated by no more than single transverse costal strips. Numerical reduction in longitudinal costae is also demonstrated, the details being variable as in C. natans. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.
