ABSTRACT: To date, only 3 species of the sponge genus Plakina Schulze have been identified in the Mediterranean: P. monolopha, P. dilopha and P. trilopha. These species are distinguished on the basis of the presence of a particular spicule type (lophocalthrops) with 1, 2 and 3 lophate actines, respectively. In a survey of plakinids on vertical walls and submarine caves in the Mediterranean around Marseilles, France, we found 4 different morphotypes of what would normally be identified as P. trilopha (i.e. with trilophose calthrops). However, slight but consistent differences in morphological characters and ecology led us to doubt the conspecificity of these morphotypes. Genetic divergence and reproductive isolation between morphotypes were investigated through allozyme electrophoresis. It was found that all 4 morphotypes were reproductively isolated from each other, with diagnostic loci between any pair of morphotypes compared. Genetic identities between morphotypes ranged from 0.49 to 0.83. The genetic differences found between the morphotypes indicate that these should not be considered conspecific. Once species boundaries were delimited by genetic data, diagnostic morphological characters for each species could be found.

KEY WORDS: Porifera . Sponge . Plakina trilopha . Allozymes . Cryptic speciation . Genetics

Published in MEPS Vol. 138 (1996) on July 25
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996