Morphological and ecological relationships of two clionid sponges

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Abstract
Cliona vastifica and Cliona lobata, collected from 90–330 m depth, were found excavating shells of Glycimeris glycimeris and Pecten magellanicus (Mollusca, Bivalvia) off the coast ofBlanes (northwestern Mediterranean). Although the external appearance of the two sponge species was very similar, they could be well characterized by their different spicule complement. However, their excavating patterns in shelly substrates could be easily confused at first sight, mainly because ofthe small sizes of chambers and ducts. Some of the morphological parameters studied are found to display the same trends in both species: the mean projected area of chambers is positively correlated with the mean projected area of papillae and in both cases data follow significant linear regression curves; the mean number of chambers per cm2 of infested substrate surface is negatively correlated with the mean area of chambers, as well as the mean number of papillae per cm2 of infested substrate surface with the mean area of papillae, both relationships fit linear regressions. However, significant differences between the species are exhibited when other morphological measures are compared: papilla projected areas (p < 0.001), chamber projected areas (p < 0.05) and the number of papillae per chamber (p = 0.01). Two different ways to estimate the amount of sponge in a given infested shell are suggested: 1) as mm2 (surface of projected area) of choanosorne inside the substratum and 2) as wet weight (mg), both related to the number of papillae per ern- of infested substrate surface.