Tuberculation in spatangoid fascioles: Delineating plausible homologies

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Abstract

The existing definition of spatangoid fascioles as a narrow band of minute tubercles (miliaries) is inadequate. One reason is that many intermediates between the presence of indisputable fascioles and their total absence are known. Although fascioles are widely used in the classification of spatangoids, diversity of fasciole tuberculation has largely been ignored. We examine fascioles in about 100 spatangoid species, focusing on the earliest manifestations of fascioles (both developmentally and phylogenetically) and on their variable tuberculation. Qualitative observations are complemented by quantitative analyses (ANOVA and PCA) of 21 species. Three types of fascioles are defined according to tubercle pattern: protofascioles for localized concentrations of miliaries; parafascioles for bands of miliaries with a progressive transition to the surrounding tuberculation; orthofascioles for strongly differentiated, well-circumscribed bands of miliaries. Ontogenetic, architectural, ecological, and taxonomic variations of these three patterns are qualitatively and quantitatively investigated. We attempt to delineate plausible homologies, origins, and subsequent evolution of the different kinds of fascioles.

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