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A phylogeographic study of the genus Pentapora (Bryozoa ; Cheilostomata) in North West Europe and the Mediterranean

The bryozoan genus Pentapora comprises colonies that form honeycombed, domed structures, with dicotomic or laminar branches and a diameter of 20–30 cm or up to 1 m. They grow as epibionts or develop micro-reefs on rocky seabeds. The geographic distribution is described from the North Atlantic to the Mediterranean. Morphological studies have refined the taxonomy and Gautier (1962) considered P. fascialis and P. foliacea to be different species, later the two species were given the status of subspecies (Zabala and Maluquer, 1988 ; Alvarez, 1991). Recently, the two forms have been classified as a single species P. fascialis (Hayward and Ryland, 1999 ; Chimenz-Gusso et al., 2005). Our purpose is to investigate the phylogeography of Pentapora using molecular methods, combined with morphological analysis of recent specimens collected from different regions of Europe, in order to clarify species status. Sampling of Pentapora colonies from UK and Mediterranean populations was conducted between July 2006 and September 2008. Morphological features and skeletal structures were analyzed using SEM techniques. DNA was extracted from fresh samples and sequence analysis of mitochondrial and nuclear genes conducted. Comparison of Atlantic versus Mediterranean samples revealed no differences in morphology and autozooid structure. SEM images revealed diversity in skeletal ultrastructure (i.e. appearance of mineralogical crystals which compose frontal wall layers). These differences may be attributed to variation in the mineralogical composition of the frontal wall due to seawater temperature conditions experienced by the colonies during growth. Investigations of avicularia revealed that a hypertrophied avicularia sporadically replaced the normal-size avicularia in both fossil and recent species, including in Mediterranean Pentapora. The absence of this giant avicularium in the Atlantic Pentapora, could be considered as a possible critical character in discriminating species of Pentapora. Bayesian analysis revealed genetic differentiation between Atlantic and Mediterranean basins, with Atlantic populations occurring as a monophyletic sister group arising from the Mediterranean populations. Hypotheses for these patterns are discussed along with the taxonomic implications of these findings.

Bryozoa; Pentapora

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