Interspecific variability in internal anatomy in Terebellides Sars, 1835 (Annelida, Trichobranchidae) revealed with micro-CT

The number of new species described of the genus Terebellides Sars, 1835 (Annelida, Trichobranchidae) in the eastern Atlantic Ocean has greatly increased in the last years. Eleven of these species, all originally described in NE Atlantic Ocean, from the Barents Sea to the Gulf of Guinea, have been studied using micro-computed tomography (micro-CT) thus revealing interspecific differences in several elements of the internal anatomy such as the proportion between stomach regions and size of nephridia, and in the number of lamellae in the digestive gland. Two stomach morphotypes have been distinguished regarding differences in relative length between regions, as well as two morphotypes of nephridia according to their size and wall thickness, and four types of the digestive gland regarding their number of lamellae. Differences in nephridia sizes is the only character apparently related to the geographic distribution of species (i.e. NE Atlantic vs. Gulf of Guinea) but examination of more taxa is needed. A third distinct region was distinguished in the stomach, named here as mid stomach, that differs from the fore and hind stomach in epithelia thickness and by lacking connective muscular sheath. The potential of the micro-CT technique in the search for internal anatomical characters with taxonomic value is discussed.