Morphological and genetic variation in Hanleya nagelfar and Hanleya hanleyi (Mollusca: Polyplacophora) in the Northern European Atlantic and the phylogenetic position of Hanleyidae based on nuclear and mitochondrial genes

Abstract

Large specimens of the spongivore Hanleya nagelfar (Mollusca: Polyplacophora) differ noticeably from the smaller congeneric H. hanleyi, but many scientists have reported that small specimens are very similar and perhaps identical. The debate of their relationship has been ongoing for over 140 years, without reaching a conclusion. This thesis uses genetics combined with statistical analyses on morphometric characters previously used for separating the two species, as well as examination of girdle armature and radulae, in the attempt to resolve the relationship of the chitons. Partial sequences of the genes 18S rRNA, 16S rRNA and cytochrome B are used to find differences within Hanleya. A Bayesian analysis is used to infer the molecular phylogenetic position of Hanleyidae among Polyplacophora for the first time. Statistical analyses find substantial ontogenetic changes in all external diagnostic characters. Radula and cytochrome b variations indicate presence of a hidden species within Hanleya in the Northern European Atlantic.