Three-dimensional structure of the shell plate assembly of the chiton Tonicella marmorea and its biomechanical consequences.
The aesthete canals of fourteen chiton species were cast with epoxy, allowing detailed examination and comparison of the entire canal system that infiltrates their valves (shell plates). Some species in this study have been classified without question in the family Mopaliidae (Mopalia ciliata (Sowerby, 1840), Mopalia lignosa (Gould, 1846), Mopalia spectabilis Cowan and Cowan, 1977, Mopalia swanii Carpenter, 1864, Katharina tunicata (Wood, 1815)), while other species have been placed in that family by some workers but not others (Dendrochiton flectens (Carpenter, 1864), Dendrochiton lirulatus (Berry, 1963), Tonicella insignis (Reeve, 1847), Tonicella lineata (Wood, 1815), Tonicella lokii Clark, 1999, Tonicella marmorea (Fabricius, 1780), Nuttallochiton mirandus (Thiele, 1906), Plaxiphora aurata (Spalowski, 1795)), and one has never been placed in the Mopaliidae (Tonicia chilensis (Frembly, 1827)). The results provide additional evidence that there is high diversity in aesthete canal morphology but also some striking resemblances interpreted here as homologies, reaffirming that aesthete canal characters have considerable potential for phylogenetic analyses and for supporting classification ranks ranging from suborder to species. In this case, the results are broadly consistent with traditional classifications of mopaliids, but Tonicella and Dendrochiton (taxa not always thought not to be mopaliids) share many aesthete canal synapomorphies with undisputed mopaliids, whereas Plaxiphora (typically thought to be a mopaliid) has an aesthete canal system more similar to non-mopaliid members of the Acanthochitonina. These differences are in line with results of recent phylogenetic analyses of the Mopaliidae.