Chiton phylogeny (Mollusca Polyplacophora) and the placement of the enigmatic species Choriplax grayi (H. Adams & Angas)

Shallow marine chitons (Mollusca:Polyplacophora:Chitonida) are widespread and well described from established morphoanatomical characters, yet key aspects of polyplacophoran phylogeny have remained unresolved. Several species, including Hemiarthrum setulosum Carpenter in Dall, 1876, and especially the rare and enigmatic Choriplax grayi (Adams & Angas, 1864), defy systematic placement. Choriplax is known from only a handful of specimens and its morphology is a mosaic of key taxonomic features from two different clades. Here, new molecular evidence provides robust support for its correct association with a third different clade: Choriplax is placed in the superfamily Mopalioidea. Hemiarthrum is included in Cryptoplacoidea, as predicted from morphological evidence. Our multigene analysis of standard nuclear and mitochondrial markers demonstrates that the topology of the order Chitonida is divided into four clades, which have also been recovered in previous studies: Mopalioidea is sister to Cryptoplacoidea, forming a clade Acanthochitonina. The family Callochitonidae is sister to Acanthochitonina. Chitonoidea is resolved as the earliest diverging group within Chitonida. Consideration of this unexpected result for Choriplax and our well-supported phylogeny has revealed differing patterns of shell reduction separating the two superfamilies within Acanthochitonina. As in many molluscs, shell reduction as well as the de novo development of key shell features has occurred using different mechanisms, in multiple lineages of chitons.

Reise in den äussersten Norden und Osten Sibiriens, während der Jahre 1843 und 1844 : mit Allerhöchster Genehmigung auf Veranstaltung der Kaiserlichen Akademie der Wissenschaften zu St. Petersburg ausgeführt und in Verbindung mit vielen Gelehrten /

AMNH Library's copy lacks Bd. 1, Th. 2 and Bd. 4, Th. 2, Lief. 3; also lacks plate 1 of atlas (may not have been published)

Reise in den äussersten Norden und Osten Sibiriens während der Jahre 1843 und 1844 mit allerhöchster Genehmigung auf Veranstaltung der Kaiserlichen Akademie der Wissenschaften zu St. Petersburg ausgeführt und in Verbindung mit vielen Gelehrten

I. Bd., Th. I. Einleitung. Klimatologie. Geognosie. Fossile Hölzer. Bearb. von H. R. Göppert. Fossile Mollusken. Bearb. von A. Graf Keyserling. Fossile Fische. Bearb. von J. Müller. 1847. Th.II. Botanik. Bearb. von E. R. v. Trautvetter, F. T. Ruprecht, C. A. Meyer, E. und G. Borszczow. 1856.--II. Bd. Zoologie. Th. I. Wirbellose thiere ... bearb. von F. Brandt, W. F. Erichson, Seb. Fischer, E. Grube, E. Ménétriés, A. Th. v. Middendorff. 1851. Th. II. Säugethiere, vögel und amphibien. Bearb. von A. Th. v. Middendorff. 1853.--III. Bd. Über die Sprache der Jakuten. Th. 1. Lfg. 1. Jakutischer Text. 1848. Th. 2. Lfg. 1. Jakutisch-deutsches Wörterbuch. 1851.--IV. Bd. Übersicht der Natur Nord- und Ost-Sibiriens. Th. 1. Lfg. 1. Einleitung, Geographie und Hydrographie. 1859. Lfg. 1. Atlas. 1859. Lfg. 2. Orographie und Geognosie. 1860. Lfg. 4. Die gewächse Sibiriens. 1864. Th. 2. Lfg. 1.-2. Die Thierwelt Sibiriens. 1867-1874. Lfg. 3. Die eingeborenen Sibiriens. 1875.