Article: Chelodes and closely related Polyplacophora (Mollusca) from the Silurian of Gotland, Sweden
Silicified assemblages of Silurian chitons (polyplacophorans) from Gotland, Sweden are dominated quantitatively by a new, Wenlock species of the long-ranging genus Chelodes; C. actinis sp. nov. is described herein. Head sclerites, previously unknown for Chelodes, are recognized for this species, but no tail sclerites are identified. Other Gotland Chelodes species, including the type species C. bergmani, are revised. Spicuchelodes pilatis, a closely related new genus and species, is also described. Silicification took place by delayed replacement, before significant compaction. Growth patterns of sclerites in the large population of C. actinis demonstrate allometry, and are used as the basis for comparison with those patterns determined from growth lines on individual sclerites of C. gotlandicus and C. cf. bergmani. Variation of individual sclerites interpreted as belonging to a single animal of C. actinis is compared with that in Recent Chiton. Sculpting of the ventral surface in thickened sclerites of these paleoloricate chitons provides evidence for the musculature; this is in contrast to living, neoloricate chitons which rarely show muscle attachment features but have sutural plates to provide physical articulation of sclerites.