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Temporal range: Upper Ordovician
Scientific classification e
Kingdom: Animalia
Phylum: Mollusca
Class: Polyplacophora
Order: Paleoloricata
Genus: Phthipodochiton
Sutton and Sigwart, 2012[1]
Species: P. thraivensis
Binomial name
Phthipodochiton thraivensis
Sutton and Sigwart, 2012

Phthipodochiton is an extinct genus of molluscs, known from several fossils from the upper Ordovician fauna of the Lady Burn Starfish beds of Girvan, Scotland.[1] It shows a mixture of aplacophoran body plan and polyplacophoran-like valves, and it is an informative fossil in the evolution of aculiferan mollusks.[1]

It was previously classified under the genus Helminthochiton,[2] but it has been reassigned to its own genus in 2012.[1]


Phthipodochiton body is worm-like, with eight polyplacophoran-like valves but no true foot.[3] Head and tail valves are slightly smaller than the intermediate ones.[1] The only ornaments on the valves appear to be growth lines.[1] The body is also covered by a sheet of spicules ; no radula has been preserved.[1]

Life habits[edit]

Phthipodochiton was carnivorous, feeding on crinoids,[3] as shown by a fossil preserved with gut contents.[4] In contrast with modern chitons, Phthipodochiton probably did not creep on its foot but had a locomotion style similar to that of solenogastres.[1]


Phthipodochiton shares similarities with genera as Alastega, Robustum and Septemchiton.[1] but it is sufficiently distinct from all of them to be considered a separate species. It is considered to belong to the aplacophoran stem lineage, along with Acaenoplax,[5] and it has also been placed close to Matthevia and the shelled aplacophoran Kulindroplax in phylogenetic analyses.[6]


  1. ^ a b c d e f g h i Sutton, M. D.; Sigwart, J. D. (2012). "A chiton without a foot". Palaeontology. 55 (2): 401. doi:10.1111/j.1475-4983.2011.01126.x. 
  2. ^ van Belle, R. A. (1981). Catalogue of Fossil Chitons. ISBN 90 6279 018 6. 
  3. ^ a b "Aculifera". Palaeos. Palaeos. Retrieved 21 November 2012. 
  4. ^ Donovan, S. K.; Sutton, M. D.; Sigwart, J. D. (2010). "The last meal of the Late Ordovician mollusc 'Helminthochiton' thraivensis Reed, 1911, from the Lady Burn Starfish Beds, southwest Scotland". Geological Journal: n/a. doi:10.1002/gj.1286. 
  5. ^ Sigwart, J. D.; Sutton, M. D. (Oct 2007). "Deep molluscan phylogeny: synthesis of palaeontological and neontological data". Proceedings of the Royal Society B: Biological Sciences. 274 (1624): 2413–2419. PMC 2274978Freely accessible. PMID 17652065. doi:10.1098/rspb.2007.0701.  For a summary, see "The Mollusca". University of California Museum of Paleontology. Retrieved 2 October 2008. 
  6. ^ Sutton, M. D.; Briggs, D. E. G.; Siveter, D. J.; Siveter, D. J.; Sigwart, J. D. (2012). "A Silurian armoured aplacophoran and implications for molluscan phylogeny". Nature. 490 (7418): 94–97. PMID 23038472. doi:10.1038/nature11328.