Phthipodochiton

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]

Phthipodochiton
Temporal range: Upper Ordovician
Scientific classification
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

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

Morphology

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

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]

Taxonomy

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]

References
  1. 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. "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" (PDF). 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. doi:10.1098/rspb.2007.0701. PMC 2274978. PMID 17652065. 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. doi:10.1038/nature11328. PMID 23038472.
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