Polyplacophora

Reconstruction of Gotlandochiton interplicatus, from Smith (1960).

Belongs within: Mollusca.
Contains: Neoloricata.

The Polyplacophora includes the chitons, molluscs in which the test is comprised of a series of separate overlapping valves surrounded by a spicular girdle. Living chitons had eight valves, but varying numbers are found in stem-group chitons. In the Ordovician to Cretaceous Chelodina, the test contained eight generally thick and massive valves that lacked an articulamentum layer at the junction between valves (Smith 1960).

Characters (from Vendrasco et al. 2004): Skeleton with an iterated sequence of overlapping, calcareous, marginally accreted valves, surrounded by an armoured girdle. Anterior and posterior valves differentiated from intervening valves; valve surfaces porous; inner shell layer (articulamentum) projecting from growing margins of valves. Tubular canal systems (in living taxa, housing tissue connecting sensory aesthetes on valve surface to body below) present with valves at interface of two shell layers, with numerous, equally spaced canals branching off obliquely towards surface; vertical canals passing through all shell layers in certain areas.

<==Polyplacophora (see below for synonymy)
    |  i. s.: Arctoplax SB01
    |         Cobcrephora Bischoff 1981 SHC01
    |         Acanthopleurus echinatus (Barne 1842) Y08
    |         Ocruranus EL11
    |         Eohalobia EL11
    |         Lopochites EL11
    |--+--Neoloricata VWR04
    |  `--+--Echinochiton dufoei VWR04
    |     `--+--Rhombichiton DeKoninck 1883 SB12, S60 [=Rhombochiton (l. c.) non Berry 1919 S60]
    |        `--Multiplacophora [Hercolepadida] VWR04
    |             |--Diadeloplax paragrapsima VWR04
    |             |--Protobalanus hamiltonensis VWR04
    |             |--Hercolepas signata VWR04
    |             |--Aenigmatectus VWR04
    |             |--Deltaplax Puchalski et al. 2009 SB12
    |             |--Polysacos Vendrasco, Wood & Runnegar 2004 VWR04
    |             |    `--*P. vickersianum Vendrasco, Wood & Runnegar 2004 VWR04
    |             `--Strobilepis Clarke 1888 VWR04
    |                  `--S. spinigera Clarke 1888 VWR04
    `--Chelodina S60
         |--Chelodes Davidson & King 1874 VWR04, S60 [incl. Sagmaplaxus Oehlert 1881 S60; Chelodidae]
         |    |--*C. bergmani Davidson & King 1874 S60
         |    `--C. calceoloides Etheridge 1897 F71
         |--Gotlandochiton Bergenhayn 1955 [Gotlandochitonidae] S60
         |    |--*G. interplicatus Bergenhayn 1955 S60
         |    |--G. laterodepressus S60
         |    `--G. troedssoni S60
         `--Scanochitonidae S60
              |--Scanochiton Bergenhayn 1943 S60
              |    `--*S. jugatus Bergenhayn 1943 S60
              |--Olingechiton Bergenhayn 1943 S60
              |    `--*O. triangulatus Bergenhayn 1943 S60
              |--Haeggochiton Bergenhayn 1955 S60
              |    `--*H. haeggi Bergenhayn 1955 S60
              `--Ivoechiton Bergenhayn 1955 S60
                   `--*I. levis Bergenhayn 1955 S60

Polyplacophora [Crepipoda, Lamellata, Lepidoglossa, Loricata, Placophora, Polybranchiata, Polyplaciphora, Polyplakiphora, Polyplaxiphora, Polyplaxiphorae]

*Type species of generic name indicated

REFERENCES

[EL11] Erwin, D. H., M. Laflamme, S. M. Tweedt, E. A. Sperling, D. Pisani & K. J. Peterson. 2011. The Cambrian conundrum: early divergence and later ecological success in the early history of animals. Science 334: 1091–1097.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[S60] Smith, A. G. 1960. Amphineura. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I41–I76. Geological Society of America, and University of Kansas Press.

[SB01] Sutton, M. D., D. E. G. Briggs, D. J. Siveter & D. J. Siveter. 2001. An exceptionally preserved vermiform mollusc from the Silurian of England. Nature 410: 461–463.

[SB12] Sutton, M. D., D. E. G. Briggs, D. J. Siveter, D. J. Siveter & J. D. Sigwart. 2012. A Silurian armoured aplacophoran and implications for molluscan phylogeny. Nature 490: 94–97.

[SHC01] Sutton, M. D., L E. Holmer & L Cherns. 2001. Small problematic phosphatic sclerites from the Ordovician of Iapetus. Journal of Paleontology 75 (1): 1–8.

[VWR04] Vendrasco, M. J., T. E. Wood & B. N. Runnegar. 2004. Articulated Palaeozoic fossil with 17 plates greatly expands disparity of early chitons. Nature 429: 288–291.

[Y08] Yu W. 2008. On the genus Yangtzemerisma and related genera (Mollusca: Merismoconchia). Records of the Western Australian Museum 24 (2): 181–194.