Belongs within: Sachitida.
Contains: Chelodina, Neoloricata, Solenogastres, Caudofoveata.
The Aculifera are an assemblage of molluscs with an external mantle stiffened by spicules or scales. The Polyplacophora, chitons, have a dorsal shell comprised of a series of separate overlapping valves surrounded by a spicular girdle. In modern Aplacophora, the shell is entirely absent but a similarly valvular shell has been identified in fossil representatives (Sutton et al. 2012). Eight valves are present in living chitons and shelled aplacophorans, but varying numbers are found in some stem-group chitons.
Characters (Smith 1960, as Amphineura): Aquatic, marine, bilaterally symmetrical mollusks having external mantle bearing series of exposed dorsal or, less commonly, internal calcareous plates, or stiffened by disseminated calcareous spicules. Head partially or not differentiated in form; body oval, elongate, or flattened; foot expanded and developed for creeping or wormlike, with a ventral groove or none. Nervous system consisting of esophageal ring with ganglia and four longitudinal cords, two ventral and two lateral; no cephalic eyes, tentacles or otocysts. Gills paired or many, posterior or lateral; mouth anterior, usually with radula; anus posterior and median.
Aculifera [Chelodida, Eoplacophora, Mattheva, Mattheviidae, Matthevina, Paleoloricata]SB12
| i. s.: SpicuchelodesJB12
| Preacanthochiton [Preacanthochitonidae]BE93
| |--P. cooperi Bergenhayn 1960BE93
| |--P. depressus Bergenhayn 1960BE93
| `--P. productus Bergenhayn 1960BE93
| HemithecellaCRF04
| ConodiaCRF04
| CalceochitonCRF04
|--Polyplacophora (see below for synonymy)SB12
| | i. s.: ArctoplaxSB01
| | Cobcrephora Bischoff 1981 [Cobcrephoridae, Phosphatoloricata, Phosphatoloricatida]SHC01
| | |--C. corrugataBRW98
| | `--C. silurica Bischoff 1981BE93
| | Acanthopleurus echinatus (Barne 1842)Y08
| | Ocruranus Liu 1979BR17
| | |--O. finialP08
| | `--O. trulliformisP08
| | Eohalobia diandongensisEL11, P08
| | Sinuconus Yu 1979 [Sinuconidae]BR17
| | `--*S. clypeus Yu 1979BR17
| |--ChelodinaVWR04
| `--+--NeoloricataVWR04
| `--+--Echinochiton dufoeiVWR04
| `--+--Rhombichiton DeKoninck 1883SB12, S60 [=Rhombochiton (l. c.) non Berry 1919S60]
| `--Multiplacophora [Hercolepadida]VWR04
| | i. s.: Diadeloplax paragrapsimaVWR04
| | AenigmatectusVWR04
| | Deltaplax Puchalski et al. 2009SB12
| | Polysacos Vendrasco, Wood & Runnegar 2004VWR04
| | `--*P. vickersianum Vendrasco, Wood & Runnegar 2004VWR04
| | Strobilepis Clarke 1888VWR04
| | `--S. spinigera Clarke 1888VWR04
| `--HercolepadidaeWS93
| |--Hercolepas signata (Aurivillius 1892)VWR04, WS93
| `--ProtobalanusWS93
| |--P. hamiltonensis Hall & Clarke 1888WS93
| `--P. spinicoronatusVP17
`--Aplacophora [Scolecomorpha, Telobranchia]SB12
| i. s.: Crystallophrisson nitensI96
|--SolenogastresSB12
|--RobustumSB12
|--AcutichitonidaeBE93
| |--Acutichiton etheridgei Smith & Hoare 1987SB12, BE93
| |--Elachychiton juxtaterminus Hoare & Mapes 1985BE93
| `--SoleachitonBE93
| |--S. soleaformis (Etheridge 1882)BE93
| `--S. yochelsoni Hoare & Smith 1984BE93
|--Septemchitonidae [Septemchitonida, Septemchitonina]BE93
| |--+--Bursata santacrucensis Dzik 1994D94
| | `--Solenocaris Young & Young 1868D94, S60
| | |--*S. solenoides Young & Young 1868S60
| | `--S. elongata (Hadding 1913)BE93
| `--+--Sarkachiton kielcensis Dzik 1994D94
| |--Carnicoleus gazdzickii Dzik 1986D94
| `--Septemchiton Bergenhayn 1955SB12, S60
| |--*S. vermiformis Bergenhayn 1955S60
| |--S. grayiae (Woodward 1885)BE93
| `--S. thraivensis (Reed 1911)BE93
`--+--+--CaudofoveataSB12
| `--GenitoconiaVP17
`--+--Phthipodochiton thraivensis [=Helminthochiton thraivensis]SB12
`--+--Kulindroplax Sutton, Briggs et al. 2012SB12
| `--*K. perissokomos Sutton, Briggs et al. 2012SB12
`--+--Matthevia Walcott 1885SB12, S60
| |--*M. variabilis Walcott 1885F62
| |--M. wahwahensisVP17
| `--M. walcotti Runnegar et al. 1979BE93
`--+--EnetoplaxSB12
|--HeloplaxSB12
`--Acaenoplax Sutton, Briggs et al. 2001SB12, SB01
`--*A. hayae Sutton, Briggs et al. 2001SB01
Polyplacophora [Crepipoda, Lamellata, Lepidoglossa, Loricata, Placophora, Polybranchiata, Polyplaciphora, Polyplakiphora, Polyplaxiphora, Polyplaxiphorae]SB12
*Type species of generic name indicated
References
[BRW98] Beesley, P. L., G. J. B. Ross & A. Wells (eds) 1998. Fauna of Australia vol. 5. Mollusca: The Southern Synthesis. Part A. Australian Biological Resources Study: Canberra.
[BE93] Benton, M. J., & D. H. Erwin. 1993. Mollusca: Amphineura and ‘Monoplacophora’. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 125–130. Chapman & Hall: London.
[BR17] Bouchet, P., J.-P. Rocroi, B. Hausdorf, A. Kaim, Y. Kano, A. Nützel, P. Parkhaev, M. Schrödl & E. E. Strong. 2017. Revised classification, nomenclator and typification of gastropod and monoplacophoran families. Malacologia 61 (1–2): 1–526.
[CRF04] Cherns, L., D. M. Rohr & J. Frýda. 2004. Polyplacophoran and symmetrical univalve mollusks. In: Webby, B. D., F. Paris, M. L. Droser & I. G. Percival (eds) The Great Ordovician Biodiversification Event pp. 179–183. Columbia University Press.
[D94] Dzik, J. 1994. Evolution of ‘small shelly fossils’ assemblages of the early Paleozoic. Acta Palaeontologica Polonica 39 (3): 247–313.
[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.
[F62] Fisher, D. W. 1962. Small conoidal shells of uncertain affinities. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W98–W143. Geological Society of America, and University of Kansas Press.
[I96] Ivanov, D. L. 1996. Origin of Aculifera and problems of monophyly of higher taxa in molluscs. In: Taylor, J. D. (ed.) Origin and Evolutionary Radiation of the Mollusca pp. 59–65. Oxford University Press: Oxford.
[JB12] Johnson, M. E., & B. G. Baarli. 2012. Development of intertidal biotas through Phanerozoic time. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 63–128. Springer.
[P08] Parkhaev, P. Y. 2008. The Early Cambrian radiation of Mollusca. In: Ponder, W. F., & D. R. Lindberg (eds) Phylogeny and Evolution of the Mollusca pp. 33–69. University of California Press: Berkeley.
[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.
[VP17] Vinther, J., L. Parry, D. E. G. Briggs & P. Van Roy. 2017. Ancestral morphology of crown-group molluscs revealed by a new Ordovician stem aculiferan. Nature 542: 471–474.
[WS93] Wills, M. A., & J. J. Sepkoski Jr. 1993. Problematica. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 543–554. Chapman & Hall: London.
[Y08] Yu W. 2008. On the genus Yangtzemerisma and related genera (Mollusca: Merismoconchia). Records of the Western Australian Museum 24 (2): 181–194.