Thaumaptilon walcotti, copyright Simon Conway Morris.

Belongs within: Coelenterata.
Contains: Psammocorallia, Cyclozoa, Hyolithellida, Myxozoa, Medusozoa, Tachylasma, Rugosa, Tabulata, Octocorallia, Hexacorallia.

The Cnidaria are an aquatic, mostly marine, group of invertebrates including corals, jellyfish and related taxa. The cnidarian body form is ancestrally radial with a single gut opening surrounded by tentacles; the individual zooid may be sessile (a polyp) or free-living (a medusa). Cnidarians are also characterised by the presence of stinging cells called nematocysts or cnidoblasts. Both these features may be modified to some degree in derived subgroups.

Among living cnidarians, the class Anthozoa has the zooid as a usually sessile polyp that develops directly from a planula (a flattened, bilateral larva). Anthozoan polyps may be solitary or colonial. The Middle Cambrian fossil Thaumaptilon walcotti bears a superficial resemblance to modern colonial anthozoans (particularly pennatulaceans) but may lie outside the cnidarian crown group (Shu et al. 2006). Other possible cnidarians of the early Cambrian include the Hydroconozoa, small, sessile organisms with a cup-like calcareous skeleton.

Conical problematica
Published 15 November 2010

Scattered throughout the fossil record are little mysteries, organisms whose remains have been preserved but which are not obviously relatable to any more familiar group. Either their remains are too simple to preserve much evidence of their affinities, or they are too distinct from other organisms for their affinities to be clear, or both, or some other reason. Unless they are particularly common or otherwise significant, most of these problematica are probably doomed to remain so. Case in point:

The figures above show Asymmetroconus splendidus, described by Korde in 1975 from the Albian (early Cretaceous) of the Crimea. The photos are of thin sections of the fossils; the complete skeleton would have probably been shaped rather like a wine goblet. The largest specimens of Asymmetroconus were just under 8 mm in height. In the same paper, Korde described a number of similar fossils aged from the Albian to the Danian (earliest Palaeocene), assigning them all to the new order Asymmetroconida. Korde attributed the asymmetroconidans to the Hydroconozoa, a group of similar fossils he had himself described previously from the early Cambrian. Hydroconozoa have generally been assigned to the Cnidaria, though their exact position therein remains obscure. Asymmetroconida resembled hydroconozoans in being small and goblet-shaped, with a conical interior to the cup and a basal globular hollow below the point of the cone. However, they differed from Cambrian hydroconozoans in their skeletal microstructure and in the asymmetry of the cup, with one side much thicker than the other. Rozanov & Zhuravlev (1992) later dismissed the idea of Mesozoic hydroconozoans, stating simply that structures described as such had ‘little in common with this group’. No alternative identification of the Asymmetroconida has ever been proposed, and they do not appear to have been properly studied since Korde’s original description.

Reconstruction of the hydroconozoan Hydroconus mirabilis, from Rozanov & Zhuravlev (1992). Whether actually related or not, the Asymmetroconida would have probably looked superficially similar.
Systematics of Cnidaria
<==Cnidaria [Porinae]
    |--Thaumaptilon walcottiSCM06, CM98
    |--Xianguangia sinica Chen & Erdtmann 1991 (see below for synonymy)OH17
    |    |--Gastroconus [Gastroconidae]NS93
    |    |    `--G. venustus Korde 1963NS93
    |    |--Hydroconus [Hydroconidae]NS93
    |    |    `--H. mirabilis Korde 1963NS93
    |    `--Dasyconus [Dasyconidae]NS93
    |         `--D. porosus Korde 1963NS93
       |  `--MedusozoaJ-GP07
       `--Anthozoa [Ceratophyta, Stylophyllicae, Zoantharia]J-GP07
            |  i. s.: Neoclisiophyllum qaidamenseCSZ03
            |         Rylstonia oulongbulukensisCSZ03
            |         DibuniphyllumCSZ03
            |           |--D. bipartitumCSZ03
            |           `--D. vaughaniCSZ03
            |         KueichouphyllumCSZ03
            |           |--K. keishihkuanenseZP86
            |           `--K. sinenseCSZ03
            |         Cystocyathoclisia sinensisCSZ03
            |         Siphonophyllia oppressaCSZ03
            |         Kakwiphyllum qinghaiensisCSZ03
            |         TabulogyraHS02
            |         CalamoserisHS02
            |         CalamophylliopsisHS02
            |         FelixigyraHS02
            |         Embolophyllum aequiseptatumTC71
            |         Tipheophyllum bartrumi [=Eridophyllum bartrumi]F71
            |         Nebulipora ovulum Eichwald 1854 (n. d.)PP05
            |         Cystophrentis kolahoensisZP86
            |         Kueichowpora suniZP86
            |         Pseudouralinia tamgpakouensisZP86
            |         ArachnolasmaZP86
            |           |--A. simplexZP86
            |           `--A. sinenseZP86
            |         AulinaZP86
            |           |--A. carinataZP86
            |           `--A. puerilisZP86
            |         Yuanophyllum kansuenseZP86
            |         Mandulapora permica Ding in Ding, Xia et al. 1984DX84
            |         Zhesipora Ding in Ding, Xia et al. 1984DX84
            |           `--*Z. permica Ding in Ding, Xia et al. 1984DX84
            |         CarinoverbeekiellaDX84
            |           |--C. madreporitea Ding in Ding, Xia et al. 1984DX84
            |           |--C. minor Ding in Ding, Xia et al. 1984DX84
            |           |--C. platiformis Ding in Ding, Xia et al. 1984DX84
            |           `--C. sinensis Ding in Ding, Xia et al. 1984DX84
            |         PseudowaagenophyllumDX84
            |           |--P. elegantulum Ding in Ding, Xia et al. 1984DX84
            |           `--P. vesiculosum Ding in Ding, Xia et al. 1984DX84
            |         DamuqiphyllumDX84
            |           |--D. rotiforme Ding in Ding, Xia et al. 1984DX84
            |           `--D. wumengense Ding in Ding, Xia et al. 1984DX84
            |         Protomichelinia mandulaensis Ding in Ding, Xia et al. 1984DX84
            |         Lophocarinophyllum yakovleviDX84
            |           |--L. y. yakovleviDX84
            |           `--L. y. minutaDX84
            |         TachylasmaDX84
            |         Diphycarinophyllum baotegense Ding in Ding, Xia et al. 1984DX84
            |         PleophyllumDX84
            |           |--P. baytuganenseDX84
            |           |--P. ephippiomorphum Ding in Ding, Xia et al. 1984DX84
            |           |--P. sinense Ding in Ding, Xia et al. 1984DX84
            |           `--P. zhesiense Ding in Ding, Xia et al. 1984DX84
            |         AcanthophyllumF71
            |           |  i. s.: A. mansfieldense (Dun 1898) [=Cyathophyllum mansfieldense]F71
            |           `--A. (Acanthophyllum)F71
            |                |--A. (A.) aequiseptatum Hill 1940F71
            |                `--A. (A.) clermontense (Etheridge 1911) [=Cyathophyllum clermontensis]F71
            |         AmygdalophyllumF71
            |           |--A. etheridgei Dun & Benson 1920F71
            |           |--A. inopinatum (Etheridge 1900) [=Koninckophyllum inopinatum]F71
            |           |--A. minorG31
            |           `--A. obscurumG31
            |         Araeopora australis Nicholson & Etheridge 1879F71
            |         Baeophyllum colligatum Hill 1940F71
            |         Cavanophyllum trochoides (Hill 1940) [=Mictophyllum trochoides]F71
            |         Cionodendron columen Benson & Smith 1923F71
            |         Favistella Hall 1847 [Thecidae]W77
            |           |--F. cerioides Hill 1941F71
            |           |--F. neminghensis (Etheridge 1918) [=Columnaria neminghensis]F71
            |           `--F. stellata Hall 1847 [incl. Columnaria alveolata Edwards & Haime 1851]W77
            |         Gephuropora duni Etheridge 1920 [=Favosites (Columnopora) duni]F71
            |         Conocyathus cyclocostatus Tenison-Woods 1877F71
            |         Conosmilia bicycla Tenison-Woods 1877F71
            |         XystriphyllumF71
            |           |--X. dunstani (Etheridge 1911) [=Cyathophyllum dunstani]F71
            |           |--X. giganteumH79
            |           `--X. mitchelli (Etheridge 1892) [=Cyathophyllum mitchelli]F71
            |         Trapezophyllum elegantulum (Dun 1898) [=Cyathophyllum elegantulum]F71
            |         Zeolasma gemmiforme (Etheridge 1902) [=Diphyphyllum gemmiforme, Disphyllum gemmiforme]F71
            |         Australophyllum cyathophylloides (Etheridge 1911) [=Spongophyllum cyathophylloides]F71
            |         Eddastraea grandis (Dun 1918) [=Phillipsastraea grandis]F71
            |         Sanidophyllum colligatum (Etheridge 1920) [=Endophyllum schluteri var. colligatum]F71
            |         ThamnoporaF71
            |           |--T. marmionensis (Etheridge 1914) [=Favosites marmionensis]F71
            |           |--T. pulchraY92
            |           `--T. wilkinsoni (Etheridge 1891) [=Trachypora wilkinsoni]F71
            |         LyrielasmaF71
            |           |--L. aggregatum (Hill 1940) [=Grypophyllum aggregatum]F71
            |           `--L. subcaespitosum [=Cyathophyllum subcaespitosum]F71
            |         Schedohalysites orthopteroides (Etheridge 1904) [=Halysites orthopteroides]F71
            |         Hercophyllum shearsbyiF71
            |         Phaulactis shearsbyi [=Cyathophyllum shearsbyi, Hercophyllum shearsbyi]F71
            |         Litophyllum konincki [=Amplexopora konincki]F71
            |         MicroplasmaF71
            |           |--M. parallelum Etheridge 1899F71
            |           `--M. trupanonoides (Etheridge 1920) [=Syringopora (Microplasma) trupanonoides]F71
            |         Sterictophyllum creswelli [=Cyathophyllum creswelli, Mictophyllum creswelli]F71
            |         MycophyllumF71
            |           |--M. crateroides (Etheridge 1894) [=Mucophyllum crateroides]F71
            |           `--M. liliiforme (Etheridge 1907) [=Tryplasma liliiformis]F71
            |         Zenophila walli (Etheridge 1892) [=Phillipsastraea walli]F71
            |         RhizophyllumF71
            |           |--R. enorme Etheridge 1903F71
            |           |--R. interpunctatum [incl. R. australe]F71
            |           |--R. robustum Shearsby 1906F71
            |           `--R. yassense Shearsby 1905F71
            |         Sanidophyllum davidis Etheridge 1899F71
            |         Smilotrochus vacuus Tenison-Woods 1877F71
            |         Thamnophyllum curtum Hill 1941F71
            |         Vepresiphyllum falciforme Etheridge 1920F71
            |         TaimyrophyllumN79
            |           |--T. stirpsN79
            |           `--T. triadorumN79
            |         RugosaG02
            |         TabulataG02
            |         Aguayoina Bermúdez 1938LT64
            |           `--*A. asterostomata Bermúdez 1938LT64
            |         Tabulaconus Handfield 1969D78 [TabulaconidaeNS93]
            |           `--T. kordeae Handfield 1969NS93
            |         Prionastraea vaughani Gregory 1899V01
            |         Grypophyllum mackenzienseNU83
            |         Harmodites parallelusG31
            |         PleurophyllumG31
            |           |--P. artienseG31
            |           `--P. tenuiseptatumG31
            |         Phryganophyllum karpinskyiG31
            |         Thysanophyllum tschernowiG31
            |         TetraporaG31
            |           |--T. elegantulaG31
            |           |--T. halysitiformisG31
            |           |--T. laxaG31
            |           |--T. nankinensisG31
            |           `--T. syringoporoidesG31
            |         Monilopora dendroideaG31
            |         Allotropiophyllum sinenseG31
            |         Sinophyllum pendulumG31
            |         Diphiphyllum ultimumG31
            |         ArachnastraeaG31
            |           |--A. coreanicaG31
            |           `--A. manchuricaG31
            |         CystophoraG31
            |           |--C. dubiaG31
            |           |--C. kikkawaiG31
            |           `--C. manchuricaG31
            |         SteinmanniaG31
            |           |--S. geminaG31
            |           `--S. variabilisG31
            |         EuniceaR26
            |           |--E. antipathesR26
            |           `--E. mollisR26
            |         EvactinoporaE89
            |           |--E. crucialisE89
            |           `--E. dendroideaE89
Cnidaria incertae sedis:
  Bellonella rigidaGR98
  ‘Cymodocea’ Lamouroux 1816 non Rafinesque 1814BR05
  Toxorchis kellneriB26
  Erythropodium caribaeorumR96
  ‘Ptolemaia’ McCutcheon & Wilson 1961 non Osborn 1908V66
  Branchiocerianthus imperatorT95
  Planomedusites Sokolov 1972G79
    `--*P. grandis Sokolov 1972G79
  Cosmetira pilodellaD56
  Archotuba Hou et al. 1999C12
    `--A. conoidalis Hou et al. 1999SHB15
  Pteroides griseumPP64
  Sarcodyctyon catenatumPP64
  Thanmostoma cidaritisPP64
  Brachiocerianthus norvegicusPP64
  Eolympia pediculataOH17
  Archisaccophyllia kunmingensisOH17
    |--B. botryoidesG-C96
    `--B. velutinaG-C95
  Eohydiania wenganenseC12
  Sinocyclocylicus guizhouensisC12
  Cambrorhytium Conway Morris & Robison 1988C12
    `--C. fragile (Walcott 1911) [=Selkirkia fragilis]SHB15
  Angela Lesson 1843K18
  Sphenothallus Hall 1847MW04
  Nullipora polymorpha [=Millepora polymorpha]G20

Xianguangia sinica Chen & Erdtmann 1991 [incl. Galeaplumosus abilus Hou et al. 2011, Chengjiangopenna wangii Shu & Conway Morris 2006]OH17

*Type species of generic name indicated


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