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Ophiocistioidea is a class of extinct echinoderms from the Palaeozoic and early Mesozoic.[2] They most likely form a paraphyletic grade along sea cucumber stem lineage,[3] although some sources still consider the question of ophiocistioid monophyly unresolved.[4]

Etymology

Ophiocistioidea is named from the Greek words ὄφις (ophis) “snake” and κίστη (kiste) “box”.[5]

Anatomy

Sollasina cthulhu

Ophiocistioids had a flattened globular body encased in a solid test of calcareous plates, similar to that of a modern sea urchin. As with sea urchins, the mouth faced downwards and contains a structure known as an Aristotle’s lantern. Unlike sea urchins, the anus was laterally placed rather than being at the center of the upper surface. Five ambulacra radiated outwards from the mouth across the lower surface, but only continued around the edge to just under the level of the anus. The madreporite was to one side of the mouth.[6] Ophiocistioids had unusually long tube feet emerging from near the mouth and around the edges of the body. Unlike the tube feet of other echinoderms, these tube feet were covered in stereom plates.[7]

Phylogeny

The skeletal structure, close to that of sea urchins (and sea cucumbers for some soft species[8]), often places these animals in Echinozoa.[9] However, the data are still insufficient to finally decide on this case:[10] the study of particularly well-preserved fossils suggests that Ophiocistioidea could be the ancestor group of sea cucumbers.[11]

At present, about 40 species have been identified[9] (10 are from the Devonian, which seems to be the golden age of this group[9]), categorized into 17 genera and 6 families. Most of the fossils have been found in North America and Europe, with some in Australia.[10]

List of families and genera from Reich & Haude (2004)[9]

See also

References

  1. ^ Reich & Haude 2004 harvnb error: multiple targets (2×): CITEREFReichHaude2004 (help)
  2. ^ a b Reich et al. 2018
  3. ^ Rahman et al. 2019, pp. 4–6
  4. ^ Nanglu et al. 2023, p. 331
  5. ^ Ubaghs 1966
  6. ^ Smith & Reich 2013, pp. 677–678
  7. ^ Rahman et al. 2019, pp. 2–4
  8. ^ Haude, R. (2004). “Mode of life of ophiocistioids (Echinozoa) according to plated and “naked” forms in the Rhenish Devonian”. Echinoderms: Munchen, Proceedings of the 11th International Echinoderm Conference. pp. 409–416. doi:10.1201/9780203970881.ch67..
  9. ^ a b c d Reich, M.; Haude, R. (2004). “Ophiocistioidea (fossil Echinodermata): an overview” (PDF). Echinoderms: Munchen..
  10. ^ a b Cite error: The named reference Mah was invoked but never defined (see the help page).
  11. ^ “A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan”. Proceedings of the Royal Society B. 2019. doi:10.1098/rspb.2018.2792. {{cite web}}: Unknown parameter |auteurs= ignored (help).

Works cited