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Cirrate shell
Internal shell of cirrate octopuses

Cirrate octopuses possess a well-developed internal shell that supports their muscular swimming fins. This is in contrast to the more familiar, finless, incirrate octopuses, in which the shell remnant is either present as a pair of stylets or absent altogether.

The cirrate shell is quite unlike that of any other living cephalopod group and has its own dedicated set of descriptive terms. It is usually roughly arch- or saddle-shaped and is rather soft, being similar in consistency to cartilage. Each of the eight extant cirrate genera is characterised by a distinct shell morphology outlined below (below taxonomy updated per WoRMS):

The comparatively simple shells of Opisthoteuthidae and Stauroteuthidae are thought to approximate the ancestral shape, with those of Cirroteuthidae being more derived. The shell of Cirroctopus appears transitional in form between those of incirrate octopuses and other cirrates, and resembles the reduced shell of the Late Cretaceous Palaeoctopus newboldi. The paired, rod-shaped stylets of incirrates are evolutionarily derived from the lateral wings and horns of the cirrate shell.

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Further reading

  • Bizikov, V.A. (2004). The shell in Vampyropoda (Cephalopoda): morphology, functional role and evolution. Ruthenica 3: 1–88.
  • Haas, W. (2002). The evolutionary history of the eight-armed Coleoidea. Abhandlungen der Geologischen Bundesanstalt, Wien 57: 341–351.

References

  1. Fuchs, D., C. Ifrim & W. Stinnesbeck (2008). A new Palaeoctopus (Cephalopoda: Coleoidea) from the Late Cretaceous of Vallecillo, north-eastern Mexico, and implications for the evolution of Octopoda. Palaeontology 51(5): 1129–1139. doi:10.1111/j.1475-4983.2008.00797.x /wiki/Doi_(identifier) ↩

  2. Young, R.E., M. Vecchione & K.M. Mangold (1999). Cephalopoda Glossary. Tree of Life Web Project. http://tolweb.org/accessory/Cephalopoda_Glossary?acc_id=587 ↩

  3. Young, R.E., M. Vecchione & K.M. Mangold (2002). Cirrate Shell Terminology. Tree of Life Web Project. http://tolweb.org/accessory/Cirrate_Shell_Terminology?acc_id=1488 ↩

  4. Vecchione, M., K.M. Mangold & R.E. Young (2010). Cirrata Grimpe, 1916. Tree of Life Web Project. http://tolweb.org/Cirrata/20086 ↩

  5. Collins, M.A. & R. Villanueva (2006). Taxonomy, ecology and behaviour of the cirrate octopods. In: Gibson, R.N., R.J.A. Atkinson & J.D.M. Gordon (eds.) Oceanography and Marine Biology: An Annual Review. Aberdeen University Press, Aberdeen. pp. 277–322. https://books.google.com/books?hl=en&lr=&id=R7-TfdYeLEgC&oi=fnd&pg=PA277 ↩

  6. Villanueva, R., R.E. Young & M. Vecchione (2008). Opisthoteuthis Verrill 1883. Tree of Life Web Project. http://tolweb.org/Opisthoteuthis/20106 ↩

  7. Verhoeff, Tristan Joseph; O’Shea, Steve (2022-01-02). "New records and two new species of Grimpoteuthis (Octopoda: Cirrata: Grimpoteuthididae) from southern Australia and New Zealand". Molluscan Research. 42 (1): 4–30. doi:10.1080/13235818.2022.2035889. ISSN 1323-5818. https://www.tandfonline.com/doi/full/10.1080/13235818.2022.2035889 ↩

  8. Collins, M., R. Villanueva & R.E. Young (2008). Cryptoteuthis Collins, 2004. Tree of Life Web Project. http://tolweb.org/Cryptoteuthis_brevibracchiata/121985 ↩

  9. Bizikov, V.A. (2004). Evolution of shell in Octopodiformes (Cephalopoda) Archived 2013-10-21 at the Wayback Machine. In: Abstracts of the conference Mollusks of the Northeastern Asia and Northern Pacific: Biodiversity, Ecology, Biogeography and Faunal History. October 4–6, 2004, Vladivostok, Russia. pp. 21–23. http://rfems.dvo.ru/conference_2004/Malacological_Conference_2004_-_Abstracts.pdf#page=22 ↩

  10. Bizikov, V.A. (2004). Evolution of shell in Octopodiformes (Cephalopoda) Archived 2013-10-21 at the Wayback Machine. In: Abstracts of the conference Mollusks of the Northeastern Asia and Northern Pacific: Biodiversity, Ecology, Biogeography and Faunal History. October 4–6, 2004, Vladivostok, Russia. pp. 21–23. http://rfems.dvo.ru/conference_2004/Malacological_Conference_2004_-_Abstracts.pdf#page=22 ↩

  11. Bizikov, V.A. (2004). Evolution of shell in Octopodiformes (Cephalopoda) Archived 2013-10-21 at the Wayback Machine. In: Abstracts of the conference Mollusks of the Northeastern Asia and Northern Pacific: Biodiversity, Ecology, Biogeography and Faunal History. October 4–6, 2004, Vladivostok, Russia. pp. 21–23. http://rfems.dvo.ru/conference_2004/Malacological_Conference_2004_-_Abstracts.pdf#page=22 ↩