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Temporal range: Ediacaran or Cambrian - Recent
Caribbean Reef Squid, Sepioteuthis sepioidea
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Linnaeus, 1758
Cypraea, the Cowrie. About 80% of all known mollusc species are gastropods.

Molluscs, or mollusks, are an important phylum of invertebrate animals. Most of them are marine. They have huge numbers in-shore, that is, in shallow waters near the shore. They are the largest marine phylum, with about 93,000 recognised species, 23% of all named marine organisms. They also occur in freshwater and on land.

Molluscs are extremely varied: they have great diversity. That may be why there is no word in English for the phylum as a whole. "In an evolutionary sense, molluscs are plastic material".[1]

Most molluscs have shells, but some groups do not: octopods, slugs, and the gastropods known as sea slugs. There is great variety in the phylum, much more so than their ancient rivals, the brachiopods.[2]


Classes of molluscs:


It has become clear that the fossil taxon Helcionelloida does not belong to the class Gastropoda. It is now a separate class in the Mollusca. Parkhaev (2006, 2007) created the class Helcionelloida, whose members were previously treated as "Paleozoic molluscs of uncertain systematic position" by Bouchet & Rocroi.[3][4]



  1. Morton J.E. 1958. Molluscs. London: Hutchinson University Library, p11.
  2. Barnes, Robert D. 1982. Invertebrate zoology. Philadelphia PA: Holt-Saunders. ISBN 0-03-056747-5.
  3. P. Yu. Parkhaev (2006) "Adaptive radiation of the Cambrian helcionelloid mollusks (Gastropoda, Archaeobranchia)." In: S.V. Rozhnov (ed.) "Evolution of the biosphere and biodiversity. Towards the 70th anniversary of A. Y. Rozanov". 2006. Moscow, pp. 282-296.
  4. P. Yu. Parkhaev (2007). "The Cambrian 'basement' of gastropod evolution". Geological Society, London, Special Publications 286: 415–421. doi:10.1144/SP286.31 . ISBN 978-1-86239-233-5 .