Mollusca (Molluscs)


Mollusca are comprised by about 120 000 species (80% Gastropoda, 15% Bivalvia) and thus is the second most diverse animal phylum occurring in all major environments except the aerospace. It is also the leading phylum concerning endangered and vulnerable species.

Mollusca is bilateral (or secondarily asymmetrical) Protostomia (Lophotrochozoa). Though quite distinct, their diversity in all aspects of morphology, physiology, behaviour, genetics and ecology is remarkable. Most species are equipped with external spicules or shell (plates) and a foot, a mantle cavity with gills, a ciliary or muscular gliding sole (foot), a visceral portion with heart and excretory organs and alimentary tract with rasping tongue (radula). The body cavity is mesenchymate with a gonopericaridal coelomatic system. Development starts with a spiral cleavage, mostly followed by (often modified) a trochophore‚Äźlike larva. Most freshwater and terrestrial taxa show direct development, however. Both the phylogenetic position of the Mollusca among the Lophotrochozoa and the internal relationships of the eight extant classes still are under debate.

Key Concepts

  • Mollusca is the second most diverse phylum.
  • Gastropoda (limpets, snails, whelks, winkles, slugs) comprise 80%, Bivalvia (mussels, scallops, clams, cockles), about 15% of the diversity of extant Mollusca.
  • There is also a huge body of fossil record throughout all ages.
  • Many continental molluscan species are critically endangered.
  • Mollusca combines a quite strict body plan with tremendous variability in all aspects.
  • The relationships between molluscs and mankind may be positive (food, jewellery and art, research models) or but negative (marine or agricultural pests, vectors of severe diseases).

Keywords: diversity; bauplan; evolution; habits and habitats; phylogeny

Figure 1. The most recent phylogenetic tree based on molecular data showing the relationships of all extant classes (Solenogastres and Caudofoveata are united as Aplacophora) of the Mollusca. Kocot KM, Poustka AJ, Stöger I, Halanych KM, Schrödl M, New data from Monoplacophora and a carefully‐curated dataset resolve molluscan relationships. Scientific Reports 10: 101 (8 pp). Licensed under CC BY 4.0.


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Further Reading

Beesley PL, Ross GJB and Wells A (eds) (1998) Mollusca: The Southern Synthesis. Fauna of Australia, vol. 5, 6A and 6B. CSIRO Publishing: Melbourne.

Harrison FW and Kohn AJ (eds) (1995) Microscopic Anatomy of Invertebrates, vol 5: Mollusca I: Aplacophora, Polyplacophora, Prosobranchia, Opisthobranchia. Wiley‐Liss: New York.

Harrison FW and Kohn AJ (eds) (1997) Microscopic Anatomy of Invertebrates, vols 6A and 6B: Mollusca II: Pulmonata, Monoplacophora, Bivalvia, Scaphopoda, Cephalopoda. Wiley‐Liss: New York.

Ponder WF, Lindberg DR and Ponder JM (2019/2020) Biology and Evolution of the Mollusca, vol. 1–2: 900 + 870 pp. CRC Press, Taylor & Francis Group: Boca Raton, FL.

Wanninger A and Wollesen T (2015) Mollusca. In: Wanninger A (ed.) Evolutionary Developmental Biology of Invertebrates, Lophotrochozoa (Spiralia), vol. 2, pp 103–153. Springer Verlag: Wien.

Wilbur KM (ed.) (1983–1988) The Mollusca, vol. 1–12. Academic Press: Orlando, FL.

Mollia ( includes: (1) a listserver with several hundred malacologists worldwide, (2) the newsletter of UNITAS, the global malacological society, (3) Instructions to authors for many malacological journals.

MolluscaBase (27 editors) ( Taxonomy of all extant and few fossil molluscan taxa with synonyms (a widening of WORMS).

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Haszprunar, Gerhard(Oct 2020) Mollusca (Molluscs). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0029219]