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Marine Molluscs

Marine Molluscs are an extremely diverse group of animals – as shown by the length of the list below! All members of this group have a muscular foot, and most have a hard shell (called a mantle) which can be found either inside or outside of the body.

Common Periwinkle

Common Periwinkle © Katherine Dunsford

Marine Snails and Limpets

This group of molluscs are called Gastropods and have a hard external shell. In the case of sea snails, this is spiralled, although they come in a variety of shapes and sizes. They all have a muscular foot which they use to move and had a hard tongue-like structure (called a radula) which they use to scrape food off surfaces to eat. Limpets scrape out a shallow hole in the rock surface which fits their own shell (called a home-scar), in which they hunker down when the tide goes out. By doing this they keep a small amount of water trapped in their shell which allows them to breathe and prevents them from drying out.

Mussels, Oysters & other Bivalves

Bivalve means paired shell, which is exactly what all animals in this group have. Some bury themselves into the sand, some attach themselves to rocks with strong threads, and some are free-swimming and can ‘swim’ by snapping their shells together! When they are underwater, their shells slightly open allowing them to filter out food particles.

Sea Slugs and Sea Hares

This group on animals is an example of molluscs whose shell is internal or absent completely. Instead they are protected by being poisonous, and to prevent things trying to eat them they are often brightly coloured.

Octopus, Squid & Cuttlefish

The animals in this group are highly developed and are known collectively as Cephalopods. The muscular foot is modified into long tentacles, which they use to catch their prey. Most cephalopods do not have a shell however squid do have a small internal shell. Octopus and cuttlefish can actively change colour to camouflage against their surroundings – handy when wanting to remain unseen when hunting or hiding from predators!


Chitons may often be overlooked when tipping boulders on the rocky shore. Their shell is made up of eight plates, allowing them to secure themselves to uneven surfaces when exposed or to protect themselves from predators.  

Images by Lawson Wood Ocean Eye Films, Jim Greenfield & Katherine Dunsford

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