Some species of nudibranchs belonging to the genera Felimare and Felimida have spicules in their bodies.
These spicules may have several functions including acting as a deterrent to predators by decreasing the energy value of these animals; they may also have a structural function by increasing stiffness and helping to maintain body shape.
The shape, distribution and density of these spicules in the notum of juvenile forms, which have not yet developed the full potential of their chemical defences, seems to confirm the defensive role of these structures.
As with other animals such as sponges and anthozoans, spicules are capable of strengthening the connective tissue of the animal. A large number of small spicules increase the rigidity of the body and provide a strong inner armour when the animal contracts the body when under attack from a predator.
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