Sealife guideShells, spirals and surprises: the world of marine gastropodsThe marine mollusks

Last updated on 10/16/2025 at 11:50 PM

The class of gastropods includes an immense variety of marine animals, all sharing one key feature: the presence of a univalve shell, a shell made of a single piece, unlike the bivalves, which have two. This shell protects their soft bodies and serves as a shelter they can close when danger approaches.

The flamingo tongue snail (Cyphoma gibbosum) is a gastropod characterized by a single-piece shell.

The flamingo tongue snail is a gastropod characterized by a univalve shell.

Notice the absence of a shell in the pink sea slug !

Spiraled shells

In most gastropods, the shell takes on an elegant spiral shape, a true masterpiece of natural symmetry. This spiral, which may coil to the right or to the left depending on the species, is not only beautiful but also practical: it allows the animal to fit its body inside while maintaining a compact and strong structure.

Amazing exceptions

But nature loves exceptions! Some gastropods have a conical shell rather than a spiral one, while others have lost it entirely. This is the case of the pink sea slug, a small nudibranch with bright colors and delicate shapes. Without a shell, it compensates for its vulnerability through chemical defenses and vivid warning colors, real « don't eat me » signals to would-be predators.

Nudibranchs: jewels of the ocean

Nudibranchs, often called sea slugs, are among the most spectacular gastropods. Their soft, shell-less bodies display extravagant shapes and dazzling colors, ranging from electric blue to translucent pink. These colors don't just please the human eye, they warn predators of their toxicity or bad taste.

Some nudibranchs even have the ability to absorb the toxins or stinging cells of their prey and reuse them for their own defense, a true masterpiece of evolutionary adaptation.

An incredible diversity

From sea snails to sea slugs, marine gastropods inhabit every ocean zone, from rocky shores to the deepest abysses. Their diversity of shapes, sizes and behaviors makes them one of the most fascinating groups in the marine world, a shining example of nature's ingenuity.

Discover marine gastropods

Abe's polycera nudibranch
(Polycera abei)

Brown edge glossodorid
(Glossodoris hikuerensis)

Chamberlain's sea slug
(Nembrotha chamberlaini)

Leech sea slug
(Chelidonura hirundinina)

Little leaf sheep
(Costasiella kuroshimae)

Nudibranch Trapania palmula
(Trapania palmula)

Polka-dot nudibranch
(Jorunna funebris)

Zigzag cowry
(Palmadusta ziczac)

Discover marine mollusks

Broadclub cuttlefish
(Ascarosepion latimanus)

Coconut octopus
(Amphioctopus marginatus)

Curled octopus
(Eledone cirrhosa)

Flamboyant cuttlefish
(Metasepia pfefferi)

Giant rock scallop
(Crassadoma gigantea)

Lined chiton
(Tonicella lineata)

Noble pen shell
(Pinna nobilis)

White-spotted octopus
(Callistoctopus macropus)

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Poisson perroquet à bosse
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