By far the great majority of animals on earth are invertebrates; animals without a backbone. They make up about 95% of all known species .Marine invertebrates are particularly interesting having adapted to an aquatic lifestyle. At Burntcoat Head the best time to see marine invertebrates is at low tide and the best place is at the water’s edge. Here the tide pools can sustain the shorelife during the time it takes the tide to return. At low tide a myriad of life is exposed on the ocean floor, which makes exploration very interesting.

Who’s Who on the Ocean Floor


You will see many different types of molluscs. Most molluscs are aquatic and have shells protecting their soft bodies. Major groups include bivalves and gastropods.

  • Bivalves This term is used to describe molluscs which have two shell parts hinged together protecting the soft body inside. Mussels, clams, scallops and oysters are all bivalves.
  • Gastropods This group of molluscs have a single shell covering, usually formed in a coil or whorl. The shell has a lid which can open and close. It opens when feeding and closes to provide protection for the animal’s body inside. Gastropods include periwinkles, whelks, snails, and limpets


Crabs are crustaceans. They have hard exoskeletons which moult as they grow. Look for the Hermit crab, instead of growing its own shell, the Hermit crab finds shells of other species such as moon snails in which to take up residence. As the crab grows, it exchanges its outgrown shell for a larger one. All crabs are decapods, they have ten legs. The first pair are modified into claws.


These are encrusters; they attach themselves permanently to a variety of surfaces and thereafter don’t move. Surfaces include bedrock, boulders, pebbles and shells. They will also attach themselves to man made objects such as docks and the hulls of various sizes of water craft.

Barnacles are sessile, they don’t move about they cluster together in groups.

Sponges are animals, not plants.

As you explore the shoreline you may find pieces or clumps of mermaid’s gloves or deadman’s fingers which have washed up on shore. These pieces look like seaweed but are not. They belong in the group of marine invertebrates commonly referred to as demosponges.


Bryozoans are similar to sponges in that they look like plants but are not. They are often referred to as the moss animals. These are very different aquatic animals. They form colonies composed of tiny little individuals (zooids) who have hooked up together forming a variety of shapes and sizes. Locally we have the leafy bryozoan.