Living Things - Invertebrates

Here is some information about a few of the invertebrates (animals without a backbone) that live in Chichester Harbour. Some you might be lucky enough to see but others you will only know they are there by the clues they leave behind.


Shelter and safety: Cockles are molluscs that have a hard outer shell and a soft creature inside. They grow to about 5 cm and have a double shell held together by a hinge. They live buried in clean sand on the seashore just under the surface. At low tide they clamp their shells shut and hide in the sand from birds such as gulls and oystercatchers, which are good at breaking into their shells. They are also eaten by starfish and flatfish. People also like to gather and eat cockles.

Food and water: Cockles feed by drawing water through a tube called a siphon when the tide is in. They strain out small creatures to eat and then expel the water through a second siphon. They have to live near the surface of the mud because their siphon is short.

Growth and reproduction: They release both eggs and sperm into the water and the developing larvae float among the plankton. When they are bigger they settle on the seabed.


Shelter and safety: Crabs live in the sea and can often be found on the seashore, hiding in rock pools and among seaweed. They have a soft body covered by a hard shell which is usually green- brown. They grow to about 9 cm and they have 10 legs. The front two legs are claws, which they use to catch food and fight with. Camouflage colouring and a hard shell help to protect crabs from wading birds that like to eat them. Crabs run sideways, which confuses anything trying to catch them!

Food: Crabs use their claws to catch and eat food. They like to eat meat and will eat almost anything alive or dead! Catching crabs on the end of a line with a piece of bacon has been a favourite children’s pastime for many generations. 

Growth and reproduction: A crab grows by shedding its shell, exposing a new soft one underneath. This takes in water, expands and then hardens. The white ‘dead’ crabs that you find on the seashore are not dead but just the old shell that has been left behind. The eggs are carried in a flap on the underneath of the female and then released into the water where they float as part of the plankton. After about 3 months they sink to the sea bed as tiny crabs.


Shelter and safety: Many people find white, oval cuttlebones on the seashore. However not many people have seen a live cuttlefish. A cuttlefish is related to an octopus. The cuttlebone that you sometimes find is inside the cuttlefish and is covered by the flesh of the creature.

The bone is light and porous and the cuttlefish can fill it with water to make it sink to the seabed so it can hide in the sand. When the cuttlefish empties the bone of water it can float and swim. A cuttlefish is oval, up to 40 cm long and is covered in a zebra stripe pattern, which helps to camouflage it among the eelgrass and seaweed. Its body is surrounded by fins like a skirt, which undulate to help it swim. If it is attacked it can produce a cloud of ink in which to hide. It has large eyes and it can change colour by opening and closing colour cells in its skin, which helps to camouflage it and confuses its prey.

Food and water: It has a tough mouth like a beak to eat crustaceans, especially crabs. It has 10 tentacles around its mouth. Two of these are long with suckers on the end, which it can shoot out to catch prey. It likes to live among eelgrass and seaweed on a sandy or muddy shore so that it can bury itself in the sand or hide in the eelgrass to wait for prey. It can move fast by sucking in water and shooting it out of a funnel that propels it forwards.

Growth and reproduction: It lays clumps of black eggs called ‘sea raisins’ or ‘sea grapes’. They are attached to eelgrass or seaweed.

For more information on marine animals see 'Great British Marine Animals’, Paul Naylor'.

Freshwater shrimps

Shelter and safety: Freshwater shrimps are very common small creatures that live in streams and ponds. Their bodies are flattened and curved with lots of legs. They swim on their sides using their legs. They grow up to 2.5 cm long and are a translucent pale brown colour. They live on the bottom of the pond or stream and among the plants.

Food and water: They eat small bits of plants and dead material and in doing so help to keep the water clean. They locate food by using their long antennae.

Growth and reproduction: The male is larger than the female and they breed very successfully. The female holds the eggs in a brood pouch under her body and the eggs hatch into miniature adults not larvae.


Shelter and safety: Lugworms are reddish brown worms that live on sandy or muddy shores. They grow up to 20 cm long and live in the bottom of a U shaped burrow. They line the walls of their burrows with sticky mucus to stop them collapsing and keep a current of water moving through to provide oxygen. There can be thousands of lugworms in a beach and they hide in their burrows away from wading birds such as redshank, which like to eat them. Fishermen also like to dig them up to use as bait to catch fish.

Food and water: They eat the sand and mud that falls into the top of their burrow and digest the small pieces of plant and other food in it. The waste sand and mud forms worm casts on the beach that we sometimes call ‘sand spaghetti’.

Growth and reproduction: Many lugworms spawn together into the sea at the same time in October and the larvae stay near the seabed where they develop into adults.

Peacock butterfly

Shelter and safety: Peacock butterflies are very colourful with large spots on their wings like those on a peacock’s tail. The spots look like eyes and confuse and frighten birds when they try to catch and eat them.

Food and water: They feed on the nectar of flowers in summer and rotten fruit in the autumn. They lay their eggs on nettles that the caterpillars feed on when they hatch. The caterpillars are black and hairy.

Growth and reproduction: The caterpillars turn into a chrysalis and then hatch into a butterfly. The adult butterflies can hibernate through the winter in a sheltered place such as a shed.


Shelter and safety: Periwinkles are small, dark coloured snails that live on the seashore. They have a rounded spiral shell and are up to 3 cm high. They are very common even though they have been collected for centuries by people to be cooked and eaten.

Their tough shell protects the soft snail inside from being damaged by crashing waves. Their shell also helps protect them from hungry wading birds although there are several birds that are able to crack the shell and eat them.

At low tide they are in danger of drying out so they keep moisture in by closing the entrance of their shell with a horny plate called an operculum, like we would close the door of our house to keep the bad weather out. They can also stick themselves to rocks with a film of mucus.

Food and water: When the tide is in, they feed by scraping seaweed from rocks or eating dead plants. They are able to live in polluted water near sewage works and in marinas.

Growth and reproduction: After mating, the female releases a capsule containing about 9 eggs which hatch and float in the sea. They form part of the plankton before dropping to the seabed and then crawling to the shore.


Shelter and safety: Ragworms are brown worms that live in the mud and grow to about 12 cm long. They are able to swim or crawl through the mud using bristles, which look like legs. They hide in the mud from birds such as curlews that catch and eat them by probing the mud with their long beaks. Fishermen also like to dig them up and use them as bait to catch fish.

Food and water: They live in salt water where it is muddy or sandy. They are active hunters, crawling through the sand and mud to catch and eat small creatures by shooting out their strong jaws.

Growth and reproduction: Many ragworms release sperm and eggs together whilst swimming in the water. The fertilised eggs develop into very small larvae and then drop to the bottom and grow there.

Speckled wood butterfly

Shelter and safety: The speckled wood is a common butterfly of open woodland glades. They can be seen flying in sunny areas and will defend a favourite spot by chasing other butterflies away. Their colours of brown with cream spots camouflage them among the trees. When they rest with their wings together they look like a dead leaf. The eggs hatch into green caterpillars with cream stripes, which look similar to the grass on which they feed. This makes it hard for birds to see and eat them.

Food and water: The caterpillars feed on grass and the butterflies feed on honeydew, which is produced by aphids such as greenfly.

Growth and reproduction: They lay their eggs on the stems of grasses. The caterpillars grow and then turn into a chrysalis. This takes about a month in the summer. Caterpillars that hatch in the autumn stay as caterpillars all winter and then in the spring they turn into butterflies.


Shelter and safety: Sticklebacks are small fish up to 10 cm long with a long thin body and spines along their backs. The nine spined stickleback has nine spines along its back but also one on each fin and one under its tail. The colour of the fish varies but is generally olive green or grey above and bronze or silver below. The spines are not very long so they are not much protection from other fish and birds. However, their colour helps to camouflage them when they hide among the water plants.

Food and water: Sticklebacks usually live in ponds or slow moving freshwater streams but they can also be found in estuaries where the water is salty. They eat other creatures in the stream such as mayfly larvae, worms and freshwater shrimps.

Growth and reproduction: In spring the male stickleback changes colour and becomes marbled grey-green above and black below with white spines. Most fish release eggs and sperm into the water and then do nothing more to care for their young. However the male stickleback builds a nest of plant material stuck together with sticky mucus. He attracts females to lay their eggs in the nest and he fertilises them. When the nest is full, he looks after the eggs and attacks anything that would harm them. He also takes care of the young fish when they hatch.

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Cockle Shell




Crab (photo by George Spraggs)





Cuttlefish (photo by Steve Trewella)




Freshwater Shrimp (photo from Wikimedia)








Peacock Butterfly (photo from Wikimedia)




Periwinkles (photo from Wikimedia)








Speckled Wood Butterfly (photo from Wikimedia)