Crustaceans fact sheet | Field of Mars EEC

What are crustaceans?

Crustaceans are invertebrates, which means they do not have a backbone. They belong to a larger group of animals called arthropods. Arthropods have jointed legs, segmented bodies and a hard outer covering called an exoskeleton.

Crustaceans include crabs, prawns, shrimps, lobsters, crayfish, yabbies, barnacles, slaters, pill bugs, beach hoppers, land hoppers and many tiny plankton animals.

Most crustaceans live in water. They can be found in oceans, rock platforms, estuaries, mangroves, rivers, creeks, wetlands and ponds. Some crustaceans, such as slaters, pill bugs and land hoppers, live on land in damp places such as soil, leaf litter, mulch, logs, bark and gardens. Land hoppers are sometimes called lawn prawns.

Crustaceans have a segmented body, jointed legs and a hard outer covering called an exoskeleton.

Soldier crabs are crustaceans found on sandy estuaries, beaches and mangroves.

How do you know it is a crustacean?

Crustaceans are arthropods. Like insects, spiders and myriapods, they have jointed legs, a segmented body and an exoskeleton.

Most crustaceans have two pairs of antennae. This is one way to tell them apart from insects, which have one pair of antennae, and arachnids, which have no antennae.

Many crustaceans have gills and need water or moist places to breathe. Some, such as crabs, prawns and crayfish, live in water or wet places. Land-living crustaceans, such as slaters and pill bugs, hide in damp leaf litter, soil, mulch, bark or under logs and rocks.

Crabs, prawns, yabbies and lobsters are decapods. Decapod means “ten-footed”. These crustaceans have five pairs of walking legs.

Crabs are decapod crustaceans with five pairs of walking legs.

Crustacean groups

Crabs

Crabs are crustaceans with a broad carapace, five pairs of legs and a short abdomen tucked under the body. Many crabs live in oceans, estuaries, mangroves, beaches, rock pools and wetlands.

Soldier crabs live on sandy estuaries and mangroves. They often appear in large groups at low tide and feed by sorting organic matter from wet sand.

Soldier crabs often move across mudflats in large groups at low tide.

Slaters and pill bugs

Slaters and pill bugs are land-living isopod crustaceans. They are not insects. Adult slaters and pill bugs have seven pairs of legs and a segmented body.

They live in damp, sheltered places such as under logs, rocks, bark, pots, mulch and leaf litter. They feed mostly on decaying plant material and help recycle nutrients into the soil.

Slaters are land-living crustaceans that need damp hiding places.

Freshwater crustaceans

Freshwater crustaceans include yabbies, crayfish, freshwater crabs, freshwater shrimps and tiny planktonic species. They live in rivers, creeks, ponds, wetlands and dams.

Freshwater shrimps feed on algae and tiny pieces of organic matter. Yabbies and crayfish feed on plants, dead material and small animals. These animals help move energy through freshwater food webs.

Freshwater shrimps live among aquatic plants and feed on algae and organic particles.

Barnacles and tiny plankton

Barnacles are crustaceans, even though they look like shells attached to rocks, logs, boats or other animals. Young barnacles swim as larvae before settling onto a surface.

Many tiny crustaceans live as plankton in oceans, estuaries and freshwater. These small animals are important food for fish, whales, seabirds and other aquatic animals.

Barnacles are crustaceans that attach to hard surfaces after a swimming larval stage.

What is the life cycle of crustaceans?

Crustaceans hatch from eggs and grow by moulting. Moulting happens because the hard exoskeleton cannot stretch as the animal grows. During a moult, the old exoskeleton splits and the animal comes out with a softer, larger covering that later hardens.

Many aquatic crustaceans hatch as tiny larvae. Crab larvae do not look like adult crabs at first. They drift in the water as plankton before changing into later stages and then young crabs.

Some land-living crustaceans have a simpler life cycle. Female slaters and pill bugs carry eggs in a brood pouch under the body. The young hatch as small pale animals that look like tiny adults and grow through a series of moults.

Many aquatic crustaceans begin life as tiny swimming larvae.

What adaptations do crustaceans have to help them survive?

Crustaceans have many adaptations. A hard exoskeleton helps protect the body. Jointed legs help them walk, swim, dig, climb or hold food. Antennae help them sense touch, smell and movement in their surroundings.

Many crabs have claws for feeding, defence and communication. Some crabs dig burrows or hide under rocks. Freshwater shrimps can flick their tail to move quickly away from danger.

Land-living crustaceans need to avoid drying out. Slaters and pill bugs hide in damp places and are often more active at night. Pill bugs can roll into a tight ball to protect their softer underside.

Pill bugs can roll into a ball to protect their softer underside.

Why are crustaceans important?

Crustaceans are important in healthy ecosystems. Many species recycle dead plants, algae, fungi and animal remains. This helps return nutrients to soil, sediments and water.

Small crustaceans, such as copepods, amphipods and planktonic larvae, are a major food source for fish and other aquatic animals. Larger crustaceans, such as crabs, yabbies and prawns, are eaten by birds, fish, frogs, reptiles, mammals and people.

Crustaceans also help shape habitats. Burrowing crabs can move and aerate sediment. Slaters and pill bugs help break down leaf litter and rotting wood in damp places.

Red-fingered marsh crabs help recycle nutrients as they feed and move through mangrove mud.

How can you help crustaceans?

You can help crustaceans by protecting habitat. Leave leaf litter, logs, bark, rocks and dead wood where it is safe to do so. These places provide damp shelter and food for slaters, pill bugs and land hoppers.

Protect waterways, wetlands, mangroves and estuaries. Keep rubbish, oil, paint, fertiliser and garden chemicals out of drains and creeks because stormwater can carry pollution into aquatic habitats.

Avoid unnecessary pesticide use in gardens and school grounds. Pesticides can harm helpful recyclers as well as pest species.

Clean waterways, wetlands and mangroves help support aquatic crustaceans.

Explore more

Use the fact sheet links on this page to learn more about invertebrates found in bushland, gardens, wetlands, creeks and school grounds.

You can also compare crustaceans with other invertebrate groups such as insects, arachnids, myriapods, worms, molluscs and springtails.

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