Crustaceans are mainly water-dwelling animals with a hard, segmented exterior body known as an exoskeleton. Crustaceans are a member of the arthropod family, and there are roughly 67,000 recorded species of Crustacea on the planet. All crustaceans are made up of three major body parts: The head, thorax, and abdomen. In addition, crustaceans have two sets of antennae, and most breathe through gills, although some crabs have developed lungs to live on land.
What are arthropods?
Arthropods are invertebrates that have segmented bodies and paired, joined appendages. Arthropods are typically split into Arachnids, crustaceans, Hexapoda (insects and springtails), and Myriapoda (millipedes and centipedes). Arthropods got their name from the root Latin word Arthropoda, which means ‘those with jointed feet.’ Around 800,000 recorded species of arthropods can be found in all areas of the world.
Types of aquatic crustaceans
Many aquatic crustaceans can be found in rivers, lakes, and oceans. But here are a few of the most well-known crustaceans which you can discuss in your classroom:
Lobsters live in the sea and are often found on the seabed (lobsters can swim but mostly walk along the seabed). They live in crevasses or borrows and mostly come out at night to hunt and feed. Lobsters are typically dark blue/green to help them blend in with their environments; it’s not until they are cooked that they get their pink color. Lobsters never stop growing in their natural habitat and continue until they die – the largest lobster ever recorded was a whopping 20 kg. However, once a lobster is caught, it will stop growing.
Crabs can live in the sea, freshwater, and land. Crabs can vary in size from the tiny pea crab, which is only a few millimeters wide, to the Japanese spider crab, which can have a leg span of 13ft! Crabs are omnivores that mostly eat algae but also hunt and eat worms, mollusks, and other crustaceans. There are roughly 4,500 species of crab, and it can be found worldwide from shallow waters to deep seas, to polar waters to the tropics. In addition, there are about 450 species of crab have evolved to live in freshwater and on land.
Prawns have ten legs, long antennae, and two bulbous black eyes that sit on stalks. These eyes are compound eyes that give prawns a panoramic view to detect movement. Prawns can be found in all habitats, including the sea floor, freshwater lakes, and rivers. Although prawns can vary from 2 cm to 25 cm, these large prawns are often targeted for human consumption.
Barnacles are exclusively marine crustaceans and can be found in shallow and tidal waters with a lot of activity. They attach themselves to various things, such as the bottom of boats, rocks, eroding sea infrastructure, and other creatures. They secrete a fast-setting cement, allowing them to stick to things quickly. The glue is so powerful that scientists are trying to discover how to use it commercially. Barnacles feed by pushing out an appendage called cirri. It sweeps the area for microscopic organisms and withdraws back into their protective shell. Barnacles main predators are whelks, snails, and starfish.
Most crustaceans are aquatic; however, as mentioned above, some crabs have evolved to live on land and water. The only crustacean that has come to live exclusively on land is the woodlouse. Woodlice can be found in cool, damp habitats such as rotting vegetation and wood. The woodlice don’t breathe using lungs; it has gills covered in a thin layer of water to allow them to breathe properly – which is why woodlice prefer damp, moist environments. Woodlice eat rotting plants and fungi and are eaten by spiders, toads, shrews, and centipedes.
Crustaceans in the food chain
Most crustaceans are scavengers; they eat scraps and dead creatures on sea beds and at the bottom of lakes and rivers. Crabs, shrimp, and prawns often search for food and night and hide in enclosed crevasses during the day. Most scientists thought lobsters were also scavengers. However, they have since been discovered to be predators/ are predators. They use their powerful claws to catch prey and eat fish, clams, mussels, and sometimes other lobsters!
Crustaceans are an important food source for a whole host of other animals. Eels and some fish equipped to deal with crustacean’s tough outer shells, like pufferfish and triggerfish, eat crustaceans. Octopuses, seals, turtles, and rays all hunt and eat crustaceans in the sea, and they are also under threat from land animals too! Monkeys, rats, and raccoons all hunt for crustaceans whenever possible. And, of course, they are a big part of the human food chain. Roughly 10 million tons of crustaceans are produced yearly from farming and fishing for human consumption.
How do crustaceans grow?
Crustaceans replace their exoskeletons with new ones to grow – this is a process called molting. Crustaceans molt away their old exoskeleton and wait for a new one to be formed. However, crustaceans are vulnerable to predators while their new exoskeleton is hardening, and they can’t defend themselves. Most crustaceans molt around 15 – 25 times to reach their full size. But, apart from lobsters, as we have already learned, they can keep growing.
How do crustaceans reproduce?
Most crustaceans reproduce sexually with a male and a female. Most female crustaceans lay eggs that hatch into swimming larvae, but prawn eggs hatch into small versions of themselves. Barnacles are hermaphrodites, so they can produce their sperm and eggs to reproduce. Some crustaceans use visual stimulus to attract mates; crabs use their claws to ‘wave’ at their chosen potential mating partner. Others attract their mates using pheromones; a female lobster will waft pheromone-laced urine into a male lobster’s dwelling; if he likes the scent, he will let her in!
There are lots of Australian crustaceans which dwell in and around Australia. Most are different species of lobster and prawn but are native to Australia and its surrounding waters. Here are a few Australian Crustaceans which you might have heard of:
These Australian freshwater crayfish are found in streams, billabongs, and lakes and are popular to eat in Australia; they provide an alternative to prawn, crab, and lobster. They can survive in dry conditions during droughts by burrowing deep in muddy creeks and river beds and lying dormant.
The Ibacus peronii is more commonly known as the Balmain bug and is a type of lobster. These can be found in shallow waters around the coast of Australia. These crustaceans have broad, flat bodies and can reach lengths of up to 23 cm and widths between 10 – 14 cm. Although these are nocturnal creatures who eat algae and other crustaceans, they spend most of the daytime under sand or mud.
Giant freshwater prawn
These can be found in northern Australia and are commonly known as cherabin in Australia. These can also be found in India and Southeast Asia. Cherabin can grow up to 30 cm in length and feature a front pair of elongated legs used as feeding appendages. They are often dark brown, but some vary in color, and others display faint vertical stripes.