Lobsters, rock lobsters and crayfish
Article | Updated 6 months ago
Lobsters, rock lobsters and crayfish may look similar and can be easily confused. Do you have the keys to distinguish them? Here are some photos of crustaceans. Would you be able to recognise each species?
A family story
Lobsters, crayfish and rock lobsters are all aquatic arthropods. Their external skeleton and segmented body classifies them into the group of crustaceans. Despite the fact they have very similar appearances, lobsters, rock lobsters and crayfish do not belong to the same family. To understand their taxonomic differences, take a look at this classification.
|Family||Palinuridae||Nephropidae||Cambaridae, Astacidae, Parastacidae|
Lobsters, sometimes named “true” lobsters, belong to the family Nephropidae whereas rock lobsters belong to Palinuridae. Moreover, there are three families of crayfish: Cambaridae, Astacidae, Parastacidae, also different from the two previous families.
Lobsters, rock lobsters and crayfish are not closely related. Moreover, rock lobsters are sometimes mistakenly called “crayfish” in Australia, New Zealand and South Africa, but they are neither lobsters nor crayfish. Common names are often confusing!
Different diets due to a different anatomy
Like prawns, shrimps and crabs, lobsters, rock lobsters and crayfish belong to the order Decapoda and have five pairs of legs on the main part of the body and five pairs of swimmerets. In lobsters and crayfish, the pair of legs closest to the head is differentiated into two claws. There are no claws in rock lobsters and that is the first major difference.
Lobsters have enormous, unequal and specialised claws which help them to defend themselves, attack, and catch prey. Their sharp cutter claw enables lobsters to tear their prey whereas the crusher claw, which is larger and dented, is used for crushing the food up. Their two potent claws allow these predators to eat a lot of different prey such as small fish, sea urchins, crabs and sea stars. When lobsters lose a claw, a new one grows up with the next moult. However, if they lose a crusher claw, the most important one because it allows lobsters to access their food, the cutter claw transforms into a crusher claw and a cutter claw will grow up with the next moult.
Devoid of claws, rock lobsters developed other arms to aide defence, such as sharp thorns all over their body and two horns on their head. Furthermore, when they feel endangered rock lobsters produce a loud defence screech rubbing one of their long antennae against a soft part of their carapace. Not adapted for efficient hunting and unable to cut their prey, rock lobsters feed on small animals such as snails, clams, crabs, small shells and sea urchins, and also may scavenge.
Like “true” lobsters and contrary to rock lobsters, crayfish have a smooth carapace and a large pair of claws, used to crush and tear food. They feed on aquatic plants, insects, worms and molluscs, and may also scavenge. Crayfish also have two pairs of legs ending in pincers and two pairs of simple walking legs.
A divergent ecology
Lobsters are marine animals living in cold oceans and seas. The genus Homarus includes only two species: the European or Breton lobster (H. gammarus), occurring all around Europe, and the American lobster (H. americanus), found on the Atlantic coast of North America, from Canada to North Carolina. Thus, there are no lobsters on the Australian coastline! Their exoskeleton’s colour depends on their natural environment to act as a camouflage and prevent them from being seen by predators. In deep European water lobsters are blue while American lobsters are brown or green.
Rock lobsters, also known as spiny lobsters, are sometimes brown, red or very colourful and live in coral reefs and in crevices of rocks in tropical areas. They occur in hot waters in the Pacific, Atlantic and Indian oceans and also in Red and Mediterranean seas. In Australia the Southern Rock lobster, caught in south-eastern Australia, and the Western Rock lobster, found in southern Western Australia, are two species of particular commercial value.
Contrary to lobsters and rock lobsters, crayfish are freshwater crustaceans that inhabit rivers, lakes, dams, streams and ponds. A huge diversity of crayfish is found in North America but the different species of crayfish occur all around the world. Australia even houses the largest freshwater invertebrate in the world: the Tasmanian giant freshwater crayfish (Astacopsis gouldi). This species is endemic of Tasmania and listed as an endangered species due to over fishing and human activity destroying its habitat. In the past, it was possible to find specimens weighing up to 5kg in the northern rivers of Tasmania. Nowadays, specimens over 2kg are rare.
Two characteristics to recognise them
What did you catch? You come back from fishing and you don't know if you have a rock lobster, a crayfish or a lobster in your basket. In the wild, two easy characteristics may help you to recognise them: the claws and type of water where the animal lives.
- You caught it in salt water and it has no claws… It is a rock lobster
- You caught it in salt water and it has claws… It is a lobster
- You caught it in freshwater and it has claws… It is a crayfish.
Caution, it might be another crustacean!
With 67,000 recorded species, the Crustacean group includes many arthropods that share physical features, such as lobsters, rock lobsters and crayfish, but also blind lobsters, reef lobsters, slipper lobsters, scampi and squat lobsters, to name a few!
Slipper lobsters are easily recognisable by their enlarged plate-like antenna attached in front of the eyes. Despite their name, they are more closely related to rock lobsters than “true” lobsters and live in warm oceans. “Slipper lobster” is not the name of a species but the common name for the crustacean family Scyllaridae which includes 22 genera and many more species. That explains why so many alternative names are assigned to slipper lobsters! Sometimes known as Shovel-nosed lobsters, Spanish lobsters, Mitten lobsters or Fan lobsters. Slipper lobsters are also called “Bugs” in Australia.
Another lobster-like creature is the Scampi, also known as the Norwegian Lobster or Dublin Bay Prawn, belonging to the family Nephropidae, like “true” lobsters. They are abundant in Europe in the north-eastern Atlantic Ocean and North Sea but relatively rare and expensive in Australia. Such as many cold-water lobsters, scampi often host commensal animals on their exoskeleton which benefits without affecting the scampi. The first member of the new phylum Cycliophora, a group of microscopic aquatic animals living attached to lobsters’ body which contains only two species, was also found on a scampi!
Despite their name, Squat lobsters belong to the same group as hermit crabs, even if they do not carry a shell on their back like their relatives. The majority of Squat lobsters spend their time on the sea floor, hidden in crevices or under rocks to protect their body. These animals are quite small, growing from a few millimetres to 9 centimetres, but have long claws which can reach more than six times the body length! Some species use their claws to scoop up and sift sand to find food. Other species can feed on wood such as timber from shipwrecks!
Living in the perpetual darkness of the sea from hundreds to thousands of meters deep, Blind lobsters are eyeless like most animals which never see daylight. This pink crustacean has long and slim claws which may help him to locate and capture food.
Very colourful Reef lobsters inhabit shallow waters in rocky and coral reefs in the Indo-Pacific Ocean, Caribbean Sea and warmer parts of the Atlantic Ocean. Sometimes red, orange or purplish, they also can be adorned with stripes, spots or rings and their bright colours make them highly prized in the aquarium trade. However, an unregulated collection could endanger Reef lobsters with the majority of species is considered ‘data deficient’ by the International Union for Conservation of Nature: “no catch data for [these] species [are] available and it is unknown if the harvesting of wild specimens has any significant effects on its population size.” Scientists currently do not know the effects of harvesting on Reef lobsters and further research is essential to improve our understanding of species’ ecology and to put in place appropriate conservation measures.
The Department of fisheries of Western Australia edited a fact sheet about the differences between the four most common species of freshwater crayfish that occur in WA and gives the basic keys to identify them.
If you want to learn more about rock lobsters from Western Australia, consult the fact sheet edited by the Department of fisheries of Western Australia dedicated to the Western Rock Lobster.
The Department of fisheries also wrote a fact sheet about the Marron, a freshwater crayfish endemic of Australia and which is also the third largest species of freshwater crayfish in the world.