Hairy-handed crab facts for kids
Quick facts for kids Hemigrapsus crenulatus |
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Varunidae
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Hemigrapsus
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H. crenulatus
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| Hemigrapsus crenulatus (H. Milne-Edwards, 1837)
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The Hemigrapsus crenulatus, also known as the hairy-handed crab or papaka huruhuru, is a type of crab that lives in the ocean. It belongs to the family Varunidae. This crab is special because it is found only in New Zealand. However, a similar crab in Chile might be the same species.
These crabs live in the area between high and low tide, called the intertidal zone. They can also spend some time out of the water. They get their name "hairy-handed" from the thick patches of hair, called setae, on their claws (called chelipeds) and legs. Their color can be green or brown. Adult crabs are usually 2 to 4 centimeters (0.8 to 1.6 inches) wide across their shell. Some smaller mature crabs can be as tiny as 1 centimeter (0.4 inches) wide. These crabs can live and have babies in water with many different salt levels.
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About the Hairy-Handed Crab
For a long time, scientists wondered if the hairy-handed crabs in New Zealand and Chile were truly the same species. This question started in 1837 when Henri Milne-Edwards first identified the species. He had crabs from both places but didn't say where the one he named came from.
Over the next century, scientists compared crabs from New Zealand and Chile. They found a small difference in a ridge under the eyes, called the stridulating ridge. This made some scientists think they were different species. However, in 1918, Mary J. Rathbun was the first to compare them closely and say they were indeed the same species. Later, in 2011, more detailed studies of their bodies and DNA confirmed that the crabs from both New Zealand and Chile are the same species.
Reproduction and Life Cycle
Hairy-handed crabs usually breed from June to January or February. They tend to breed more often in winter than in summer. Female crabs are ovigerous, which means they carry their eggs under their bodies. A female crab can even breed twice in one season.
Crabs usually molt (shed their old shell to grow) before and after the breeding season. If the temperature and salt levels are just right, the eggs can hatch in about 45 days. If the water has less salt, the eggs might take longer to hatch and can be larger.
As crabs grow and become able to reproduce (this is called maturation):
- Male crabs' shells grow in a more circular shape.
- Female crabs' shells grow wider in an oval shape. This wider shape helps them hold more eggs.
The smallest mature male crabs are about 1.3 to 1.5 centimeters (0.5 to 0.6 inches) wide. The smallest mature female crabs are about 0.9 to 1.1 centimeters (0.3 to 0.4 inches) wide. Males generally grow bigger, faster, and for a longer time than females. They can even become twice as large as their initial mature size.
Appearance and Anatomy
Male and female hairy-handed crabs look quite similar. Both have a roundish shell that is a bit wider than it is long when you look at them from above. Crabs from New Zealand are usually greener, while those from Chile are browner. Both sexes often have pale spots on their shells in a similar pattern. Fully grown adult crabs are typically 2 to 4 centimeters (0.8 to 1.6 inches) wide.
If you look at the crab from underneath, you can see small bumps, called granules, on the front part of its shell. Their eye sockets are wide. They also have a few small teeth along the front edges of their shell.
Male crabs tend to have more hair (they are more pilose) at the base of their claws and along their legs. Sometimes, this thick hair can even make it a bit harder for their claws to work properly. The outside of their claws is bumpy. The lower part of the claw (the fixed finger) bends downwards into the main part of the claw (the palm). Their arm is triangular and has a row of bumps across its underside.
The stridulating ridge is a ridge located under and across both eyes. In females, this ridge has continuous bumps. In males, the bumps are more separated. Differences in these patterns were once part of the arguments about whether New Zealand and Chilean crabs were the same species.
Ecology and Behavior
You can find H. crenulatus all around mainland New Zealand and along the west coast of Chile. They are euryhaline, which means they can live in water with a wide range of salt levels. This allows them to live in places like estuaries (where rivers meet the sea), brackish waters (water that is a mix of fresh and salt), and the intertidal zone.
One interesting story from 1910-1912, told by E.F. Stead, describes what happened after a big storm. A lot of saltwater flowed into a freshwater lake. Hairy-handed crabs then moved into the area and stayed until the salt levels went back to normal. In the intertidal zone, you rarely find these crabs below the low-water mark. However, more female crabs tend to live in the lower parts of this zone.
These crabs are known as burrowing crabs. They like to hide under stones or dig into sand and mud. This is because they prefer soft ground, which helps them avoid strong sunlight, very hot temperatures, and high salt levels.
Because they are semi-terrestrial, these crabs spend time away from the water. For example, they will move up the shore with the rising tide to find food in land areas when the tide is high. Then, they will go back down the shore as the water levels drop.
