‘Fluffy’ crab that wears a sponge as a hat discovered in Western Australia
A“fluffy” crab discovered off the coast of Western Australia has been named after the ship that carried Charles Darwin around the world. The new species, Lamarckdromia beagle,belongs to the Dromiidae family, commonly known as sponge crabs.
Crustaceans in this family fashion and use sea sponges and ascidians – animals including sea squirts – for protection. They trim the creatures using their claws and wear them like hats.
Dr Andrew Hosie, a curator of crustacea and worms at the Western Australian Museum, said sponge crabs had hind legs that were specially adapted for holding their protective hats.
“The sponge or ascidian just keeps growing and will mould to the shape of the crab’s back,” he said. “It will never attach … it forms a nice cap that fits quite snugly to the top of the crab.”
Similar to how hermit crabs use shells for protection, the sponges help Dromiidae crabs to camouflage from predators such as octopuses and other crabs.
The sponges can be bigger than the crab itself, and also provide a chemical deterrent. “Some of the compounds that these sponges are producing are very noxious,” Hosie said. “There’s not a lot of active predators that would be interested in munching through a sponge just to get to a crab.”
A family living in Denmark, Western Australia found a Lamarckdromia beaglespecimen washed up on the beach and sent it to the Western Australian Museum for identification.
Hosie and Colin McLay, a marine biologist associated with Canterbury University in New Zealand, then described the crab as a new species – one of three sponge crabs in the Lamarckdromiagenus.
Comparing the new crab to others in the museum’s collection, they discovered several Lamarckdromia beaglespecimens that were previously unidentified or misidentified. The earliest L beaglespecimen they found dates from December 1925.
Hosie said it wasn’t clear why Lamarckdromia beagle was so fluffy. “The sponge or the ascidian that these things carry should offer it all the camouflage it needs,” he said. “I expect that having the extra fluffy legs means that the outline is even more obscured.”
“The hair doesn’t help with holding the sponge down. It’s not like it’s Velcro, unlike some … spider crabs that will put seaweed on their back – their hair is hooked and stiff like Velcro.”
The crab’s name commemorates the HMS Beagle, whose second voyage between 1831 and 1836 led to Charles Darwin’s theory of natural selection. The ship carried Darwin to King George Sound – the site of Albany on Western
Australia’s south coast – in 1836.
“Also because it’s tanned, it’s kind of like a beagle colouration,” Hosie said.
Lamarckdromia beagle was described with other new species in a paper published in the journal Zootaxa, which detailed 31 species of sponge crab known to be found in Western Australian waters.
“Discovering new species in Western Australia is not an unusual thing,” Hosie said. “The amount of things we don’t know we’ve got in Australian waters is still very high.”