CRABS THAT BEAR ARMS

Hokitika Guardian, 11 April 1931, Page 2

CRABS THAT BEAR ARMS

SCI ENTIST’S DISCOVERY. (By Thomas R. Henry). Crabs that wear clothes, others that carry arms, and still others that march in vast numbers like soldiers are among tlie curiosities of crustacean life brought to tlie National .Museum Washington, by Dr Aleibouriio YY’anl, F.Z.S., Australian zoologist, who found them on the Great Barrier coral reef off the Australian coast. Among tlie most curious is a Huy crustacean which forces the coral polyp to build a limestone palace for its abode. The female of this species. Dr Ward explains, lodges on the corn I when in a larval state and causes an irritation which leads tin l host animal to build up the limestone walls. The resulting house is just large enough for the crab to move, about in comfortably. There is always a door through which she obtains food. Another smeeies merely sits on the end of a coral sprout which, growing outward, makes a long, circular burrow for tlm animal. Through this it can move hack and forth at will. The forward part of its body is enclosed in a hard shell of the exact colour of the coral, so that when it sits at the :loor of its burrow to obtain food it is impossible to distinguish it. It completely closes the entrance to the burrow, But the most curious of all is the crab which carries two sea anemone, ore in each hand, wherever it goes. Tn its first few months of life it seizes these anemone—also living animals with stalks and discs like flowers and which originallv are attached to rn'-ks under the water—about the middVs of their stalk's, and thenceforth sal'i s forth like a person carrying two umbrellas. The most logical explanation of this behaviour. Dr AVard says, is that tin anemone serve as weapons, killing or paralysing small sea animals which conic in contact with them. These then serve tlie crab ns food. !he species of anemone carried lias stinging cells in its disc. These curious weapons are carried by the crab continuously and seem essential to its life. AATien one of them is taken away the animal moves automatical!” to grab it again. AA lien ‘a 1 crab is killed slowly in alcohol it clings to its weapons even in its death struggles. TAILOR CRABS. Then there are the spider crabs which cut and wear clothes. They have tin v hairs protruding through their s’holls. Thev cut sections of living sponges and place them on their hacks. The sponge becomes entangled in the hairs and continues to grow so that it protrudes for several inches over the hack. Thin layers also cover the under parts of the body and the l c £ s - A closely related species cuts sections of sponges and carries them . with its hind legs so that they cover its body. Every time tho crab sheds its shell it must make itself a new suit. This practice, Dr AVard explains, probably is beneficial to both animals. The crab, living in a forest of sponges, looks like a sponge itself and thus is protected from its enemies. The sponge benefits by being carried to new loud sources. AY hen the shell is shed, the sponge simply attaches itself to a rock and continues growing... One of the most remarkable cases of commensalism yet found in nature was described by Dr Ward in thd case of a degenerate type of barnacle which makes its way through the thin shell of one of the Barrier Reef crabs where a hair comes through. It wanders through the blood stream of the crab and finally conies to the .surface, forming a little sac for itself. Here it is metamorphosed into another form and sends long, thread-like shoots into every part of the crab’s body except the vital organs which it encircles without penetrating. Tn some respects it is like a cancer among higher animals, except that in this case the “cancer” is an individual animal of another species. Thus i T lives off the food P aten by tlie crab, but never kills its host.