Barnacle “Grows In Rows And Rows”

Press, Volume CVIII, Issue 31754, 10 August 1968, Page 5

Barnacle “Grows In Rows And Rows”

} (Contributed by the Canterbury Museum) Sitting on its head, with its legs all-a-kick-ing in the sea; enclosed in a shell, yet not a shellfish, the barnacle is yet another animal enigma that escaped true recognition until the nineteenth century. Barnacles were classified as shellfish, akin to limpets, whelks and their like, until in 1830, a famous naval surgeon, J. Vaughan Thompson, discovered that the eggs of barnacles hatched into tiny creatures that looked like sixlegged, hairy, water fleas, completely different from any small shellfish. These creatures are called nauplius larvae and Thompson captured them in a special net he had invented for catching the microscopic plant and animal life of the sea. Immediately he realised that barnacles must belong, not to the shellfish group, but to a great class called Crustacea, that includes such animals as shrimps, crayfish, erabs and the real water fleas. However, nearly all the barnacles were different from other Crustacea because they secreted for themselves a hard shell-plated house, around their otherwise shrimp-like body. Inside the shell, the barnacle sits upon his head. His mouth has twisted around to lie on his chest, and because he can’t walk about and capture his food, he kicks out all his legs into the sea to feed. Feeding Habits Barnacles have rather slim and hairy legs and they are arranged so that they curl forwards with all the fine'

hairs forming a net. The barnacle pushes his net through the “roof” of his shell-house and sweeps it forwards and down and back inside the shell: gulp, gulp, gulp—about as quickly as that—and with each gulp, the hairy legs grab minute particles from the water and stuff them into his mouth.

Biologists have found that young barnacles eat faster than old ones; and that all eat faster on warmer days. They also found that those barnacles that live very high up on the seashore, and which are, consequently, only covered by the sea for a few hours at high tide, eat furiously fast for the time they are covered with water. When the tide goes out, these barnacles must close up the roof of their shell-house very tightly so that they do not dry out in the air. Seeking A Home The barnacle nauplius larva that we mentioned earlier is not sedentary like the adult, but swims about in the sea. During this time it is able to disperse and spread the barnacle species away from home. This nauplius larva changes into another form called a “cypris” and it is the cypris that eventually seeks out a suitable place to settle down and become an adult barnacle. Many cypris larvae prefer to find places where there are already other barnacles of their own kind. This is important, because while the barnacle contains both male and female sex organs, that is it is a hermaphrodite, it usually needs to cross-fertilise with another barnacle. The barnacle cypris also seeks a place where there is a good current of water that will always bring plenty of food to the sedentary adult. In particularly good places on

the shore, one sometimes finds hundreds of thousands of the small species of acorn barnacles that are particulariy common on our coasts. They form white mats on the rocks or wharf piles, as well as on the hull of ships. One species breeds all the year around, and new barnacles multiply in enormous numbers, just as A. P. Herbert has described, in these lines: "Barnacle family grows and grows Little relations arrive in rows and rows." Free Travel Many barnacles, realising the limitations of a sedentary existence attach themselves to other animals and ships and so enjoy the benefits of free travel. One big barnacle is commonly found on the humpback whale and so is able to enjoy the rich soupy southern waters in which the humpback moves. Another stalked barnacle attaches itself to the shell of the whale barnacle. Some kinds attach to turtles, fishes, sea snakes and seals. Last vear, a leopard seal came ashore at Pines Beach with a healthy group of goose barnacles aboard.

A heavy encrustation of barnacles on the hull of a ship may increase its fuel consumption by as much as 50 per cent by resisting the smooth passage of the ship through the water. This is why special anti-fouling paints have been invented to dis. courage the barnacle cypris larvae from settling.

Though they do not look very fleshy, a few big species of barnacles are eaten in some countries: Spain, Brittany and Patagonia. The Patagonian dish is a monster eight inches long and three inches in diameter, at least the proportions of a small crayfish and reputedly of most delicate flavour.—M.M.D. and J.T.D.