IN TOUCH WITH NATURE

Otago Witness, Issue 3853, 17 January 1928, Page 10

IN TOUCH WITH NATURE

THE WATER FLEAS

By

J. Drummond, F.L.S., F.Z.S.

Mr E. W. Bennett’s microscope at Canterbury Museum has thrown interesting light on the methods of some strange creatures of the waters. They are known popularly as water fleas, a title to which they have no claim. Men of science have given them a much better and much apter title—copepoda, meaning feet used as oars; and it is this titular character that has attracted Mr Bennett’s studies. Each leg in each pair of legs belonging to a copepod is joined by a flattened plate. When one leg is moved the opposite one moves. When all move simultaneously with the precision of men in am eight-oar the copepod moves through the water. Mr Bennett’s observations are associated with a fresh water copepod, plentiful in stagnant pools in at least some parts of New Zealand. It is obligingly docile under the rniscroscope, where it shows off its skill and prowess with its wonderfully fashioned feet.

Its legs usually are held straight forward in a bunched position. A simultaneous backward bending of the legs, with a counter-bending of the abdomen, drives the copepod forward for a short distance. The padding is not continuous, but is a repetition of strokes, causing progress by a series of jerks. The legs often are kicked backwards. This does not drive the copepod forward appreciably, but seems to free the legs or the body from entangled particles of rubbish. But in the copenod’s swift, sudden flight through the water, so sudden, seen under a rniscroscope, that little more than circumstantial evidence is available to explain the mechanism that produces it, the propulsion seems to be provided by a pair of feelers in front of the head. Each stroke they give drives the copepod straight forward. From their large muscles come the necessary powerful stroke. Their great length gives them a leverage much greater than the leverage of any other appendages. Bristles at their tips grip the water like the blade of an oar in a way that causes the water at the extreme tips to act as a fulcrum. Finally the normal position of the feelers springing almost straight out from the head, is favourable for a sudden dart at short notice, without preliminary adjust-' ment. After a sprint they 7 resume their outstretched position so rapidly that the copepod’s movement is slightly checked by the friction.

Other feelers further back are long and muscular and well equipped with hairs and bristles. Their strength and leverage are sufficient to drive the copepod forwards slowly. As these feelers move with great rapidity, the forward movement they cause is continuous. It is strangely persistent. The copepod may be buffeted with a delicate brush, or it may be almost completely deprived of water, but the rowing continues. In shallow water, several individual copepods may meet and row up against one another. They do not usually change their course, and soon there may be seen the strange sight of copepods rowing for till their worth, hut making no progress, or progressing slowly in the direction selected by the majority.

Many copepods are so beautiful that matter-of-fact men of science whose minds are occupied mainly with the creatures’ structure pause to marvel at their gorgeous colour schemes, produced by pigments in the skin, which has taken on most brilliant colours. Sir Arthur Shipley found them as beautiful as birds of paradise. He has compared them to a display of fireworks. In the mysterious Sargasso Sea Mr W. Beebe, New York, found copepods he compared to snow crystals. . There he saw bizarre forms with amazing appendages. On the vessel in the dark a small dish of copepods glowed like a tray full of diamonds, but in the light no trace of luminescence could be discovered. Yet now and then, through the microscope, there came a flash as of fire-opal. This was narrowed down by the lenses little by little until in the field of vision there was a single oval copepod, an eighth of an inch long. Seen from its side, it was merely a tissuey line. When it was turned on its back every colour of the spectrum was kindled.

This glory is concealed from the unaided human eye. As it can be seen only through a microscope, it is lost to all except a few. Mr Bennett’s copepod—its name, Boeckella triarticulata, certainly is not a pretty one—sometimes is almost pure white, relieved by the red of the single eye at the front of the head. When the colour scheme i more elaborate the dominant colour is reddish-brown, but the female’s body may be diffused with blue. A fair number of females have an intense inky blue on the upper parts of the segments of the body and at the bases of the legs, with more diffused shades of blue in other parts. The blending of blue, brown, and white is described by Mr Bennett as very beautiful. At night the cyclopean eye is a conspicuously glistening red spot. The creature is strongly attracted by light, but is excited and repelled if the light is too intense.

There are fresh water copepods, and copepods that live in the ocean. Their numbers in the ocean are enormous, their realm is as boundless as the Seven -Seas themselves. No other creatures of the sea are so versatile in using the food reserves of othr animals. Some live in an apparatus used by sea-squirts for collecting food, and steal from the stores; some live in the digestive canals of feather-stars; some live on the gums of

crocodiles. In turn, copepods are sources of food for fishes. Although only about, perhaps, one-sixteenth of an inch long, they, indirectly, help to nourish the big* gest and bulkiest creatures in the world* xu i shales, which feed on sea-animals that feed on copepods.

The Hon. G. M. Thomson, Dunedin, has seen copepods only one-fiftieth of an inch i?x n x?’ , He ,. has seen species whose delicate little bodies are adorned with bands on splashes of red, blue, or yellow. During trawling in Tasman Bay, Nelson, the water in bottles into which the tow-net was washed, was turned almost pink by the countless numbers of a tiny copepod with bright red markings on its body, Mr Thomson states that many species, aq if not sufficiently beautified by colours, are highly luminous, shining with a phosj phorescent light. He describes darting about very swiftly in jerky move? ments, caused by the rapid and simul? taneous sweep of all their fringed feet. Individually, they are insignificant. CoL lectively, being the main food of larger creatures, they are one of the most im? portant forms of the infinite variety of life in the ocean. _,J n )’ iew an account in July last by Miss Stevens, of Inglewood, Taranaki, of tame eels which fed from her hand, there is much to interest readers of this column in “ The Aquarium Book,” by Mr E G Boulenger, director of the London Zoo. logical Society’s Aquarium. His experi. ence is that, the way to a fish’s heart iq through its stomach. In his aquarium, carp take bread, biscuits, and nuts from the hands of an absolute stranger. The appearance of a keeper with a dish of food causes, in most of the tanks, a joyful riot. A conger eel, 6ft long, after it has once been fed, never objects to being lifted out of the water. Cod, small skate gurnard, and many other fish nestle on the. open palm. Crayfish clamber from their tanks in a body at the sight of food, and take their daily ration from the keeper’s fingers. Feeding time at the Brighton xAquarium is announced by the blast of a whistle, which, ip many fish, causes almost a state of hysteria. A porpoise was intelligent and inquisitive. Only two weeks after capture it took food from the hand. It consumed 301 b of fish a day.. During its few months of captivity it made a non-stop swim, covering more than 180 miles every 24 hours Mr Boulenger assures the public that people who become interested in an aquarium never tire of their hobby, the wonders I V • e , , water amply repaying them for their labour, time, and trouble. This is readily believed by readers of his beautifully illustrated book, in which he sketches the life histories of his pets and tells many stories about them. In a , c °rner of Mr A. Marshall’s garden Dillons Point road, Blenheim, last year there was a song thrush’s nest in a small clump of bamboos. The site was very unsuitable, as the bamboos were violently swayed by every high wind. Several otb ?r nests belonging to a song thrush, a goldfinch, and a hedge sparrow, were built in the hedges. This year Mr Marshall found a nest in an ornamental plum tree, about a yard from the bamboos, in which three young song thrushes appeared, but whether it was last year’s bird that built or not he cannot say. The young ones were there about November 23. but on looking into the nest on December 2, it being quite low- down, he was surprised to see the adult bird, now sitting on five eggs. Except in the case of sparrows, he never before had seen a nest used twice in succession. This nest is somewhat shallow, and is not built with much care.