WAYS OF THE WILD.

Auckland Star, Volume LXVII, Issue 151, 27 June 1936, Page 1 (Supplement)

WAYS OF THE WILD.

STAR FISH AND SEA URCHINS

WELL KNOWN ON SEASHORE.

(B v A. T. PYCROFT.)

The star fish, the sea urchin, the brittle star and the sea cucumber are well known to all frequenters of the seashore. They, with other relatives, are placed in one great group of animals, the subkingdom ecliinodermata, meaning "spinyskin." In some types the spiny nature of the body is perfectly obvious, as in the sea eggs, or kina, of the Maori. The rough surface of these various animals is due to the presence of a crystalline deposit of carbonate of lime. In a sea urchin, or a brittle star, this depotsit is in the form of little plates, which build up a more or less rigid surface, whereas in the star fish it usually forms a kind of scaffolding between which there stretches the more yielding, leathery skin. In the ordinary sea cucumber the deposit consists only of small spicules or points. It is this same deposit that forms the spines of a sea urchin and has given the name of the group "spinyskin," from two Greek words ecliinos, a hedgehog, and derm?., skin. The tendency of these animate —echinoderms —to deposit lime is not confined to the skin, the walls of the internal organs being often strengthened by similar material. Universal Distribution. In geological history the ecliinodermata as a whole have been traced as far back as old palaezoic formations, and some classes have persisted throughout the succeeding ages to modern times. Today one finds members of the group living on the sea and estuarine shores between tide marks and in varying depths down to the dark and abysmal depths of the ocean. The distribution of these animals is universal. Some forms dwell in the waters of the icebound polar regions, some in the milder waters of the temperate zone, while others again welcome a home in the warmer waters of the tropios. A number of inter-tidal forms are extremely hardy, and, living in exposed places, seem to find no discomfort when buffeted by the waves, or exposed between tides to the rays of the sun; others migrate from shallow to deep water and vice versa, according to seasons, while others, being extremely delicate and fragile, seek either the permanent shelter of deep water or some secluded recess in a rock pool or corallocked lagoon. Usually the various types adhere to their chosen habitat, and may be sharply defined from their immediate relatives according to location. Geographical distribution also is concerned in determining the habitat of certain species. Generally speaking, a distinct fauna exists in the three main belts of latitude, the frigid zone, temperate zono and torrid zone, and the distinction is so apparent in most cases that a specialist has no difficulty in determining the zone whence a given specimen comes. The sea stars are readily recognised by their resemblance to a star in shape. Usually they are five armed, but in some

families the number of arms may be anything from five to twenty-five in number, excepting, of course, abnormalities and aberrant forms. The colours in life vary considerably both in. species and individuals. In one spec'es the body is a uniform 1 bright blue, in an allied form a bright biscuit, yellow or orange, and in another dark green or a drab brown. Some species have a colour pattern which may vary in vivid colours like crimson, bright orange, mauve, pink and various shades of blue. Star fish are sluggish animals, rarely moving of themselves, and staying for days in the same position. When disturbed, however, a star fish can travel at a considerable pace. The dimensions of adult star fish range from about Jin to 20in across the arms; the vast majority, however, are only of moderate size, and rarely exceed lOin across. Their muscular system is poorly developed, and this and the more or less rigid skeleton permit of only a 6low and limited range of actual body movement. The mouth occupies a central position on the under surface of the body. It is surrounded by special plates armed with spines, which no doubt serve to protect the soft tissues within the mouth aperture. The stomach is produced laterally into pouches, which, in five-rayed examples, arrange themselves into five pairs. A pair projects some distance down each arm, and in this manner the area of absorption is considerably increased. The diet of sea stars consists of small animals and fragments of animal matter. The power to grow fresh limbs, which are more or less perfect reproductions of parts dismembered either accidentally or as a result of self-mutilation, is vested in the sea star as well as in other types of animals. Sea Urchins. The sea urchins are the best known, as they are the most numerous of all members of the sub kingdom echinodermata. The plates of the shell of the sea urchin are, like the sea star, covered with rounded tubercles, or lumps, of various sizes, and in the sea urchins it is to these that the spines are attached \ by a ball and socket joint, surrounded Iby muscles that can move the spines in any direction. Sea urchins, like star fish, have tube feet, which arc all provided with suckers at tne end which the animal stretches out and attaches to smooth, surrounding objects, and it is thereby able either to hold itself firm against waves or currents or to pull itself along. The mouth is on the under part of the sea urchin, and the vent at the summit. The mouth contains five pointed teeth. They arc part of a very elaborate masticating apparatus. This consists of 20 principal pieces arranged into a five-sided conical mass, compared by Aristotle to a lantern. In the centre of the whole are the five teeth working in body sockets, or pyramids, connected by muscles with one anothov with the interior of the shell and wHli arched processes that surround the mouth opening. Some sea urchins possess eyes. These creatures arc bot!« animal and vegetable feeders, and are even c when oppor' jnity offers.