THE SEA ANEMONES.
Besides the Polypi just mentioned as nearly related to the fresh-water Hydra and those forming the different kinds of Corals, the sea produces a vast number of other Zoophytes, the commonest kinds of which are well known as Sea Anemones. These animals are found adhering to rocks on all shores; they consist of a rather thick column, the base of which forms an adhesive disc, while its summit, which is also a disc, shows a puckered mouth in the centre surrounded by several rows of tentacles. The tentacles are sometimes short and stout, sometimes long and slender; they are generally adorned with vivid or delicate colours, often disposed in rings and contrasting beautifully with the colours of the stem and disc. In their expanded state they present a close resemblance to a flower, and indeed vie with many flowers in beauty; hence the name of Animal Flowers was given to them formerly, and has now given place to that of Sea Anemones, although they are rather to be compared with those composite flowers in which numerous petal-like flowerets radiate from a central disc. When contracted, the Sea Anemones resemble soft knobs or buttons, with a depression at the top.
In describing the Stony Corals, the fact has been mentioned that the Polyps, which may be regarded as the architects of those extraordinary structures, are very similar to the Sea Anemones. In the latter, the cavity surrounding the central stomach is partially divided into chambers, by partitions, which run inwards from the circumference towards the centre; in the Coral Polyps each of these partitions produces a stony plate in its substance, and these plates form the rays which occupy the interior of the Polyp-cell.
The Sea Anemones move slowly along by the action of their adhering disc, somewhat in the same way that a snail or slug crawls upon the ground. Their food is obtained by means of the tentacles which give them their beautiful flower-like character, and to render them efficient organs for this purpose they are endowed with a singular provision. The skin of the tentacles, and, indeed, of most parts of the Sea Anemone is filled with little cells or vesicles, each containing a spiral thread, which when touched instantly darts forth, and penetrates the body coming in contact with it. In this way, if a worm, a small fish, or any other soft animal touches the tentacles of an Anemone, it is instantly transfixed with innumerable delicate darts, which not only assist the tentacles in holding the destined prey, but also seem to exercise a sort of numbing influence upon the victim, deadening his struggles and rendering him an easy conquest. He is then speedily passed by the tentacles to the orifice of the mouth, and swallowed without mercy.
One of the commonest kinds of these Polyps is the Mesembryanthemum (Actinia Mesembryanthemum), a large, usually liver-coloured species, with a row of blue warts round the margin just outside the tentacles. It is found abundantly on the rocks of our Southern coast especially. The Thick-horned Anemone (Actinia or Brusodes crassicornis) is another large and fine species, usually of a red colour, with very thick tentacles, which are generally white with pinkish bands.—The Sea Cereus (Anthea Cereus) has long slender tentacles, which are not retracted in the same way as those of the Sea Anemones generally. The tentacles are usually tipped with a pink or purple tint; they are constantly waving about in the water in search of prey; and instantly seize upon any creature that passes over them.—The Parasitic Anemone (Actinia parasitica) and the Cloak Anemone (Adamsia palliata) always attach themselves to univalve shells which are occupied by Hermit Crabs.