NATURE NOTES

Evening Post, Volume CXIII, Issue 30, 5 February 1927, Page 15

NATURE NOTES

STORM SHELLS

THEIR UNSINKABLE RAFTS

(By E. H. D. Stidolph, 8.A.0.U.)

Among a collection of marine shells sent to the writer from Manakau, on tho Mauawatu coast, are some choice specimens of one of the most beautiful of New Zealand's marine shells. They are commonly called storm shells. Three species are known in New Zealand waters, and all inhabit the open sea, and consequently can onljf be procured when washed ashore'on an ocean beachl "A curious feature connected with them," writes Dr. C. E. K. Bucknell in his "Sea Shells of New Zealand," "is that they construct an unainkaWe raft of clear, colourless, gelatinous material enclosing air bubbles. This raft, which is made by both sexes, i 3 utilised by the female to carry her eggs. It can be detached when no longer required, but the animals are often caught unawares, and the raft is then the means-of their undoing, for they are driven ashore in great numbers when gales are blowing. . .One day, during a pronounced storm, I picked up about forty Janthina balteata, alive, and each one equipped with a raft; arid, on arriving home, placed them in a bowl of water. ; They certainly floated, but, contrary to my expectations, they floated with the mouth directly upwards, and consequently the base and the spire were both equally exposed to the sunlight; so that we may safely assume, that there are factors other than sunlight concerned in the formation of colour. ■ The specimens in question were found in company with numbers of small jellyfish, a species of Valella, beautiful little creatures of glassy appearance, with a narrow margin of ultramarine blue on the triangular sail, which is erected upon a somewhat thickened and oval disc of the same colouring. The violet snails feed, upon these jellyfish, and probably upon small Physalias, commonly known as Portuguese Men-of-War, which were also present in, great quantities.. It was interesting to observe how the colour of these two fish was invariably of an intense ultramarine or deep indigo blue, and the bluish purple of the Janthinae, with their glossy gelatinous floats, made it no easy matter.to distinguish the shellfish from the jellyfish." One species has the upper portion of the spire much paler than the violet coloured base, another has a shell _of pure pinkish violet, and tho remaining species is a true violet colour, polished.

Molluscs form one of the principal divisions of the animal kingdom, containing nearly 60,000 different species. The limpet, the snail, the slug, the oyster, and the octopus are familiar examples of this group of animals. Members of this division are very successful from the point of view of adaptability. They have, populated the sea at nearly all depths; they have populated the fresh water and the land. The land' forms. are to- be found in forests, deserts, cultivated soil; and on high mountainous and rocky localities. In outward. appearance they show great variety. The shell, which is one of the chief distinguishing features, is one of the most attractive of natural objects. Among the shell-less forms are to be found some of the most beautiful of living animals. The molliisca, which are soft-bodied invertebrate animal*?, are divided into five main classes, which differ radically in tHtk structure, details, and mode of life. Some of the molluscs are active, strong, predatory creatures, the foot divided into a circlet of strong sucker-bearing arms. These