“From out thy slime
The Monsters of the Deep are made.”—Byron.
AMONG the multitudinous hosts of living creatures which throng the Ocean, vast hordes are furnished with some kind of protective armour, the better to take their part in the ceaseless warfare for existence.
Though the armour differs widely in different kinds of animals, they offer one and all a great contrast to the soft jelly-like Medusæ.
Starfishes and Sea-urchins, for example, are guarded by tough or hard skins, with actual plated armour and sharp prickles. Limpets are sheltered behind single firm shields, and in any moment of peril become instantly glued by suction to a rock. Oysters dwell within stout bivalve shells. Hermit-crabs carry with them empty purloined shells, of other creatures’ construction. Crabs and Lobsters wear strong suits of sheltering armour, joined together bit by bit, as knights and squires of old were clothed from head to foot in the many “pieces” of a mediæval soldier’s military suit.
The armoured hosts belong to various divisions in the Animal Kingdom,—starfishes and sea-urchins to one; limpets and oysters to another; crabs and lobsters to a third. And all three, together with microscopic jelly-specks and sponges and coral-polyps and medusæ, belong to a much greater Division, which embraces all “Invertebrate” or Backboneless creatures.
If they have not backbones and ribs, they have skeletons of a kind. Only, as a general rule, the skeletons lie outside or are visible through the transparent body, instead of being hidden away inside, as in most fishes.
The prickly-skinned starfishes and sea-urchins are familiar objects with most of us.
Both belong to a Division in the Animal Kingdom which is well above the level of jelly-fishes. Both have arms or rays, proceeding from a central disc. But in the starfish the rays are separated; in the sea-urchin they are joined together.
Starfishes and sea-urchins are able to move and even to travel, though in most cases with extreme deliberation. Both can put out little tube-feet suckers, by means of which they can change their position, and can even slowly right themselves, when turned the wrong way up.