If we take a common starfish and turn it upon its back, we observe that the lower portion is covered with short tentacles, each having a little sucker on the end. These are the feet of the starfish, by which it walks or moves. In the center of the body is the mouth leading into the stomach which reaches into each ray. The eyes are at the tip of each ray. On the back of the star we find a little red disk with a rough surface. This is really a sieve for straining the water which pours in through a little canal encircling the mouth and leading off into each arm, carrying water to each one of the myriads of feet.
The feet move independently, and the starfish walks much faster than would be imagined. This can be illustrated by the sudden appearance of the starfish, in Long Island Sound. One night when the oyster men left the beds no starfishes were seen. The following day they were there in such vast quantities that it was estimated they covered the entire bed, two or three deep, and tens of thousands of dollars were lost by the destruction of the oysters.
How an oyster can be opened by a soft, helpless starfish would seem a mystery; but it is a very easy matter. The starfish drags itself over the shell and places its mouth at the end, extending its long arms downward, literally swallowing part of the shell. It is supposed to eject some secretion into the shell that causes it to open.
VIII. OCEAN HEDGEHOGS
(The Echini)
Fig. 51.—Sea urchins burrowing in the rocks.
On the Florida Reef and off the rocky shores of California one of the most conspicuous among the rock-living animals is the black, long-spined Echinus. In the water it looks like a huge pincushion (Fig. 51) filled with black pins, points outward, and every crack and crevice is filled with them. When found on the beach, despoiled of their spines, they resemble bleached shells, and are then known in Florida as sea eggs (Fig. 52). The long black spines are continually moving up and down, and constitute the armament of the sea urchin, and an effective one to all except very large fishes, as some rays, which have pavementlike teeth fitted particularly for such not especially dainty morsels. The spines emit a bluish secretion which is left in the wounds made by them, and is more or less poisonous. This common sea urchin is a type of hundreds found in almost all seas from very shallow water to the abysmal regions of the ocean.