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Updated: June 16, 2025
Practically all animals having a heavy calcareous shell were grouped with the snails and oysters as mollusks. But the barnacle did not fit well with other mollusks. Its shell was entirely different. It had several pairs of legs; and no mollusk has legs. The barnacle is evidently a sessile crab or better crustacean.
Forerunners of the great ammonite family of cephalopod mollusks now appear. The antique forms of the earlier Carboniferous amphibians continue, but with many new genera and a marked increase in size. A long forward step had now been taken in the evolution of the vertebrates.
One or two others were formerly equally numerous and have since become almost extinct; so the brachiopoda, which have been almost entirely replaced by mollusks. The same may very possibly be true of others. For of the amount of extinction of larger groups we have generally but an exceedingly faint conception.
In the glass tanks curious sea fish darted through the water, grotesque sea monsters crawled over the pebbles, and transparent jelly fish floated slowly; pink and white sea anemones, like a bed of flowers, opened and closed, and diminutive sea animals, almost invisible, spread thread-like tentacles; sponges and coral grew upon the rocks, and mollusks showed by their movements that they had life.
It is thus easily broken by the waves, and white fragments of coral trees strew the ground beneath. Brilliantly colored fishes live in these coral groves, and countless mollusks, sea urchins, and other forms of marine life make here their home. With the debris from all these sources the reef is constantly built up until it rises to low-tide level.
Among these some took to feeding on the borders of clear streams, picking out such larvae and mollusks as they could reach in shallow water. When food becomes scarce they would attempt to pick them out of deeper and deeper water, and while doing this in cold weather many would become frozen and starved.
Other zoophytes swarming near the sponges consisted chiefly of a very elegant species of jellyfish; mollusks were represented by varieties of squid that, according to Professor Orbigny, are unique to the Red Sea; and reptiles by virgata turtles belonging to the genus Chelonia, which furnished our table with a dainty but wholesome dish. As for fish, they were numerous and often remarkable.
In Mollusks there is a longitudinal axis and a bilateral symmetry; but the longitudinal axis in these soft concentrated bodies is not very prominent; and though the two ends of this axis are distinct from each other, the difference is not so marked that we can say at once, for all of them, which is the anterior and which the posterior extremity.
Finally nothing remains but the fibers, either gelatinous or made of horn, that constitute your household sponge, which takes on a russet hue and is used for various tasks depending on its degree of elasticity, permeability, or resistance to saturation. These polyparies were sticking to rocks, shells of mollusks, and even the stalks of water plants.
AMPHIBIANS. The vertebrates had now followed the arthropods and the mollusks upon the land, and had evolved a higher type adapted to the new environment. Amphibians the class to which frogs and salamanders belong now appear, with lungs for breathing air and with limbs for locomotion on the land.
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