Some of these animals can be identified with the great groups described by zoology,such as the wiwaxia with the mollusks and the peytoia shaped like a slice of pine apple, forerunner of the coelenterate. Others were unknown and, to our eyes today, utterly absurd the Hallucia, with lots of little mouths and 12 still-like legs and the Opabina, with a large month on the end of a long tertacle 2
Two parts of evolution
But what was going on in those waters so long ago has a lot to do with us today. Animal-life was evolving along two differant paths. On one other were the chordates, rope-like creature s that evolved into the vertebrates and fish, the subject of this volume, are vertebrates. It is curious to note that the force of evolution, the ability to create new paths. Apart from a number of curiously shaped creatures, all inevitably destined to disappear from the face of the Earth, the invertebrates spread rapidly, developing forms that were very refined as movers, hunters and defenders, while the chordates took a long time to make their mark. They may already have existed in the seas of the Cambrain Period, in the shape of little swimming animals like the pikaia, but they were a minority compared to the invertebraates. There are only a few living representatives of these ancient fish forerunner left , and they probably come from the sterile branches of the chordates. They include the urochords, or tunicates; like the ascidians,the actual cord, called the notocord, is only in the tail and only in the larval stage, because the adilt, with its barrel-shaped mouth, has nothing whatever to do with the general organization of the chordated.
Some of these animals can be identified with the great groups described by zoology,such as the wiwaxia with the mollusks and the peytoia shaped like a slice of pine apple, forerunner of the coelenterate. Others were unknown and, to our eyes today, utterly absurd the Hallucia, with lots of little mouths and 12 still-like legs and the Opabina, with a large month on the end of a long tertacle 2Two parts of evolutionBut what was going on in those waters so long ago has a lot to do with us today. Animal-life was evolving along two differant paths. On one other were the chordates, rope-like creature s that evolved into the vertebrates and fish, the subject of this volume, are vertebrates. It is curious to note that the force of evolution, the ability to create new paths. Apart from a number of curiously shaped creatures, all inevitably destined to disappear from the face of the Earth, the invertebrates spread rapidly, developing forms that were very refined as movers, hunters and defenders, while the chordates took a long time to make their mark. They may already have existed in the seas of the Cambrain Period, in the shape of little swimming animals like the pikaia, but they were a minority compared to the invertebraates. There are only a few living representatives of these ancient fish forerunner left , and they probably come from the sterile branches of the chordates. They include the urochords, or tunicates; like the ascidians,the actual cord, called the notocord, is only in the tail and only in the larval stage, because the adilt, with its barrel-shaped mouth, has nothing whatever to do with the general organization of the chordated.
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