Category: Invertebrates
Hydras make up a genus of tiny (up to 10 mm long), tentacle, aquatic, predatory animals that are commonly found in unpolluted ponds, lakes, and streams in temperate and tropical regions. They are of special interest to science because they do not seem to age or die of old age. While generally stationary, or sessile, they are able to move themselves when necessary by bending over and grabbing onto the substrate with their mouth and tentacles while releasing with their “foot” – using this motion, they are able “loop” or “somersault” several inches in a day!
The world’s first Animals
Invertebrates were the first animals to evolve. While their soft bodies left precious few records behind, there are fossils of sponge-like animals that are 665 million years old, as well as traces of tracks and burros from worm-like animals going back 1 billion years. By comparison, the earliest birds appeared only 150 million years ago! And not only were invertebrates first, they are the most plentiful of animals - it is estimated that 97% of all animals living on the Earth today are invertebrates, with several groups containing more species than all vertebrates combined!
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