Category: Invertebrates
While similar in some ways to earthworms, leeches differ in other distinct ways – for example, leeches do not have bristles and have a sucker at each end of their body. Most leeches live in freshwater, though there are terrestrial and saltwater exceptions. They are well known for their adaptation of blood-sucking, though not all species of leech feed this way. Of the ones that do, some species are able to store more than five times their body mass of blood in their digestive system.
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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Discover Animals is a web-based educational resource offered by the NAIA
