9.1: Invertebrate Diversity

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How are these jellyfish like an insect?

Jellyfish and insects don't seem to have much in common. They look much different. They live in very different environments. But both of these animals are classified as invertebrates.

What Are Invertebrates?

Animals are often identified as being either invertebrates or vertebrates. These are terms based on the skeletons of the animals. Vertebrates have a backbone made of bone or cartilage (Cartilage is a flexible supportive tissue; you have cartilage in your ear lobes.). Invertebrates, on the other hand, have no backbone (Figure below). Invertebrates live just about anywhere. There are so many invertebrates on this planet that it is impossible to count them all. There are probably billions of billions of invertebrates. They come in many shapes and sizes, live practically anywhere and provide many services that are vital for the survival of other organisms, including us. They have been observed in the upper reaches of the atmosphere, in the driest of the deserts, and in the canopies of the wettest rainforests. They can even be found in the frozen Antarctic or on the deepest parts of the ocean floor.

Snails are an example of invertebrates, animals without a backbone.

All vertebrate organisms are in the phylum Chordata. Invertebrates, which make up about 95% (or more) of the animal kingdom, are divided into over 30 different phyla, some of which are listed below (Table below). Numerous invertebrate phyla have just a few species; some have only one described species, yet these are classified into separate phyla because of their unique characteristics. For example, sponges, with pores throughout their body, are from the phylum Porifera. Crabs and lobsters, with jointed appendages, are from the phylum Arthropoda.

Phylum	Meaning	Examples
Porifera	pore bearer	sponges
Cnidaria	stinging nettle	jellyfish, corals
Platyhelminthes	flat worms	flatworms, tapeworms
Nematoda	thread-like	Nematodes, heartworm
Mollusca	soft	snails, clams
Annelida	little ring	earthworms, leeches
Arthropoda	jointed foot	insects, crabs
Echinodermata	spiny skin	Ssea stars, sea urchins