Invertebrates at Risk
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include insects; crabs, lobsters and their kin; snails, clams, octopuses and their kin; starfish, sea-urchins and their kin; and worms.
The majority of animal species are invertebrates; one estimate puts the figure at 97%. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata.
Some of the so-called invertebrates, such as the Chaetognatha, Hemichordata, Tunicata and Cephalochordata are more closely related to the vertebrates than to other invertebrates. This makes the term "invertebrate" paraphyletic and hence almost meaningless for taxonomic purposes.
Invertebrates can be classified into several main categories, some of which are taxonomically obsolescent or debatable, but still used as terms of convenience.
1. Protozoa (like the worms, an arbitrary grouping of convenience)
2. Sponges (Porifera)
3. Stinging jellyfish and corals (Cnidaria)
4. Comb jellies (Ctenophora)
5. Flatworms (Platyhelminthes)
6. Round- or threadworms (Nematoda)
7. segmented worms (Annelida)
8. Insects, spiders, crabs and their kin (Arthropoda)
9. Cuttlefish, snails, mussels and their kin (Mollusca)
10. Starfish, sea-cucumbers and their kin For many centuries, invertebrates have been neglected by biologists, in favor of big vertebrates and "useful" or charismatic species.