Invertebrate

2007 Schools Wikipedia Selection. Related subjects: Organisms

Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. The group includes 97% of all animal species—all animals except vertebrates (fish, reptiles, amphibians, birds and mammals).

Lamarck followed Linnaeus' division of these animals into two groups, the Insecta and the Vermes, but they are now classified into over 30 phyla, from simple organisms such as sponges and flatworms to complex animals such as arthropods and molluscs.

Since invertebrates include all animals except a certain group, invertebrates form a paraphyletic group. (For a full list of animals considered to be invertebrates, see animal.) All the listed phyla are invertebrates along with two of the three subphyla in Phylum Chordata: Urochordata and Cephalochordata. These two, plus all the other known invertebrates, have only one cluster of Hox genes, while the vertebrates have duplicated their original cluster more than once.

Phyla and common examples

• Porifera — sponges
• Cnidarians — jellyfish
• Platyhelminthes — flatworms
• Nematoda — roundworms
• Annelida — earthworms
• Echinodermata — sea star, sea urchins, sea cucumbers
• Mollusca — squid, snails
• Arthropoda — insects, ticks, spiders, grasshoppers, lobsters, crabs
• Bryozoa — moss animals, sea mats (occasionally resemble corals)