Science Fair Project Encyclopedia
Protostome
Protostomes (from the Greek: first the mouth) are a major group of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development. In protostomes development, the mouth forms at the site of the blastopore, and the anus forms as a second opening.
Current molecular data suggest that protostome animals can be divided into three major groups:
- Ecdysozoa, e.g. arthropods and roundworms
- Lophotrochozoa, e.g. mollusks and annelids
- Platyzoa, e.g. flatworms
Of these, the latter two make up the Spiralia, including most animals where the embryo undergoes spiral cleavage.
10-26-2009 08:16:03
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details