Insects and crustaceans are closely related to soft-bodied marine worms.
Segmented worms and arthropods (insects, crustaceans, and their relatives) both evolved from a soft-bodied, segmented ancestor.
Segmentation is a simple way to become larger, because each segement is a duplicate of the next. By coordinating the muscle action of independent segments, the animal can move forward.
Annelids (AN-nel-ids): animals with soft, segmented bodies, including earthworms and extinct, marine Canadia
New feature
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body segmentation increases size and facilitates locomotion and burrowing
Aysheaia (a-she-A-ah): an extinct, segmented marine animal that is thought to be related to the living Peripatus
New features
- flexible external skeleton helps protect the animal from changes in the environment and provides body support
- lateral appendages for walking, climbing and catching or manipulating food
Arthropods (ARTH-ro-pods): segmented animals with jointed "legs", including trilobites, insects, and crustaceans
New feature
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jointed "legs" for walking, feeding, breathing, and sensing (touch, taste, etc.); muscles in both body and "legs" control movement
PICTURE CAPTIONS:
- annelid
Canadia (kan-ah-DEE-ah) - arthropod relative
Aysheaia (a-she-A-ah) - arthropod
trilobite (TRY-lo-bite) - Diagram showing common ancestry and evolution of annelids, Aysheaia, and arthropods from organisms with a segmented body. Evolution of Aysheaia and arthropods is where flexible external skeletons and paired lateral appendages branch off.