Taxonomy
Characteristics
Turbellaria are generally small (<1 - 60cm) and free-swimming. Their locomotion depends on cilia. Most turbellaria are carnivorous, and actively scavenge for food. Most species are marine and freshwater dwellers, but some have evolved to dwell on humid land, as well.
Planarian (Dugesia)
The planarian Dugesia is a common representative of Class Turbellaria. This common flatworm can be found in freshwater habitats. Their digestion tract consists of a central tubular pharynx, which is extended out of the body cavity for feeding. Digestive enzymes are excreted from the pharynx, and thus digestion begins outside of the body. Muscular pumping motions bring the liquefied food into a 3-branched intestine. Each branch consists of ceca, which delivers the nutrients to the body. This worm is blind-ended, meaning there's only one way in and one way out; it consumes food where the feces exits (Gilbertson, 1999).
Planarians have ocelli (eye spots) that detect the amount of light in the nearby environment, and auricles (ear-like flaps) that detect the amount of water current.
References
- Gilbertson, Lance; Zoology Lab Manuel; McGraw Hill Companies, New York; ISBN 0-07- 237716-X(fourth edition, 1999)
