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Phylum Ctenophora & Phylum Platyhelminthes – Characteristics and Examples
Phylum Ctenophora (Gr., ktenos – comb; phora – carrying)
1. Transparent body with biradial symmetry. Triploblastic.
2. Two tentacles and eight longitudinal rows of ciliary comb-plates for locomotion are present.
3. Marine, solitary and free-swimming.
4. Nematocysts are absent but colloblasts (adhesive cells) are present. Ctenophora.
5. No polymorphism or dimorphism occurs.
Examples: Pleurobrachia (comb jelly), Cestum (Venus’s girdle), Ctenoplana, Beroe (sea mitres).
Phylum Platyhelminthes (Gr., platys – flat; helmins – worm; Flatworms)
1. Bilaterally symmetrical (i.e. the left and right halves of the body have the same design) and dorsoventrally flattened animals.
2. Body thin, soft, leaf-like, or ribbon-like.
3. They are triploblastic animals implying that their tissues differentiate from three embryonic germ layers. They are without a body cavity (acoelomate animals).
4. Digestive cavity (when present) with a single opening, the mouth (anus is absent).
5. Suckers and hooks are usually present.
6. Circulatory and respiratory systems and skeleton are absent.
7. Excretory system consists of blind tubules called protonephridia. The blind end of a tubule bears a tuft of cilia or a flagellum and is called a flame bulb or flame cell.
8. Hermaphrodite, i.e., both male and female reproductive organs occur in the same individual.
9. The turbellarians are free-living, aquatic, both marine and freshwater and a few are terrestrial. Trematodes and cestodes are parasitic.
Class 1. Turbellaria – Dugesza, Planaria; Class 2. Trematoda – Fasciola (liver-fluke), Schistosoma (blood-fluke); Class 3. Cestoda – Taenza solium (pork tape-worm)