PHYLUM PRIAPULIDA (priapos, phallus, Creek god of reproduction symbolized by the penis)

1. Habitat: The priapulids are a small group. It has only 16 species of marine worms found in cold waters. They lived in the mud of sand or seafloor. They feed on small annelids and other invertebrates. Priapulus cuudalus is most common specie.

2. Body form and size: The priapulid body is cylindrical in cross section. They range inlength from 2 mm to about 8 cm.

3. Body parts: The anterior part of the body is introvert(proboscis).
They can draw this introvert into longer posterior trunk. The muscles introvert is surrounded by spines. It is used for burrowing.

4 Body wall: A thin cuticle covers the body. This cuticle has spines. The trunk bears superficial annuli.

5. Pseudocoelom: A straight digestive tract is suspended in a large pseudocoelom. Pseudocoelom acts as a hydrostatic skeleton. In some  species, the pseudocoelom contains Excretory amoeboid cells. These organ cells are used for transport of  gas.

6. Nervous system: The nervous system consists of a nerve ring around the pharynx and a single midventral nerve cord.

7. Reproduction: The sexes are separate. A pair of gonads is suspended in the pseudocoelom. It shares a common duct with the protonephridia. The duct opens near the anus and gametes are shed into the sea. Fertilization is external. The eggs finally. sink to the bottom. Here larvae develop into adults. The Cuticle is repeatedly molted throughout life.




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