Minor Eucoelomate Phyla

Abstract

A convenient grouping of Eucoelomata in which:-

• 1. The body is not metamerically segmented at least in the adult, but may be annulated.

• 2. There is no distinct head, although a prostomium or proboscis may be present. The body is often worm-like

• 3. The gut is straight, coiled or U-shaped.

• 4. The nervous system is simple: a cerebral ganglion may be present or absent; a circum-oesophageal ring connects with a single ventral nerve cord which may or may not be ganglionated.

• 5. Organs of special sense are usually lacking.

• 6. The epidermis may be covered with a thin cuticle or it may secrete a shell or tube around the body.

• 7. Appendages are generally lacking, although tentacles or spines are sometimes present anteriorly.

• 8. The body usually contains circular and longitudinal muscles, but these may be lacking in certain Bryozoa. Circular muscles are lacking in the Chaetognatha.

• 9. A coelom is present and is often subdivided into distinct regions.

• 10. Excretory organs may be present or absent. When present they are of the nephridial type.

• 11. Blood vascular system is often reduced or lacking. When present it is of the closed type.

• 12. The products of the gonads are passed to the exterior through nephridia or via the coelom through gonoducts.

• 13. The sexes may or may not be separate.

• 14. Larval forms of various kinds occur, some of which resemble trochophores.