Characteristics
- Metameric Body
- Bilateral symmetry
- Spiral cleavage
- Trochophore larvae
- Schizocoelous coelom formation
- Paired, epidermal setae (chaetae)
- Closed circulatory system
- Dorsal suprapharyngeal ganglia and ventral nerve cords with ganglia
- Metanephridia (usually) or protonephridia
Relationships to Other Animals
Part of the lophotrochozoan branch of the animalia. Annelids and arthropods are closely related phylogenically. Mouth first from blastopore. These two groups also share segmentation. Annelida are typically divided into two classes and have three other groups of wormlike animals that have been considered separate phyla (Sipuncula, Echiura, and Siboglinidae). This phyla orignated from the precambrian times.
Metamerism
Earthworms are irganized into ringlike segments. The internals are divided into segments and this is called metamerism. This influences the annelid's structure and function. This compartmentalization of the body results in each segment with its own excretory, nervous, and circulatory structures. Metamerism may have developed in conjunction with blood circulation to segmental appendages of marine worms (Polychaeta).
Metamerism adaptive features is flexible support efficient locomotion. During embryonic development their mesoderm splits on eitgher side of the embryonic gut tract. E
Metamerism adaptive features is flexible support efficient locomotion. During embryonic development their mesoderm splits on eitgher side of the embryonic gut tract. E