ZOOLOGY: STUDY GUIDE - Ye. O. Nevedomska - 2013

LECTURE 10. PHYLUM ANNELIDA, or SEGMENTED WORMS (Annelida)

2. Evolutionary Advancements of the Phylum Annelida

The progressive evolutionary Features of the phylum Annelida include:

1) The Emergence of a secondary body cavity, or coelom, lined with its own epithelial walls;

2) segmentation of the body into metameres containing repeating internal organ structures (metamerism);

3) further advancement of The Nervous system: a significant enlargement of the cerebral ganglion, The formation of a circumoesophageal nerve ring, and a ventral nerve cord resulting from the fusion of lateral Nerve Trunks and The Development of ganglia in each segment;

4) the appearance of a Circulatory system, as well as dermal gills in the Respiratory system, which substantially increased The rate of METABOLISM;

5) greater complexity of the Digestive System (Differentiation of the midgut into specialized regions, allowing for continuous Digestion);

6) the development of paired body outgrowths on each trunk segment — parapodia (from the Greek para — beside, and podion — FOOT), which function as locomotory Organs;

7) the formation of a multicellular excretory system — metanephridia, occurring as a pair in each body segment.