MOLLUSCA Description: Bilaterally symmetrical. Body has more than two cell layers, tissues and organs. Body possesses a through gut with mouth and anus. Has a nervous system with a circum-oesophagal ring, ganglia and paired nerve chords. Has an open circulatory system with a heart and an aorta. Has gaseous exchange organs called ctenidial gills. Has a pair of kidneys. Examples 1. Octopus vulgaris - Common Octopus 2. Stagnicola elodes - Marsh Pondsnail