BIOLOGY Volume 1 - A Guide to General Biology - 2004

8. HETEROTROPHIC NUTRITION

8.2. Feeding Mechanisms in Animals

8.2.1. Filter feeding

Animals that feed in this manner are known as filter feeders; they strain small particles of organic matter from the Water. This mode of feeding is common among many Molluscs, such as the common mussel (Mytilus edulis), which attaches itself to rocks and stones in shallow coastal waters (Fig. 8.5). The mussel is a bivalve mollusc. The shell of these molluscs consists of two halves, or Valves, joined together. Inside the shell lie two large gills, one on each side. The gills are covered in fine Hair-like structures called cilia. The beating of the cilia creates a current of water that enters the animal through a tube called the incurrent siphon and leaves via a tube called the excurrent siphon (Fig. 8.5). This water carries the food required by the mussel, such as microscopic Protozoans and Algae. Numerous secretory Cells interspersed among the cilia produce streams of sticky mucus that trap food particles. This food is then moved by tracts of specialized cilia toward the Mouth, which is located near the anterior edge of the gill. The mouth is surrounded by specialized structures, also covered in cilia, where food particles are sorted before entering the mouth. The digestive tract of the oyster consists of a Stomach and a short intestine, terminating in an anus located near the excurrent siphon.

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Fig. 8.5. Filter-feeding mechanism in the mussel (Mytilus edulis).