biology 27.3
TRANSCRIPT
27-3 Annelids
Septum
• Internal wall between the segments of an annelid’s body
Seta
• Bristle attached to the segments of many annelids
crop
• In earthworms, part of the digestive system in which food can be stored; in birds, structure at the lower end of the esophagus in which food is stored and moistened.
gizzard
• In earthworms, part of the digestive system in which food is ground into smaller pieces; in birds, a muscular organ that helps in the mechanical breakdown of food
Closed circular system
• System in which blood is contained within a network of blood vessels.
Gill
• Filamentous organ in aquatic animals specialized for the exchange of gases with water.
nephridium
• Excretory organ of an annelid that filters fluid in the coelom
Clitellum
• Band of thickened, specialized segments in annelids that secretes a mucous ring into which eggs and sperm, are released.
Key Concept
• Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm.
Key Concept
• Oligochaetes are annelids that typically have stream-lined bodies and relatively few setae compared to polychaetes. Most oligochaetes live in soil or fresh water.
Key Concept
• Leeches are typically external parasites that suck the blood and body fluids of their host.
Key Concept
• Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae.