Chapter 15.2 Mollusks and Annelid Worms
Mollusks • Snails, slugs, clams, oysters, squids and octopuses are all mollusks • Most mollusks fit into 3 classes • Gastropods which include slugs and snails • Bivalves which include clams and other shellfish that have 2 shells • Cephalopods include squids and octopuses
How do mollusks eat? • Each mollusk has its own way of eating. • Snails and slugs eat with a ribbon like organ – a tongue covered with curved teeth. This organ is called a radula. • Clams and oysters attach to one place and use gills to filter tiny plants, bacteria and other particles from the water. • Octopuses and squids use tentacles to grab their food and to place it in their powerful jaws.
Ganglia and Brains • All mollusks have complex ganglia. • They have ganglia to control breathing, movement and digestion. • Pumping Blood • Unlike simple invertebrates mollusks have a circulatory system. • Open-circulatory system: a simple heart pumps blood through blood vessels that empty into sinuses or spaces in the animals body. • Closed circulatory system: a heart pumps blood through a network of blood vessels that form a closed loop.
Mollusk bodies • While mollusks may look very different from each other, their inner structures are actually very similar. • Foot : helps the animal move • Visceral mass: the gills, the guts, and other organs • Mantle: a layer of tissue that covers and protects the visceral mass • Shell: the outside of the mantle. Protects the mollusk from predators
Annelid Worms • Often called segmented worms because their bodies have segments • A segment is an identical or almost identical repeating body part. • Like roundworms and flatworms annelid worms have bilateral symmetry. • Annelid worms are more complex than other worms • They have a closed circulatory system • They have a complex nervous system with a brain • A nerve cord connects each segment to a ganglion in the brain
Three Major Groups of Annelid Worms • Earthworms: Earthworms are the most familiar • Each earthworm has 100 to 175 segments • Each segment has a special job • Earthworms eat material in the soil. They break down plant and animal matter in the soil and leave behind wastes called castings. • They also improve garden soil by creating tunnels that allow air and water to reach deep into the soil • To move earthworms use stiff hairs or bristles to move through the dirt
Marine Worms • These worms are called polychates(which means many bristles) • They also come in many bright colors • Most live in the ocean
Leeches • Known as parasites that suck other animals blood. • Some are not parasites, these eat dead animals • They can be useful to help restore blood flow to a limb and to also prevent blood clots.