Mollusks and Annelid Worms 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 Pumping Blood 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.