Chapter 27 Mollusks and Segmented Worms Both are

Chapter 27 Mollusks and Segmented Worms Both are from the kingdom Animalia

Mollusks (phylum: Molluska) • Animals that live or once lived in a shell • Include animals like snails, oysters, squids, slugs

Common characteristics of all mollusks: • • • Bilateral symmetry Have coelem (cavity around organs) 2 body openings Muscular foot- movement Most live in marine Or freshwater • Mantle-thin membrane around organ • Has gills

3 classes of mollusks: 1. bivalves- have 2 shells -Filter feed using a siphon -Large ligament that holds shell together -open circulatory system- blood pools around organs (no vessels)

Mollusk classes cont… • 2. gastropods- have 1 shell – Have a structure called a radula that is used to feed – Radula-tongue-like structure with rows of teeth used to scrape food – Open circulatory system- blood moves in open spaces around organs

Mollusk classes cont… • 3. cephalopods- in octopus and squid • Capture food with tentacles • Has sharp beaked jaws that tear food • Closed circulatory system- has vessels that hold blood • Has a reduced internal shell • Release a dark substance called ink to cloud water to escape danger

Segmented worms • Kingdom-animalia • Phylum-Annelida • Includes bristleworms, earthworms, leeches

Segmented worm characteristics • Have tiny segments/rings – Each has its own muscles – Allows movement by shortening and lengthening • Bilateral symmetry • Coelem-cavity around organs • 2 openings (mouth and anus) • Nocturnal-feed at night

Earthworm structures: Mouth-takes in food Crop-stores food until it can be broken down Gizzard-has stone-like structures that grind up soil/food until tiny pieces can be absorbed by the intestines Nephridia-structures that eliminate waste found on each segment Setae-tiny hairs that extend from each segment – Anchors worm

Earthworm structures • Nervous system- each segment has nerves that lead to a nerve cord • The nerve cord is on the ventral side • Clitellum- structure where worms mate (copulate) • Reproductive structuresearthworms have both sex organs (hermaphrodites) – Eggs are fertilized internally – Eggs are released in a protective structure called a capsule Circulatory system- includes heart, vessels, and blood