1. Mollusks and Echinoderms
Section 1 – Mollusks (Gastropods, Bivalves, and Cephalopods)
Mrs. Donna Gentile – September, 2014

2. Characteristics of Mollusks
Examples: clams, oysters, scallops, snails, squids
Invertebrates with soft, unsegmented bodies that are often protected by a hard outer shell.

3. Characteristics of Mollusks – cont.
Thin layer of tissue called a mantle that covers its internal organs
Biologists classify mollusks into groups based on their physical characteristics: shell, type of shell, type of foot, type of nervous system

4. Body Structure
Bilateral symmetry
Digestive system with 2 openings
Body parts are not repeated – internal organs are located together in one area

5. Circulatory System
Most have an open Circulatory System – blood is not always inside blood vessels
Blood sloshes over the organs and returns to the heart

6. Obtaining Oxygen Most mollusks that live in water have gills
Gills have cilia and a rich supply of blood vessels
Carbon dioxide, a waste gas, moves out of the blood and into the water

7. Snails and Slugs Gastropods are the largest group of mollusks
Live in oceans, rocky shores, fresh water, on land
Have a single external shell or no shell at all

8. Obtaining Food Some are herbivores, scavengers, carnivores
Use a radula to obtain food
Herbivores – sandpaper to tear through plant tissue
Carnivores – drill a hole, scrapes

9. Movement
Creeps along on a broad foot
Foot oozes a carpet of slippery mucus which helps make it easier for the gastropod to move

10. Two-Shelled Mollusks
Bivalves – are mollusks that have 2 shells held together by hinges and strong muscles
Examples: oysters, clams, scallops, mussels
Found in all kinds of watery environments

11. Obtaining Food Filter feeders that strain tiny organisms from water
Capture food as water flows over their gills, food sticks to the mucus that covers the gills, cilia move the food particles into it’s mouth
Most bivalves are omnivores

12. Movement Don’t move quickly
Larvae – float or swim Adults – stay in 1 place or use their foot
Oysters and mussels attach themselves to rocks
Clams move

13. Protection
Sand gets stuck between a bivalve’s mantle and shell – it irritates the soft mantle – mantle produces a smooth, pearly coat to cover the object
Sometimes a pearl forms

14. Octopuses and Their Relatives
Cephalopods are ocean-dwelling mollusks whose foot is adapted to form tentacles around its mouth.
Examples are:octopuses, squid, nautiluses, cuttlefishes

15. Obtaining Food
Carnivores - uses tentacles to capture the food and crush it
Tentacles have suckers that receive sensations of taste and touch
It doesn’t have to touch something to taste it because the suckers respond to chemical in the water – tastes before touching it

16. Nervous System Large eyes – excellent vision
Most complex nervous system of any invertebrate
Large brains – can remember and learn

17. Movement Swim by jet propulsion
Squeeze a current of water out of the mantle cavity and through a tube
Turning the tube changes the direction they’re going

18. Echinoderms Section II

19. Characteristics of Echinoderms
Examples: Starfish, sea cucumber, sea urchins
Marine dwelling
Invertebrates
Spiny skin
Able to REGENERATE – regrow missing parts

20. Body Structure
Endoskeletons
Penta-radial symmetry

21. Circulatory System
Network of fluid-filled canals that function in gas exchange, feeding and in movement.
Contains a central ring and areas which contain the tube feet The tube feet poke through holes in the skeleton and can be extended or contracted.
They do not have a true heart and the blood often lacks any respiratory pigment (like hemoglobin).

22. Obtaining Oxygen
Echinoderms have a a poorly developed respiratory system.
They use simple gills and their tube feet to take in oxygen and pass out carbon dioxide.

23. Obtaining Food Majority are carnivores – feed on sponges & mollusks
Stomach is flipped out of mouth and surrounds soft body parts of prey. Digestive juices are secreted and liquefy prey.
Mouth, stomach, digestive gland & anus

24. Movement
When echinoderms move in a manner such as walking or crawling, they pump sea water through a series of internal body canals.
The water is used to inflate some of the tube feet, causing them to expand. In many species, the tube feet are equipped with suckers that grip onto the sea floor.
The feet hold tight to the bottom as muscles within the feet contract, enabling the animal to propel itself.”

25. Nervous System
Echinoderms do not have brains, they have nerves running from the mouth into each arm or along the body.
They have tiny eyespots at the end of each arm which only detect light or dark.
Some of their tube feet, are also sensitive to chemicals and this allows them to find the source of smells, such as food.