1. Zoology Rainier Jr/Sr High School Mr. Taylor
Phylum Mollusca
Zoology
Rainier Jr/Sr High School
Mr. Taylor

2. Mollusks Kingdom Animalia Mollusca means “soft body” Phylum Mollusca
Live in a variety of habitats; marine, freshwater, and land species.

3. Mollusca characteristics
Bilateral symmetry
Have a true coelom
Body plan: 3 parts
Head/foot: mouth, sensory organs, motor organs.
Visceral mass: digestive, excretory, respiratory, circulatory, and reproductive organs
Mantle: surrounds visceral mass & secretes the shell (if present)

4. Mollusca characteristics
Shells: mollusks have zero, one, or two shells
Shell is made of protein and often hardened by calcium carbonate.
The shell can be internal or external.
Radula: all mollusks except bivalves have a rasping tongue called a radula

5. Class Bivalvia The “classic” bivalves are clams, oysters, and scallops
Bivalves have
2 external shells
no distinct head region
no radula
few sensory organs

6. Clams Have typical bivalve anatomy
Possess a few light and touch sensors on edge of shells
Circulatory system is open and utilizes a 3 chamber heart
Clams have separate sexes

7. Clams Have an incurrent and excurrent siphon
Incurrent siphon pulls water into the clam’s shell and over the gills:
O2 and CO2 exchange
Gills are covered with mucus and traps food particles as water flows over the gills. Cilia move food to mouth then on to stomach, intestines, and out anus.

8. Clams

9. Scallops Scallops have “eyes” along the edge of their shells
Non-visual photosensors
Can detect movement by sensing light and dark passing from one sensor to another.
Scallops move by forcefully closing their shells and ejecting water.

10. Scallops

11. Oysters Oysters are the sessile bivalves.
As with other mollusks, the larval stage is a free-swimming trochophore and serves as a dispersal mechanism.

12. Class Gastropoda Gastropoda means “belly foot”
This class is where we find snails and slugs.
One shell
Snails have an external shell
Some slugs have an internal shell

13. Snails Bilateral symmetry, but many are coiled.
Have a nerve system with 6 ganglia.
Photosensors on “eyestalks” detect light and shadows.
Have an open circulatory system.
Sexual reproduction with internal fertilization.

14. Snails
Respire using gills. Land-based snails must keep them moist: limits territory.
See text page 661 to see where the gills are located under their shell.
Movement by using cilia on bottom of foot
Secrete mucus to glide on
Provides protection of foot
Gives traction so snails can climb smooth, vertical surfaces

15. Snails

16. Slugs and Nudibranchs
Slugs have either no shell (most) or an internal shell (only a few)
Live in moist environments as they need to keep their skin moist to allow for respiration.
Nudibranchs are special sea slugs
They have no shells, gills, or mantle
Have decorative plumes on their backs that increase skin surface area to allow for gas exchange.

17. Slugs and Nudibranchs

18. Class Cephalopoda Cephalopoda means “head foot”
Octopus, squid, nautilus, and cuttlefish
Characteristics include
Very well-developed head and tentacles
Shell
Nautilus has an external shell
Cuttlefish and squid have an internal shell
Octopus have no shell

19. Class Cephalopoda Characteristics include Closed circulatory system
Well-developed nervous system with a complex brain!
Have jaws with a radula and beak
All are predators!

20. Octopus Jet propelled using an excurrent siphon
They have no shell and are extremely agile
Large eyes are image forming.
Suckers on tentacles not only grasp but have chemosensors and tactile (touch) sensors to locate prey.
Sexes are separate and females will brood eggs (she cares for them and keeps predators away)
Have the ability to change colors (camouflage)

21. Octopus

22. Squid
Very similar to octopus with 2 more, but less-developed, tentacles.
Not as agile
Have an internal shell
Giant squid in excess of 20 feet long have been found.
As do octopus and cuttlefish, squid use “ink” as a defense mechanism

23. Squid

24. Nautilus Have an external shell with chambers
Secretes shell as it grows, chambers become progressively larger.
Live in outermost chamber.
Uses shell for buoyancy: deep ocean by day, comes to shallow depths to feed at night.

25. Nautilus

26. Cuttlefish
Ink has been used as a paint pigment for centuries.