Marine Mollusks

Overview of the classes of marine mollusks.

1. Mollusca
Marine Science
Module 4 ~ Unit 4

2. Mollusca
•Mollusk characteristics
overview
•Characteristic differences
•Assignment 4.4.1
•Classes: Bivalves, Gastropods,
and Cephalopods
•Other Classes
•Assignment 4.4.2

3. Characteristics Overview
•Cephalization: (Has a definite head/nervous system)
•Body cavity has definitive digestive/intestinal system
•Has an excretory system with kidney or
nephridium (tube-like organ)
•Open circulatory system with heart
•Gills for respiration
•Muscular foot used for movement
•Some have protective shell over soft body

4. Which ones are mollusks?

5. They all look so different!
How can they all be mollusks?

6. Differences of Characteristics
•Cephalization
•“Head” means they have
eyes, mouth, and a brain…
not necessarily the way we
might imagine a head looking

7. Differences of Characteristics
•Most mollusks have a
radula (like a cat’s tongue)
Fresh water pond snail cleaning algae off glass.
Radula of squid

8. Differences of Characteristics
•Most have a muscular foot for movement
–When you eat clams and scallops you’re eating the foot

9. Differences of Characteristics
•She sold sea shells by the sea shore. 
•Some mollusks have a two part shell, some only
one, and some don’t use shells on the outside

10. Any questions so far?

11. Bivalves ~ Gastropods ~ Cephalopods
•Bi (two) valves
–Don’t have radula… they filter feed
–Giant Killer Clams
•Gastro (stomach) pods (foot)
–a.k.a. snails and slugs
–Nudibranchs
•Cephalo (head) pods (foot)
–Don’t have shells (exception is the Nautilus)

12. •More on these in a moment…
Bivalves ~ Gastropods ~ Cephalopods

13. Assignment 4.1.1
•Create a PowerPoint presentation that identifies and
illustrates the various characteristics of mollusks.
•Include habitat, what they feed on and examples and
specific explanations of the three groups of mollusks.
•Your presentation must be no longer than 7 slides.
•Make sure you give credit for any graphics that are not
your own. Include a reference list at the end.
•You should have at least 3 credible reference sites.
Contact your instructor to discuss what a "credible
reference site" is. (REQUIRED CONTACT).

14. Mollusca
Marine Science
Module 4 ~ Unit 4
..Continued..

15. Pelecypoda

16. Pelecypoda
•A.K.A. the bivalve class
•2 shell halves
•Filter feeders (no radula)
•Shell secreted by the mantle
•Have 2 siphons for pulling in & pushing out water
•Some have eyes (scallops)

18. Pop Quiz
How many siphons does a bivalve
have?

19. Clam buries itself:
http://www.youtube.com/watch?v=mWs-zAd1avM&feature=related

20. Gastropoda
•A.K.A. abalones, snails, and slugs
•One shell with an operculum (door)
•Has head with eyes and radula
•One group does not have shell (nudibranchs)
•Gastropod fossil link from Angel
–http://www.oum.ox.ac.uk/thezone/fossils/inverts/gastro.htm

22. Which of the following mollusks are
not part of the gastropoda class?
Snails
Squids
Abalones
Slugs

23. Conch

24. Cephalopoda
•A.K.A. squid, octopus, nautilus
•Only the nautilus has an external shell
•Octopus and squid have 8 tentacles
(squid and cuttlefish have 2 additional longer tentacles)
•Well-developed eyes and brain

26. Octopuses or Octopi?
Many people get confused about the proper plural for the
word octopus. Octopus is frequently given a Latin plural, yet
the word derives its second root from Greek, not Latin (the
english "foot" root from Latin is "pod" or "ped", while from
Greek it is "pus"). What is the proper plural, anyway? Many
say "octopi." The singular looks like a Latin masculine
singular, ending in "us," but it really isn't, so pluralizing it to
"octopi" is not correct. Most people also mispronounce it as
well. If it were "octopi," it would be pronounced "octo-pee" not
"octo-pie," and that sounds silly! So, the correct plural is
"octopuses," believe it or not. I prefer not to use either of
them. Every time you say "octopuses" someone will correct
you, and you end up in an argument. So I like to use
"octopods," which is the proper plural of the taxonomic order
Octopoda, containing the eight-armed cephalopods.

27. Pelecypoda

28. Polyplacophora (chitons)- 8-plated shell
Monoplacophora
Scaphopoda- A.K.A. tusk shells

29. Any questions?

30. Assignment 4.4.2
•Part 1: Prepare a chart that compares and
contrasts all groups of mollusks. Your chart should
cover all the 7 characteristics of mollusks, as well
as provide a list of common named species for each
group. Include habitat and feeding strategies for
each group.
•Part 2: Choose one organism from each group of
mollusk that you find interesting. Prepare a fact
sheet for each organism. The fact sheet should
include as much detail as possible related to the
critter. Graphics (i.e., pictures of critter and habitat,
relationships with other critters, drawings of lifecycle
and/or anatomy, etc. ) will enhance your fact sheet.

31. See Characteristics Overview
Slide in the beginning for 7 characteristics