1. 5. Molluscs

2. Phylum Mollusca 200,000 species
More species in ocean than any other animal group
Soft body enclosed by calcium carbonate shell
Body covered by mantle
Thin layer of tissue that secretes the shell

3. Phylum Mollusca Displays Bilateral Symmetry
Ventral muscular foot used for locomotion
Most had have that includes eyes and other sensory organs

4. Essentially, a mollusc is a coiled mass of vital organs wrapped
in a dorsal shell.

5. Phylum Mollusca Some have radula
Ribbon of small teeth used to rasp food from surfaces
Made of chitin

6. What’s a radula and how does it work? Modern woodworkers could tell you!
micrograph of a mollusc radula: note the
chisel-like design

7. Phylum Mollusca Have paired gills
Portion of body may be coiled and asymetrical
Occupy all marine environments – rocky shores to hydrothermal vents

8. Essentially, a mollusc is a coiled mass of vital organs wrapped
in a dorsal shell.

9. Gastropods (Class Gastropoda), or stomach foot,
are the most common mollusks.
Snails, limpets, abalone, and nudibranchs.
75,000 spp.
red abalone
Haliotis rufescens
giant keyhole limpet
Megathrua crenulata
Cooper’s nutmeg snail
Cancellaria cooperi
nudibranch, Phidiana crassicornis
Cone snail, Conus geographus

10. Class Gastropod – Stomach Footed
Coiled mass of vital organs enclosed by a dorsal shell resting on a foot

11. Class Gastropod – Stomach Footed
Most use radula to scrape algae
Mud snails are deposit feeders
Whelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishes
Modified Radula to drill and rasp prey

12. Class Gastropod – Stomach Footed
Nudibranchs (sea slugs)
No shell
Colorful branches of the gut and gills
Prey on sponges and other invertebrates
Produce noxious chemicals or retain undischarged nematocysts taken undigested from prey

13. Bivavles: Class Bivalvia

14. Class Bivalvia Clams, mussels, and oysters
Body laterally compressed and enclosed with two parts (valves)
No head or radula
Gills expanded and folded used to obtain oxygen, and filter and sort food particles from water

16. Scallops also filter feed. Many have striking color patters.

17. Class Bivalvia
Inner surface of shell lined w/ mantle so whole body lies in mantle cavity
Strong muscles used to close valves

18. Class Bivalvia
Clams burrow in sand or mud and water drawn in and out of mantle by siphons
Allow clam to feed and obtain oxygen while buried

19. Class Bivalvia
Mussels secrete byssal threads that attach them to rocks and other surfaces

20. Class Bivalvia
Oysters cement their left shell to hard surface and other to another oyster
Pearls occur when irritating particles are lodged within the mantle cavity and covered by secretions (CaCO3) from oyster

21. Class Bivalvia
Some scallops can swim by rapidly ejecting water from mantle cavity with siphon

22. Class Bivalvia Shipworm bores in mangroves, driftwood, and pilings
Have symbiotic relationship w/ bacteria in the gut that digests wood
Valves lie at the inner end of tunnel lined w/ calcium carbonate and siphon protrudes from entrance
Fouling organism = settles on bottoms of boats, pilings, and other submerged surfaces

23. “Putting Your Head and Feet Together”
Cephalopods
“Putting Your Head and Feet Together”

24. Class Cephalopoda (head footed)
Predators specialized in locomotion
Octopi, squid, and cuttlefish
Agile swimmers w/ complex nervous system and reduction or loss of shell
All are marine

25. Cephalopod (General Morphology)
While still following the basic body plan of a mollusc, octopi
are highly specialized.

26. Cephalopod (General Morphology)
Large eyes on side of head
Thick muscular mantle which protects head
Water enters mantel and leaves through siphon = jet propulsion

27. Cephalopod: Octopi Octopi Eight long arms (2 in to 30 feet)
Bottom dwellers that live in crevices, bottles, etc
Have beak-like jaws and radula to rasp flesh and secrete paralyzing substance
Distract predators with dark fluid from ink sac

28. Cephalopod: Squid Squid
Two triangular fins on mantle – better swimmers than octopi
Can remain motionless, move forward, or backward
Eight arms and two tentacles, all with suckers
Has pen in upper surface of mantle
Few cm to 60 feet!!

29. Cephalopod: Cuttlefish
Eight arms and two tentacles, but body flatten w/ fin running along the body
Have calcified internal shell aids in buoyancy

30. Cephalopod: Chambered Nautilus
Coiled external shell containing gas filled chambers serves as buoyancy organ
Has suckerless tentacles

31. Other Molluscs Chitons (class Polyplacophora – bearer of many plates)
All marine
Eight overlapping shell plates covering dorsal surface
Live in shallow hard bottoms
Have radula to rasp algae

32. Other Molluscs Tusk shells or scaphopods (class Scaphopoda)
Elongated shell tapered at end resembling elephant tusk
Sandy muddy bottoms in deep water
Many species have thin tentacles to capture small prey
Tusk shell hermit crab

33. Biology of Molluscs: Nervous System
Gastropods and bivalves have ganglia (local brains) located in different parts of body

34. Biology of Molluscs: Nervous System
Cephalopods
Most complex of invertebrates
Brains coordinate and store information
Complex eye reflects development
Octopi and cuttlefish can learn

35. Biology of Molluscs: Nervous System
Cephalopods
Display rapid color change coordinated with behaviors and moods, from sexual display to camouflage
Cuttlefish “flash lights” while octopi change color and behavior to mimic poisonous fish and sea snakes

36. Biology of Molluscs: Reproduction and Life History
Most have separate sexes (some hermaphroditic)
Bivalves, chitons, tusk snails, and some gastropods release sperm and egg into water
Cephalopods and most gastropods – internal fertilization

37. Biology of Molluscs: Reproduction and Life History
Cephalopods – modified arm to transfer spermatophore
Develop in yolk-filled eggs attached to crevices
Female dies – guarding eggs = no food
Some have trochophore larvae, displaying relationship to segmented worms

38. Kings of Camouflage