5. Molluscs

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
Whats a radula and how does it work? Modern
woodworkers could tell you!
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.

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

15
(No Transcript)
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
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

• 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

• 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

http//www.sciencefriday.com/video/08/05/2011/wher
e-s-the-octopus.html
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

• http//www.youtube.com/watch?vIn7n590GjxU