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Phylum: Mollusks. Three Classes of Mollusks. Class Gastropoda – snails, slugs Class Bivalvia – clams, oysters, mussels, scallops Class Cephalopoda –  octopi, squids and cuttlefishes. Basic information. Over 100,000 living species Marine, fresh water, and land Most Bilateral symmetry.

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three classes of mollusks
Three Classes of Mollusks
  • Class Gastropoda – snails, slugs
  • Class Bivalvia – clams, oysters, mussels, scallops
  • Class Cephalopoda –  octopi, squids and cuttlefishes
basic information
Basic information
  • Over 100,000 living species
  • Marine, fresh water, and land
  • Most Bilateral symmetry
body plan
Body Plan
  • Divided into two regions:
  • head/foot
  • visceral mass
head foot
  • Head (contains mouth and variety of sensory structures)
  • Foot (muscular organ used for locomotion)
visceral mass
Visceral Mass
  • heart
  • digestion
  • excretion
  • reproduction
  • Covers and protects the visceral mass
  • Secretes shell
mantle cavity
mantle cavity
  • Location of gills
  • Space between the mantle and the visceral mass
nervous system
nervous system
  • Ganglia: paired cluster of nerve cells
  • locomotion
  • feeding
  • process sensory information (light, touch)
  • Radula: flexible, tongue like strip of tissue covered with tough abrasive teeth that point backward
basic information1
Basic Information
  • Most diverse class of mollusks
  • 90,000 species
  • Snails, abalones, conches= single shell
  • Slugs and nudibranchs= no shell
  • Visceral mass twists around 180° in relation to the head
  • Twisting results in mantle cavity, gills, and anus to the front of the animal
  • Gastropod is now able to with drawl its head into mantle cavity when threatened
  • foot secrets a substance allowing animal to glide over surfaces (Slime Trail)
open circulatory system
Open circulatory system
  • HEMOLYMPH (blood in an organism with open circulation) does not remain in vessels
  • Collected from gills or lungs
  • Pumped through heart
  • Released directly into spaces in the tissues
      • Fluid filled spaces or blood cavity
bivalvia clams

Bivalvia: Clams

Other Bivalvia: scallops, mussels, oysters

  • Sessile
  • Filter feeders
  • No radula
  • No cephalization
  • Aquatic
anatomy of valves
Anatomy of Valves
  • Shell is divided into two halves (valves)
  • Connected by a hinge
  • Adductor muscles
    • Contract: close valves
    • Relax: open vlaves
clam sensory information
Clam Sensory information
  • 3 pairs of ganglia
    • mouth (cerebral)
    • digestive system (visceral)
    • Foot (pedal)
  • Foot helps burrow in the sand or mud
water flow
Water flow
  • water enters through incurrent siphon
  • Water exits through excurrent siphon
steps in digestion filter feeders
Steps in digestion: Filter Feeders

1. Cilia in gills set up water current

2. Gills filter water for small organisms

3. Palps: flaplike structures that surround & guide food into the clam's mouth

4. Food then enters the mouth

steps in digestion filter feeders1
Steps in Digestion: Filter Feeders

4. Stomach: Digestion begins

5. Digestive glands: digested particles are absorbed

6. Intestines: collects and removes digestive wastes

7. Waste are passed through the rectum and excreted through anus

function of gills
Function of Gills
  • Trap food particles
  • Exchange oxygen and carbon dioxide
growth rate
Growth rate
  • Umbo oldest part of the clam
  • Growth rings
cephalopod head foot
Cephalopod “Head-foot”
  • foot is concentrated in the head region
  • foot is modified into arms and tentacles equipped with suckers
  • Foot also forms funnel (siphon) for expelling water, allowing movement by "jet propulsion"
the major distinction between the squid and octopus
The major distinction between the squid and octopus

Squid Suction Cups

Squid suction cups are armed with hooks or sucker rings (or a combination of

the two). Octopus have simple suction cups without secondary armature.

Tentacle club of Architeuthis, showing circular-saw-like sucker rings.

tentacle club of Mesonychoteuthis, with swiveling hooks.


Profile of Mesonychoteuthis tentacle club, showing hooks.

Suction cups of Haliphron atlanticus, the giant gelatinous octopus (the world's largest species of octopus), lacking secondary armature.

giant squid
Giant Squid

Can reach length of up to 60 feet and weight of more than 3.5 tons.

Architeuthis dux

  • Jet propulsion by using siphon to force water out
  • Crawling – octopus

*Also uses siphon

external features
External Features
  • Octopus: 8 arms with either one or two rows of suction cups (but never hooks or sucker rings),
  • Squid/cuttlefish: 10 appendages containing suction cups (contain either hooks or sucker rings)
      • 8 arms
      • 2 tentacles
  • All except nautilus have ink sack which empties into rectum; ink contains the pigment melanin (same pigment as human skin)
  • Released when the animal is alarmed. The animal quickly departs from the scene leaving the ink as a decoy to the predator.
color changes
Color Changes
  • Chromatophores – pigment cells that expand and contract to produce color change.
    • Used as danger signals, protective coloring, and for courtship.

The Blue Ringed Octopus (found in shallow coral and rock pools of Australia): It’s poisonous saliva is 10,000 more potent than cyanide. This octopus is only the size of a golf ball but carries enough poison to kill 26 humans in minutes.


Fish, other mollusks, crustaceans, worms

Beak like jaws and radula tear prey into pieces

Octopus and Cuttlefish have poison in saliva

  • Closed circulatory system
  • Blood delivers oxygen and nutrients directly to organs through veins and arteries
nervous system1
Nervous System
  • Well-developed brain; eyes which are similar in construction to vertebrate eyes
  • FYI: The giant squid has the largest eye of any animal, either living or extinct. In a 55-foot specimen the diameter was 15.74 inches. In comparison, a blue whale's eye has the diameter of 4.70 inches, and humans have an eye diameter of .94 inches.
  • Male or Female
  • The male uses arm to take sperm from own mantle cavity and insert into females mantle cavity
  • The female lays ~100 eggs and guards them until they hatch (approx 50 days)
  • Frequently the mother dies soon after the eggs hatch because during the guarding of the eggs she is unable to eat. 