Phylum Mollusca

Phylum Mollusca

• Bilateral symmetry• Body Cavity - Coelomate• Body has three distinct regions

– Visceral mass - central section, which contains the body's organs

– Mantle - Means “cloak” in Greek. Wraps around the visceral mass, secretes shell. Mantle cavity -space between mantle & visceral mass.

– Foot - Ventral, muscular and prominent. • Functions:

– Locomotion - Bivalvia use to dig into sand– Securing food - modified into a tentacle in

Cephalopods

Digestive System

• Radula - rasping organ in Gastropods, Beak in CephalopodsAll mollusks except Bivalvia have this structure.

• Used to scrape algae off rocks (Gastropoda) or as a weapon to puncture holes in prey (Cephalopoda)

• Has mouth, esophagus, stomach, intestine and anus.

• Digestive gland secretes enzymes into the gut.

Excretory System

• Nitrogenous wastes dumped into coelom. Cilia in nephridium cause fluid (wastes and nutrients) to move through nephridia.

• Nutrients are reabsorbed; wastes empty into the mantle, then removed.

Circulatory System

• Open system for all except Cephalopoda.

• Dorsal aorta - Coelom - restricted to the region around the Dorsal Aorta.

Respiratory System

• Gills located in their mantle cavity• Cilia beat continuously causing a

steady stream of water to pass over the gills. Gills also trap food

Nervous System

• Ring of nervous tissue around esophagus

• Two sets of ventral nerve fibers• Nerve fibers maybe quite large -

squid• Photoreceptors, Chemoreceptors

and tactile receptors

Reproductive System

• Male and female• External fertilization

Major Classes

• Class Gastropoda • Class Bivalvia • Class Cephalopoda • Class Polyplacophora• Class Scaphopoda • Monoplacophora - Primitive

Class Gastropoda - Snails and slugs

• Examples: Nudibranch - Sea slugs • Mantle secretes hard protective shell.• Some don't have shell.• All terrestrial mollusks are in this

class, but most members are marine.• Terrestrial mollusks don't have gills.

Class Gastropoda - Snails and slugs

• Uses Radula to scrape algae for food

• Foot adapted for locomotion. It forms a slimy path then ungulates foot (wave like motion)

• Eyes are located on a pair of stalk like tentacles on the head

Class Bivalvia - Clams, oysters and scallops

• Examples - Oysters, Scallops, Clams,

• Name means: bi - "two", valva - "part of a door"

• Edge of Mantle secretes a two part hinged shell. Composed of Calcium Carbonate. Shell shows growth lines.

• No distinct head region, but have a central ganglia above foot

• Most are Sedendary/Infaunal, exception scallops and shipworms. Most are Filter feeders

Class Bivalvia

• Nervous System- touch and photoreceptors

• Muscular System • Adductor muscles connect the two valves

together.• Muscular foot used to dig into the sand

and locomotion• Nutrition - Filter feeders. • Use a hollow tube called a siphon to pull

in water. Water is then drawn over the gills then out the excurrent siphon.

Class Bivalvia

• Reproduction • Sexual, Most species have separate

sexes, few hermaphrodites. Shed sperm and eggs into water. Fertilization is external.

• Zygote develops into a free swimming trochophore larva.

• Teredo (Shipworm) - feeds on cellulose that it ingests

The Atlantic Shipworm (Teredo navalis), introduced in 1913, resulted in $3.1 billion (in today's dollars) in damage

to wooden structures on the Bay between 1919 and 1921.

Class Polyplacophora - chitons

• Shell is embedded in mantle• Mantle cavity has two lateral

grooves on each side of body where gills are located.

• Use Radula to scrap algae• Reproduce externally, Separate

sexes

Cephalopods(head feet)Invertebrate Video Clip

Cephalopods History

• appeared some time in the late Cambrian several million years before the first primitive fish began swimming in the ocean

• Scientists believe that the ancestors of modern cephalopods (Subclass Coleoidea: octopus, squid, and cuttlefish) diverged from the primitive externally shelled Nautiloidea (Nautilus) very early - perhaps in the Ordovician, some 438 million years ago.

Cephalopod Hist. cont

• Cephalopods were once one of the dominant life forms in the world's oceans

• Today there are only 650 or so living species of cephalopods (compare that with 30,000 living species of bony fish). However, in terms of productivity, some scientists believe that cephalopods are still giving fish a run for their money

Cuttle fish Sepioloidea lineolata

Squid Taningia danae

Octopus Hapalochlaena lunulata

Cephalopods

• Fast swimming predatory animals• Extremely intelligent• Cephalopods foot is divided into

tentacles– squid=10 tentacle– octopus=8 tentacle– cuttle fish=6 or more tentacle

Cephalopods distinct structures

• Cephalopods have large, well developed eyes that form images

• Tentacles are covered with suckers for seizing and holding prey

• Cephalopods have a rasp like structure in their digestive tract called a radula for breaking down food

• Cephalopods mouth has two strong beaks for tearing its prey apart.

• Cephalopod is fitted with a funnel like structure that fills with water and ejects it acting like a jet propolsion

Cephalopods masters of deception

• Able to change multi colors• Can expand and contract pigment cells in

its skin• Chromatophores(color cells) give the

cephalopod the ability to change. • Can eject ink when alarmed causing the

enemy to be temporarily blinded. The ink also inactivates predators chemical receptors used for detecting prey.

Cephalopods Diet

• Feed on crabs, shrimp, fish, and other cephalopods

Cephalopods Habitat

• Intertidal to abyss• Polar to tropics• In other words they are found

everywhere

The Infamous Giant SquidArchiteuthis

Giant Squid – VideoSperm Whale Clip

• Giant squid get up to 60 feet (20 m) in length and easily hold the record as the worlds largest invertebrate

• Despite the size of these beasts no one has ever seen one alive in its natural environment or have they???

• Main Diet of the sperm whale• Giant squid were once mistaken for sea

monsters in sailing days