Mollusks and Echinoderms

What is a mollusk?

Mollusks are invertebrates with soft bodies that are often protected by a hard shell (oysters, clams, snails).Some lack the shellAll mollusks have a thin layer of tissue that covers their internal organs called the mantle.Found everywhere.

Other Structure

Mollusks have bilateral symmetry.Internal organs include kidneys: What are they used for?Many mollusks also have a structure called the radula: a flexible ribbon of teeth. This structure is used to scrape food off of objects.

Snail radula

History

Mollusks have been around for millions of years.We know this because their hard shells form very nice fossils.Also form Limestone.What are fossils?

Limestone

Biological sedimentary rock—formed from shells of organisms (mollusks) over many years.Different names of limestone based on how rock is formed, its appearance or composition.Limestone is rock by definition that contains at least 50% calcium carbonate.

Types of Limestone

Coquina: A poorly-cemented limestone that is composed mainly of broken shell debris. It often forms on beaches where wave action segregates shell fragments of similar

size.

Other types of limestone

Chalk: A soft limestone with a very fine texture that is usually white or light gray in color. It is formed mainly from the calcareous shell

remains of microscopic marine organisms such as foraminifers or the calcareous remains from numerous types of marine algae.

Limestone rock

Tufa: A limestone produced by precipitation of calcium-laden waters at a hot spring, lake shore or other location.

Coral reef forming limestone from calcium carbonate skeletons

Limestone- Forming Environment

Nasa satellite image 100mi wide

Stomach Foot

The largest group of mollusks are the snails and their relatives (gastropods).Get their name from the fact their stomach and foot are in the same area.

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Live everywhere from the ocean to treetops.Can be herbivores, scavengers and carnivores (cone shell).Many snails have a tight fitting trap door on their shell that they can close off if threatened.Slugs have the same features as snails except one.

Gastropods

Snails

Slugs

Two Shelled Mollusks

Have two shells held together by a hinge and muscle.Lack radulaAre filter feeders - use their gills to catch food as they breathe.Food sticks to mucus on the gills; then cilia take it to the stomach.

Bivalves

Bivalves have three layers in their shell. The inside layer has a pearly appearance.As adults typically stay in one place.Clams and scallops however can actively move if startled– Clams use their foot if startled to bury themselves.– Scallops can clap their shells to leap away.

Bivalves

Sea Scallop Giant Clam

Anatomy of an Oyster

Clams

                                          Asian Clam

                             

Greater European Peaclam

Mussels

                    

                                      

How are Pearls Formed?

Pearls are formed when a sand grain or parasitic worm gets caught in a bivalve. The mantle becomes irritated and produces the pearly layer over the irritation. This just makes it bigger and more irritating. It keeps putting on layer after layer forming a pearl.

Pearls

Cultured pearls are formed when the shells are opened and different shape beads areinserted.

Natural pearls vary in size and shape. Their shape depends on the piece being coated. These are rare and very expensive.

Natural Black Pearl

Formation of a Pearl

                                                       

           

Head Foots

Cephalopods means “head-footed”. Foot is adapted as tentacles around the mouth.Some members of this group are the octopus, cuttlefish, and squid.Most advanced of all invertebrates.

Octopus

Found only in the ocean where they move by jet propulsion.Communicate by changing the color and patterns of their skin.Use their tentacles and suckers to capture food.Excellent vision and nervous system.They have even been found to remember things they have learned in captivity.

Blue-ringed octopus. One of the most toxic animals.

Why does this use a bright coloring?

Squid

Giant Pacific Squid

                                  

                                                                                                                                                                              

                      

Cuttlefish

                                                                                            

http://www.uwlax.edu/biology/Zoo-Lab/Lab-06/Index-Lab-6.htm

The Echinoderms

Spiny Skinned animals

Have radial symmetry (?)Invertebrates that live in the ocean.Have an endoskeleton that is made up of calcium plates: Where would we find an endoskeleton?Symmetry is based on fivesAlso have a water vascular system

Sea Stars or Starfish

Dissected starfish. Notice the radial canals which are part of the water-vascular system.

Brittle Star

Sea Lily

Sea Lily or Feather star

                                          

                    

Sea Urchin

Sand dollar

Sand dollars

Arrowhead

Flat Round

Sea Biscut

Pancake

Sea Gopher

Sea Cucumber

Water vascular system

Parts of the tubes can contract and squeeze the water into tube feet. This allows the feet to grip the surface underneath the organism, allowing it to move.They also use these tube feet to pull open the shells of mollusks

Water-Vascular System

Tube feet

Sea Star

When feeding, a sea star grasps a bivalve (?) with all of its feet and pulls the shell open.Once the shell is open the sea star forces its stomach out of its body and into the clam, and digests it externally.What other two organisms have we seen do this?Can regenerate lost arms. Some species lost arms can grow new bodies!!

Other Echinoderms

Brittle stars are close relatives to sea stars. Except their arms are extremely long, slender, and flexible.Sea urchins and sand dollars lack arms, but have hard spines. These spines are mobile and are used for movement.Have teeth that they use to scrape food off of objects.

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Sea cucumber bodies are soft and flexible.Some have tube feet on their underbelly for which they use to move across the sea floor.They crawl along the sea floor sucking in food found in the sand.Other sea cucumbers are filter feeders that use their tube feet to catch food particles in the water.

Review

What type of symmetry do mollusks and echinoderms have?Who are the three groups of mollusks?What is a radula?What organ system do they have that the worms lacked?What happens if you cut an arm off of a star fish?How does the water vascular system work?