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 shell All 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.

Continue 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 radula Are 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                                                                          Greater European Peaclam Asian Clam

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 Natural pearls vary in size and shape. Their shape depends on the piece being coated. These are rare and very expensive. Cultured pearls are formed when the shells are opened and different shape beads are inserted.

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.

Why does this use a bright coloring? Blue-ringed octopus. One of the most toxic animals.

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 fives Also 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.

Continued 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?