Unit Four: Mollusks

Chromatophores

Color cells found in the Cephalopods' skin - Contract and expand to produce different colors and patterns 1) Color reflects their "mood" - They are used to blend into their surroundings in order to catch prey, or hide from predators

Freshwater Clam External Anatomy

- The Umbo is the raised, "oldest part" of the shell and is used to locate the other surfaces - Bivalves have an incurrent and excurrent siphon to bring in water containing food & O2 and for excess water & wastes to leave - The Excurrent siphon is found closest to the Umbo side - the Dorsal surface

Freshwater Clam Internal Anatomy

- Two Strong adductor muscles help open & close the shells (or valves) and must be cut through to examine the interior of the clam - Mantle - Gills are found inside the mantle cavity. They remove oxygen as water flows over them. - The foot is used for movement - clams can move and burrow on the sea floor!

Mollusks: Class Bivalvia

"Hatchet-footed" (ex. the clam) - Kingdom: Animalia, Phylum: Mollusca, Class: Bivalvia - The Class includes Clams (motile), Oysters (sessile), Scallops (motile), & Mussels (sessile) - Soft-bodied invertebrates - Have a muscular foot that can be extended for movement - Two part, hinged shell (the shells are called "valves") - Have a "one-way digestive tract" or system with a mouth and anus - They are dioecious - No distinct "head region" - Have muscular siphons:these pump and circulate water throughout their bodies - for obtaining oxygen from the water and food! - They Filter Feed on planktonic algae - microscopic plants (This means that they are classified as herbivore consumers) - Mussels can be salt water or freshwater - The Body organs (called the visceral mass) are protected by a soft layer of tissue called the mantle. ~ The mantle also makes (produces) the shell - the shell is made of calcium carbonate. - Most are sessile (attached to rocks)

Mollusks: Class Cephalopoda

"Head footed" (ex. squid, octopus, cuttlefish, Chambered Nautilus) - All Members of this class have tentacles that extend from the head. - With the squid and cuttlefish, the mollusk "shell "remains, but it is internal (It is also called the "pen") - The octopus has lost its shell entirely - know that the octopus is evolutionary younger than the squid. - Siphon is also called the funnel

Mollusks: Class Gastropoda

"Stomach-footed" (ex. the snail)

Water flow in Clams

- Incurrent siphons bring in water with food and oxygen - Water is passed over the gills - oxygen diffuses into the clam and carbon dioxide out. 1) Microscopic Cilia on the gills help to pull in water - It is the labial palps that move and direct food into the small mouth

Mantle

A soft tissue that has two big functions: - It protects the internal organs - it is this tissue that makes (or secretes) the limestone shell when the clam is growing

Jet Propulsion Locomotion in Squid

Alternating contractions of mantle muscles expand the mantle cavity to fill it, then expel the water out at high speed - Valves ensure the water flows in the right direction

Colossal Squid

Biggest squid in the ocean - Largest animal eyes ever studied. ~ It possibly has the largest eyes that have ever existed during the history of the animal kingdom!

Giant Clam: Symbiotic Mutualism

Occurs between the clam and unicellular algae cells - The algae live in the tissue of the clam. They are able to obtain the sunlight needed for photosynthesis because the clam lies with its shells pointing upward. ~ Algae are "harvested" or "eaten" by the clam as supplementary food - The algae are assured of a safe "residence" and a get a continued supply of carbon dioxide - The reason for why the clam is able to grow to such a big size in its habitat (habitat is quite nutrient poor tropical sea water.)

Mollusks

Phylum: Mollusca - Common name: Mollusks or Mollusks - Members of this Phylum include the snail, oyster, slug, clam, squid and octopus. - The habitats that Molluscs live in include: oceans, streams, ponds and even moist soil. - approx 100 000 living species! (This is second only to the phylum Arthropoda in terms of named species!) - Three classes: Bivalvia, Gastropoda, and Cephalopoda