3CHARACTERISTICS OF MOLLUSKS SOFT BODY COVERED BY A FOLD OF TISSUE CALLED A MANTLEHEAD AND A MUSCULAR FOOT FOR MOVEMENT
44 Characteristics of Mollusks All Mollusks have:Muscular foot - used for locomotionMantle – thin, delicate tissue that covers the body of the mollusk, like a cloakShell – usually CaCO3, and secreted by mantleVisceral mass – just below mantle, containing the internal organs
12The All Important COELOM is alive and well in the Mollusks. Here’s why it’s important…The development of a coelom allows for the formation of more complex tissues and organs.It also allowed for a wide variety of body architectures; which allows for coelomates to grow larger.
13The primary means of locomotion is via a muscular FOOT. Sometimes the foot is modified, but it is always present.Mollusks have a definite “head” region that contains organs for chemo-sensory functions.All mollusks, except bivalves, possess a rasping tongue organ called the RADULA.
14Anatomy of the Rasping Tongue, or Radula of a Snail
15Function of the RadulaA layer of flexible skin, with hundred of sandpapery teeth, used to scrape algae off of rocksIn full-on carnivore mode, the radula acts like a drill to pierce shells. These things even have poison glands to make things nastier Octopi and certain sea slugs do this.
17Bivalves are Usually Filter Feeders Think “Clam” when Bleecker says Bivalve.Come on, say it out loud now Feathery Gills are extended from Sessile, or virtually motionless bivalves to screen the water for microorganisms and algae to munch on
18Bleecker Swam up to one of these in Hanauma Bay, on Oahu (Hawaii, people!)
19RespirationGills are used, and have many capillaries to permit diffusion of O2 into blood streamGills on the Nudibranch are particularly cool
21Circulatory SystemOpen Circulatory System – the blood does not always travel in blood vessels, and often deposits into spaces or sinuses to drain back once organs have been bathed with bloodThis works for clams and snails, but not highly motile octopi or squid, which have Closed Circulatory Systems
22Excretion- Waste Management 101 2 openings in the digestive tractAmmonia wastes from protein digestion can be toxic, and are eliminated via Nephridia, simple tube shaped organs leading out of the body, via the skin.
23ReproductionIn a watery environment, egg and sperm are often released in mass quantities in hopes of fertilization. Larvae then swim to a spot on the bottom and grow into bivalves, etc.In tentacled mollusks, modified tentacles are used in Internal Fertilization.Spontaneous sex changes do occur, if there are not enough members of a given sex. Holy cross dressing Batman!
24Classifying Mollusks Further Class Gastropoda – stomach footBroad muscular foot on stomach sideSnails, Slugs, NudibranchsSome shelled, others notSnail Shell shows RADIAL TORSION, creating the distinct spiral shape
25Two Shelled Mollusks – Class Bivalvia Oysters, Scallops, Clams, MusselsFree swimming larvaeMantle manufactures the shellPearls occur when a sand grain or foreign particle is covered in “mother of pearl”, a material used to keep the inside of the shell smooth
26The Pearl Emerges – Black is Particularly Rare
27Classifying Mollusks Further Class Cephalopoda – “head foot”High degree of CEPHALIZATIONOctopi, Squid, Nautilus, CuttlefishTentacled and highly motile, with excellent senses, particularly the eyesOriginated 500 million years ago, in Cambrian PeriodNo shell, but internal shell is presentJet propulsionInk defense mechanism, Poisonous radula – ewww!