Echinoderms and Mollusks Invertebrates 2: Porifera, Cnidarians, Echinoderms, and Mollusks.
Mollusks
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Transcript of Mollusks
Mollusks
THE WORD MOLLUSK MEANS “SOFT BODY”
MOLLUSKS ARE SOFT BODIED INVERTEBRATES.
Chapter 27-2
PHYLUM MOLLUSKA
But these are hard shells.!!!!***
Where’s the “beef”???
CHARACTERISTICS OF MOLLUSKS
1. SOFT BODY COVERED BY A FOLD OF TISSUE CALLED A MANTLE
2. HEAD AND A MUSCULAR FOOT FOR MOVEMENT
4 Characteristics of MollusksAll Mollusks have:1. Muscular foot - used for locomotion
2. Mantle – thin, delicate tissue that covers the body of the mollusk, like a cloak
3. Shell – usually CaCO3, and secreted by mantle
4. Visceral mass – just below mantle, containing the internal organs
The 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.
The 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.
Function of the Radula
• A layer of flexible skin, with hundred of sandpapery teeth, used to scrape algae off of rocks
• In 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.
Bivalves 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
Respiration
• Gills are used, and have many capillaries to permit diffusion of O2 into blood stream
• Gills on the Nudibranch are particularly cool
Circulatory System
• Open 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 blood
• This works for clams and snails, but not highly motile octopi or squid, which have Closed Circulatory Systems
Excretion- Waste Management 101
• 2 openings in the digestive tract
• Ammonia wastes from protein digestion can be toxic, and are eliminated via Nephridia, simple tube shaped organs leading out of the body, via the skin.
Reproduction• In 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!
Classifying Mollusks Further
1. Class Gastropoda – stomach foot– Broad muscular foot on stomach side– Snails, Slugs, Nudibranchs– Some shelled, others not
– Snail Shell shows RADIAL TORSION, creating the distinct spiral shape
Two Shelled Mollusks – Class Bivalvia
Oysters, Scallops, Clams, Mussels
Free swimming larvae
Mantle manufactures the shell
Pearls 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
Classifying Mollusks Further
2. Class Cephalopoda – “head foot”– High degree of CEPHALIZATION
– Octopi, Squid, Nautilus, Cuttlefish
– Tentacled and highly motile, with excellent senses, particularly the eyes
– Originated 500 million years ago, in Cambrian Period– No shell, but internal shell is present– Jet propulsion
– Ink defense mechanism, Poisonous radula – ewww!