Chapter 27 2 PHYLUM MOLLUSKA Mollusks THE WORD
- Slides: 36
Chapter 27 -2 PHYLUM MOLLUSKA Mollusks THE WORD MOLLUSK MEANS “SOFT BODY” MOLLUSKS ARE SOFT BODIED INVERTEBRATES. But these are hard shells. !!!!*** Where’s the “beef”? ? ?
ANIMAL CLASSIFICATION
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 Mollusks All 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 Ca. CO 3, and secreted by mantle 4. Visceral mass – just below mantle, containing the internal organs
Foot of a Clam
Foot, Shell, Mantle, Visceral Mass are always Present in Mollusks
MOLLUSKS ARE GROUPED INTO 3 CLASSES ACCORDING TO THE TYPE OF FOOT SHELL / NO SHELL KIND OF SHELL
2 CLASSES WITH SHELLS OUTSIDE THE BODY UNIVALVE (ONE SHELLED MOLLUSK) BIVALVE (TWO SHELLED MOLLUSK)
3 RD CLASS HAS NO SHELL • INSIDE • OR • OUT
OCTOPUS
SQUID
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.
Anatomy of the Rasping Tongue, or Radula of a Snail
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 • 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 O 2 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.
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
The Pearl Emerges – Black is Particularly Rare
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!
The Nautilus
Bioluminescence! Complicated Chemical Reactions!
Ecological Role 1. 2. 3. 4. 5. Food source – clams, oysters, squid, octopi Filter feeders remove pollutants Indicators of pollution Ships worn down by bivalves Recyclers of waste or detritus
Videos! Killer octopi? • http: //www. youtube. com/watch? v=L_6 j. Q 6 b -Tqg • http: //www. youtube. com/watch? v=b. Na. Rbh 2 dl 6 I
Video 2: Giant squid • http: //www. youtube. com/watch? v=5 dv 9 Jh Q 0 Msw&feature=related Think of the calamari!
Video 3: snails • Snails…um…doing it: http: //www. youtube. com/watch? v=BLu. H 9 h. AH 1 y A
Video 4: Slugs • Slugs also doing it…(whoaaa this one is weird…) http: //www. youtube. com/watch? v=GSW 9 k WIRCOQ
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