Unit 3.9 Mollusks Marine Science
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Marine Science Unit 3.9 Mollusks Entry Task(s) What do you know about the following organisms? Mollusks Unit 3.9 Mollusks Vocabulary. • Using Chapter 9 (pgs. 218-234) of the textbook provide a definition for each term. • Be sure to complete the vocabulary as we progress through the unit, it will be checked prior to the assessment. Note: The “Unit 3.9 Mollusks Vocabulary” worksheet can be located on the Marine Science webpage @ link: https://www.steilacoom.k12.wa.us/Page/6827 Entry Task(s) Why is one group of mollusks called bivalves? • They have two shells that are hinged together. What kind of symmetry do mollusks have? What does this kind of symmetry mean? • Bilateral Symmetry • When viewed down the center the left & right sides of the organism will be nearly identical. Graphic Organizer Bivalves & Gastropods GO Instructions: • Read through the introduction to the graphic organizer. • Using pgs. 219-223 of the textbook, fill in the Bivalve half of the graphic organizer. • Be detailed in your information. Note: The “Bivalves & Gastropods GO” graphic organizer can be located on the Marine Science webpage @ link: https://www.steilacoom.k12.wa.us/Page/6828 Entry Task(s) What are some of the basic structures of mollusks? • Soft. • Bilateral symmetry. • Bodies contain head, foot, & coiled visceral mass. • Most have either an external or internal shell. What allows a bivalve to control the opening & closing of its shell? • Adductor Muscle Mollusks Mollusks Animals that inhabit shells • Protection for their soft bodies. • Not all mollusks have shells - Squid & octopus have soft bodies, as well as structural & developmental characteristics of shelled mollusks. Pg. 219 Mollusks Mollusks Phylum Mollusca • 100,000 species classified into several distinct classes. • Soft, bilaterally symmetrical bodies composed of a head, foot, & coiled visceral mass (internal organs). • Most have either external or internal shell. • Advanced features of coelom & brain. Entry Task(s) What can the bands of a clam tell us? • The age of the clam. How is the above possible? What does the width of the bands tell us? • Each band of the clam represent about a years worth of growth. • Wider bands represent favorable years of growth. Mollusks What do these organisms have in common? • Two shells making them bivalves (“two shells”) Pg. 219 Mollusks Structure of a Typical Bivalve The two shells are hinged. • Kept closed by a short, tough adductor muscle. - Clams, oysters, & mussels have two - Scallops have one Mollusks Structure of a Typical Bivalve The clam (Mercenaria) is a common bivalve. • 15,000 species of clams. • Live buried in the sand. Mollusks Structure of a Typical Bivalve The age of a bivalve can often be determined by its shell. • Each line (or band) is a new layer of shell the clam has • produced in about a year. • Some bands are wider than others. - More growth during years with favorable conditions. • Oldest living clam = 60 years Pg. 220 Mollusks Structure of a Typical Bivalve Mollusk shells are made of calcium carbonate (CaCO3) • A thin membrane (mantle) line the inside & protects internal lineorgans. organs. - Contains shell glands that secrete calcium carbonate. Pg. 242 Mollusks Structure of a Typical Bivalve Pg. 242 Mollusks Life Activities of Bivalves Bivalves feedconduct & conduct gas exchange gas exchange & feed through a siphon protruding between the shells. • Incurrent siphon - water containing food & oxygen enters. • Excurrent siphon - Waste products of digestion & respiration are eliminated. Mollusks Structure of a Typical Bivalve Breathe using gill membranes. • Surface of gills contain cilia, creating a current. • Water moves over gill surfaces & dissolved oxygen diffuses through gill membrane. • Carbon dioxide diffuses back into the water. Mollusks Life Activities of Bivalves Filter feeders. • Single bivalve can filter up to five liters of water an hour. • Plankton & organic debris enters. • Food particles get stuck in mucus that coats gills & mantle. • Ciliated cells moves food to the mouth (opposite siphon). • Food digested in a one-way digestive tract. • Open circulatory system in which nutrients & oxygen are transported via colorless blood. Mollusks StructureLife Activities of a ofTypical Bivalves Bivalve Adaptations that secure bivalves to substrates. • Mussels live in turbulent waters with constant wave action. - Tough byssal threads made of a fibrous protein. - Secreted from gland in the foot. - Firmly attach them to hard substrates. Pg. 222 Mollusks StructureLife Activities of a ofTypical Bivalves Bivalve Adaptations that secure bivalves to substrates. • MusselsOysters havelive in a turbulentflat upper waters shell that fits the curved lower shell. - Lower shell secretes a cement that adheres to substrates. - Dental scientists interested in chemical properties for dental fillings. Pg. 219 Mollusks Life Activities of BivalvesStructure of a Typical Bivalve Adaptations that secure Adaptationsbivalves to substrates. that secure bivalves to • Under the proper conditions,• Under oysters the proper & other conditions, bivalves oysterscan produce natural pearls. & other bivalves can produce natural - Develops when a grain of sand or other particles lodges between the mantle & the shell. - Mantle tissue reacts by secreting layers of shell around the foreign body, forming a pearl. Mollusks Movement in Bivalve Not all bivalves adhere to substrates; some bivalves move. Variety of adaptations for locomotion. • Scallop is the fastest of the bivalves. - Quick movements occur when adductor muscle contracts & relaxes repeatedly. - Water is forced between the shells propelling the scallop. Mollusks Movement in Bivalve Variety of adaptations for locomotion. • Other bivalves move rapidly through substrates. - Razor clam (Ensis directus) & soft-shell clam (Mya arenaria) use their muscular foot for digging. - Burrowing quickly enables the clam to escape enemies. Pg. 223 Mollusks Movement in Bivalve Variety of adaptations for locomotion. • Some clams, shipworms (Teredo), even burrow through solid substrates, such as wood. Pg. 223 Entry Task(s) From what are byssal threads secreted? • Glands in the foot. From where is the cement of oysters secreted? • Mantle of the lower shell. Mollusks Reproduction in Bivalve Separate sexes. • Fertilization & development are external. - Eggs & sperm are released into the water where fertilization occurs. - Early stages of development, bivalves are part of the plankton population. - When shells form, they sink to the seafloor, settle, & mature into adults. Mollusks Complete the following pertaining to bivalves. • Read pgs. 218-223 in the textbook. • Complete the following review within your science notebook: 1) How does a bivalve breathe? 2) Explain how a bivalve feeds. 3) Compare locomotion in the clam & the scallop. Assessment MSS8-3.9 Mollusks Assessment_01 • Grab a copy of the assessment. • Only using your knowledge of what you have learned complete the assessment. • Once complete, raise your hand so I can collect your paper. Mollusks How Do Gastropods Carry Out Their Life Functions? What do these organisms have in common? Mollusks How Do Gastropods Carry Out Their Life Functions? Gastropods are a diverse group. • About two thirds of the mollusk population. • Referred to as univalves (“one shell”) • In the class of Gastropoda (“stomach-foot”) Mollusks Structures of a Typical Gastropod. Snails, the most common gastropods, have a single coiled shell. Pg. 225 Mollusks Structures of a Typical Gastropod. Glide across substrates on a large muscular foot. Contain a one-way digestive tract. • Ingested through the mouth; waste eliminated through the anus. • Nutrients transported in an open circulatory system. - One-chambered heart & tiny blood vessels. - Colorless blood pushed by contractions of the heart & body muscles. Mollusks Structures of a Typical Gastropod. When not feeding or moving about, a snail retracts its soft body inside its shell. • Opening covered by operculum, like a trapdoor. - Composed of a protein. Pg. 224 Mollusks Life Activities of Snails. Respiration. • Takes in oxygenated water through siphon. • Gills conduct gas exchange. Movement. • Carried out by the nervous & muscular system working together. • Impulses in brain reach foot muscles by motor nerves. • Have ability to crawl & climb. Mollusks Life Activities of Snails. Feeding. • Move along the seafloor grazing on tiny organisms. • All gastropods have a toothed structure (radula), used to scrape & ingest algae. • Periwinkle (Littorina) - Grazes on algae growing on rocks & marsh plants. Mollusks Life Activities of Snails. Feeding. • Mud snail (Ilynassa) - Scavenger feeding on dead, or dying organisms. - Use radula to tear & shred dead matter into small pieces. Mollusks Life Activities of Snails. Feeding. • Moon snail (Neverita) - Predator that secretes chemicals from gland in foot that softens clam shells. - Radula drills small hole into hinged area of clamshell. - Inserts mouth into hole & feeds on the soft-bodied animal inside. Pg. 226 Mollusks Life Activities of Snails. Feeding. • Cone snail (Conus) - About 500 species - Predatory snail, that uses toxins to kill prey. - Harpoon like radula at the end of proboscis used to spear prey. - Toxin being studied on vertebrate nervous systems as treatment for pain relief. Pg. 226 Mollusks Reproduction in Snails. Some species have separate sexes, while others are hermaphrodites. • Internal fertilization & external development. • Some deposit fertilized eggs directly into the water, other enclose eggs