MARB 435 Lecture 14 Outline of Last Lecture1. Class Gastropoda2. Torsion3. Feeding Modes4. Excretion5. Larval Development6. Gastropod Systematics7. Prosobranchs8. Cone Snails9. Conotoxins10. New Zealand Mud Snail11. Channeled Apple Snail12. Euthyneura13. Opisthobranchs14. Sea Hares15. Nudibranchia16. PulmonatesOutline of Current Lecture1. Class Bivalvia2. Bivalvia Morphology3. Pearls4. Bivalvia Classifications5. Attachment6. Boring Bivalves7. Bacterial symbiosis8. Reproduction and Development of Bivalves9. Dreissena polymorpha Zebra Mussel10. Class Cephalopoda11. External Shell12. Internal Shell13. Feeding14. Gas Exchange and Circulation15. Nervous System and Sensory Organs16. Chromaic Organs17. Reproduction and Development of Cephalopods18. Diversity of CephalopodsCurrent LectureClass BivalviaThis class is composed of about 15,000 extant species. They’re mostly marine species and 10-15% of the species reside in freshwater. The freshwater species are clams, scallops, mussels, and oysters.Bivalvia MorphologyBivalves have 2 shell valves with a hinge and a ligament. They usually have one or two adductor muscles. Their bodies are laterally compressed. Cephalization or the process of forming a head and central nervous system doesn’t occur. There is no raduala and bivalves use their gills for respiration.PearlsPearls grow inside of oysters, scallops and clams and mussels which are the freshwater species of the class Bivalvia. The mantle secretes a material around a foreign object to protect itself from the intruder. Pearls can grow over many years. Pearl oyster farming is probably saved the oysters and the oyster form of trade.Bivalve ClassificationBivalves are broken down to three main groups, Protobranchs, lamellibranch and anomaodesmata. The following classifications of each section is grouped below.Protobranch- Despoit feeders- Ctenidia is used for gas exchange- Palp proboscides are used for food captureLamellibranch- Suspension feeders- Ctenidia used for feeding- Secrete byssus threads for attachmentAnomalodesmata- Mostly carnivorous with ‘septibranch’ ctenidiaAttachment The byssus is a bundle of strong protein threads extendingfrom the base of the foot. Occurs in many epibenthic species on hard substrate. The secreted byssus is connected to eight byssal retractor muscles. The contraction of byssal retractor muscles pulls the animal to the substraturm.Boring BivalvesTwo examples are Teredo navalis and Phola dactylus. Teredo navalis burrows to wood and is commonly known as the ship worm. Phola dactylus (paddock) burrows onto soft rocks like coral rubble.Bacterial SymbiosisSome bivalves live in conditions of low nutrients and low oxygen but of high sulfide levels. The bivalves host symbiotic chemoautotrophic bacteria in their gills that oxidize sulfide toproduce energy for carbon fixation. Bacteria is transmitted vertically through the egg from the mother to the offspring.Reproduction and Development of BivalvesAlmost all bivalves are gonochoric and fertilization almost always is external. The larva is trochophore and Veliger.Dreissena polymorpha Zebra MusselThis is a mussel native to freshwater lakes in southest Russia. They were introduced to western Europe and Scandinavia via canals, starting in the 1800s. They were first detected in theGreat Lakes in 1986 and quickly spread to various waterways. They were probably introduced byballast water which is water where ships majorly travel and have high amounts of gravels. The Zebra Mussel females can poduce up to 400,000 eggs per year. They often outcompete with native freshwater mussels and smother other fauna by over growing. The Zebra Mussels can damada boats, harbors and have invaded water treatment plants. They can block pipers also. The Zebra Mussels cause economic an environmental harm.Class CephalopodaThis is a class in Mollusca where shells don’t have to be present. Cephalopods are divided by septa with chambers connected by a siphuncle. They also have a closed circulatory system with a foot modififed to form arms and siphon. They have a complex brain which is encased in a cranium. The shell is usually internal or simply absent except Nautilus. There size can range from a few centimeters to 20 meters. For example giant squids have arms. The dorso-ventral axis becomes the major body axis.External ShellThe largest body cahmber in Cephalopods is the body chamber. A tube of tissue and calcareous material that connects all the chambers is called the siphuncle. The function of the siphuncle is too pump water out and gas into the chambers of the Cephalopoda and this assists with buoyancy regulation. Internal ShellExamples of internal shells are shown in squid, cuttlefish and Spirula spirula. In squid, the shell is reduced to a chitinous pen. In cuttlefish, the cuttlebone is a honeycomb of small gas-filled spaces. In Spirula spirula is the only extant species with an internal coiled shell. Spirula spirula is a type of cuddle fish.FeedingCephalopods are strictly carnivorous organism and they capture prey with oral appendages arms and tentacles which can be differentiated.Their arms are short and heavy appendages covered with suckers. Tenacles are long and retractile with stickers only on spatulate ends of the tentacle.Gas Exchange and CirculationThe gills are non-cilitaed organelles utilized for gas exchange or respiration. They have a closed vascular system where the blood is contained inside the arteries and veins are connectedby capillary beds. They have one systemic heart and two branchial hearts. The blood vessels are lined by endothelium tissue.Nervous System and Sensory OrgansThe nervous system is centralized and the brain is enclosed in a cartilaginous cranium. They undergo complex Cephalization which results in complex eye lenses being formed. The complex eye lenses are housed inside the cartilaginous capsule are fused to the cranium. The eyes are unusually large.Chromatic OrgansThere are two important types of cells one must understand when studying Cephalopods, chromatophores and photophores. Chromatophores are expendable pigment cells that are surrounded by muscle fibers. Photophores are cells which produce bioluminescence. They are bacterial and are produced by symbiotic bacteria.Reproduction and DevelopmentCephalopods are gonochoric. The males produce spermatophores and direct sperm transfer from male to female occurs with heterocotylus. The fertilization usually happens in the mantle cavity