MARB 435 Lecture 12 Outline of Last Lecture1. Introduction to Phylum Nemertea2. Proboscis3. Lifestyle of Nemertea4. Introduction to Mollusca5. Mollusca Synapomorphies6. General Morphology7. Ctenidia8. Body Cavity and Circulation9. Development10. Coelom Formation11. Trochophore Larva12. Class Polyplacophora13. Class Aplacophora14. Development in Epimenia babai15. Class Monoplacophora16. Class ScaphopodaOutline of Current 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. PulmonatesCurrent LectureClass GatropodaThis class contains over hald of all living mollusk species .They’re marine, freshwaters and terrestrial species. They contain a large amount of diversity not only in species but also in habitats and lifestyles. Gastropods are commonly defined as having a one-piece shell and muscular foot. They undergo cephalization and have stalk bearing eyes on their heads.TorsionTorision is the 180 ° twist of the visceral mass, shell, and mantle cavity relative to the foot and head during early development. The benefits of torsion is the head withdraws into the shell first, ventilation of gills occur, tasting of water with osphradium is common, and better hydrodynamics. The drawbacks are fouling which is the wastefrom the anus and excretory pore falls on their heads.Feeding ModesThere are four main feeding modes for gastropods, being herbivores, carnivores, suspension feeders or parasites.- Herbivores- Eat plant particles or plant components. Littorina sp. (periwinkles) are browers that feed on microalgae in the rocky intertidal region of water. Elysiz viridis pierces algal cells and suck out their cytoplasm. The radula has only a single tooth for each row which is how the organism pierces the algal cells. Terrestrial herbivores produce cellulose to digest the plant material they consume.- Carnivores- These species eat other organisms for energy. The Giant Triton paralyzes its prey using the sulfuric acid produced in their salivary glands. The Giant Triton is parasitic to the Crown of Thorns in the Pacific Oceans. The Oyster Drill uses a combination of mechanical abrasion techniques and chemical breakdown methods to peirce through oyster shells. Nudibranchs (sea slugs) are a type of carnivore that feed on sessile organisms like cnidarians and sponges. The carnivore is usually has specialized organellesto capture their desired prey.- Suspension Feeders- These are animals that feed on materials suspended in the water column such as plankton. Sponges are an excellent example of suspension feeders that feed on plankton and they’re excellent suspension feeders. Worm snails are another type of suspension feeder that stick out their gills to catch particles in the water.- Parasitic- These are organisms that receive their support, food and habitation by residinginside a host. They usually have a negative effect on the host. An example of a parasite isBoonea sp. which is a gastropod that lives in the coelomic cavity of sea cucumbers.ExcretionMarine gastropods are usually ammonetelic which means they produce ammonia as endproducts of protein metabolism. Terrestrial gastropods are ureotelic and uricotellic and they produceurea and uric acid as an end product of protein metabolism. Freshwater and amphibious species may be either ammonotelic or ureotelic. Intertideal species my switch between both modes depending on the tides.Larval DevelopmentGastropods often skip the trochophore stage ad the veliger larval is more common. There are many direct developers.Gastropod SystemmaticsGastropod systemmatics have changes so much over the last decades. There are three subclasses when discussing gastropod systemmatics, proscobranchia, opisthobranchis and pulmonates. Pulmonates and opisthobranchia are commonly grouped together Euthyneura. None of the subclasses are suppoted by phylogenetic analysis.ProscobranchsThe characteristics for these species are listed below.- Marine species- Gonochoric- Mantle cavity located in the anterior- Solid shell present- Operculum structureProscobranch species are Oyster drills Stramonita haemastoma, Moon snail Polinices sp., Periwinkle Littorina sp., Lightining Whelk Busycon contrarium, Marsh periwinkle Littorina irrorata.Cone SnailsThere are more than 500 species extant and extinct species in the hyperdiverse genus. Morphologically relatively uniform but a very diverse in feeding ecology. The prey of cone snails are worms (mainly annelids), other gastropods, and fishes. Most species are very specialized in their diet.ConotoxinsConotoxins are a mix of neurotoxic peptides and highly variable even within species. Conotoxins can lead to a variety of neurological symptoms in humans and in serious cases deathoccurs. They mainly use the nuerological toxins to capture prey. They inject their prey with a hollow radula tooth. Toxins work by blocking receptors and ion channels like sodium, potassium,and calcium. Some prey become immune by changing the structure of the receptor or channel proteins.New Zealand Mud SnailThe New Zealand Mud Snail is the Potamopyrgus antipodarum is 6mm max and reproduces by parthogenesis. A single individual can give birth to 1220 live offspring every 3 months. They were introduced to Montana, California, Oregon, Utah, Wyoming and Colorado.Channeled Apple SnailThe channeled apple snail is known as Poacea cancaliculata. They are herbivores native to South America and they were introduced to Taiwan for the escargot industry. They’re a major pest in rice paddies all over Asia and they’re tolerant to large ranges of salinity. This species lays resistant eggs above the water line.EuthyneuraThese are opisthobranchs and pulmonates. They’re hermaphrodites characterized by detrusion. Detrusion is when the torsion is partially reversed by about 90°. The mantle cavity is on the right side of the body or is simply absent and the visceral nerve cords no longer cross over.OpisthobranchsThere qualifications are listed below.- Marine species- Shell is reduced or lost- No operculum- Hermaphroites- Detorsion occurs- Secondary bilateral symmetry Sea HaresThe sea hares are called Aplysia spp. And they grow up to two feet long and are 2 kilograms heavy. They eat seaweeds and swim with winglike flaps. They can roduce ink