MARB 435 Lecture 12 Outline of Last Lecture 1 Introduction to Phylum Nemertea 2 Proboscis 3 Lifestyle of Nemertea 4 Introduction to Mollusca 5 Mollusca Synapomorphies 6 General Morphology 7 Ctenidia 8 Body Cavity and Circulation 9 Development 10 Coelom Formation 11 Trochophore Larva 12 Class Polyplacophora 13 Class Aplacophora 14 Development in Epimenia babai 15 Class Monoplacophora 16 Class Scaphopoda Outline of Current Lecture 1 Class Gastropoda 2 Torsion 3 Feeding Modes 4 Excretion 5 Larval Development 6 Gastropod Systematics 7 Prosobranchs 8 Cone Snails 9 Conotoxins 10 New Zealand Mud Snail 11 Channeled Apple Snail 12 Euthyneura 13 Opisthobranchs 14 Sea Hares 15 Nudibranchia 16 Pulmonates Current Lecture Class Gatropoda This 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 Torsion Torision 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 Modes There 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 organelles to 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 residing inside a host They usually have a negative effect on the host An example of a parasite is Boonea sp which is a gastropod that lives in the coelomic cavity of sea cucumbers Excretion Marine gastropods are usually ammonetelic which means they produce ammonia as end products 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 Development Gastropods often skip the trochophore stage ad the veliger larval is more common There are many direct developers Gastropod Systemmatics Gastropod 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 Proscobranchs The characteristics for these species are listed below Marine species Gonochoric Mantle cavity located in the anterior Solid shell present Operculum structure Proscobranch species are Oyster drills Stramonita haemastoma Moon snail Polinices sp Periwinkle Littorina sp Lightining Whelk Busycon contrarium Marsh periwinkle Littorina irrorata Cone Snails There 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 Conotoxins Conotoxins 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 death occurs 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 Snail The 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 Snail The 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 Euthyneura These 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 Opisthobranchs There qualifications are listed below Marine species Shell is reduced or lost No operculum Hermaphroites Detorsion occurs Secondary bilateral symmetry Sea Hares The 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 and are an important model system for neurobiology They have simple nervous system with large ganglia Nudibranches The organisms