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TAMU MARB 435 - Mollusk part 2 gastropods
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MARB 435 1st Edition Lecture 11 Current Lecture: Mollusks part 2Class Gastropoda Contains over ½ of all living mollusc species Inhabit marine, freshwater and terrestrial environments Large diversity of lifestyles and habitatsGastropods undergo torsion, which is a 180° twist of the visceral mass, shell and mantle cavity relative to the foot and head during early development Why does this happen?Benefits:- Head can withdraw into shell first- Ventilation of gills- Tasting of water with osphradium- Better hydrodynamicsDrawbacks:- Fouling waste from anus and excretory pore falls on the headGastropods can be herbivores, carnivores, suspension feeders, and also parasites.Excretion:- Marine gastropods are usually ammonotelic (i.e. produce ammonia as end products of protein metabolism)- Terrestrial gastropods are ureotelic or uricotellic (i.e. produce urea or uric acid as end products of protein metabolism)- Freshwater and amphibious species may be either ammonotelic or ureotelicThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Intertidal species may switch between both modes depending on tidesGastropod larva:Trichophore stage is often skippedVeliger larva is more commonHowever, many are direct developersGastropod Systematics: Has changed dramatically over the last decades Traditionally three subclasses prosobranchia opisthobranchia pulmonata None of the subclasses is supported by phylogenetic analysis No consensus yet on new classification Use names informally: prosobranchs, opisthobranchs, pulmonatesProsobranchs: Mostly marine Gonochoric Mantle cavity anterior Generally solid shell Often operculumCone Snails More than 500 extant and several hundred extinct species in the hyperdiverse genus Conus Morphologically relatively uniform but very diverse in feeding ecology Prey types: Worms, mainly annelids Other gastropods Fishes Most species are very specialized in their diet Conotoxins: Mix of neurotoxic peptides, highly variable even within species Can lead to a variety of neurological symptoms in humans, sometimes to death Mainly used for prey capture Injected into the prey through a hollow radula tooth Toxins work by blocking receptors and ion channels (e.g. sodium, potassium, calcium) Some prey become immune by changing the structure of the receptor or channel proteins Evolutionary arms race between predator and preyEuthyneura: Opisthobranchs and pulmonates Hermaphrodites Characterized by Detorsion: Torsion is partially reversed by about 90° Mantle cavity is on the right side of the body (or is absent) Visceral nerve cords no longer crossed overOpisthobranchs: Marine Shell reduced or lost No operculum Hermaphrodites Detorsion Secondary bilateral symmetryNudibranchia:• Shell, mantle cavity and sometimes gills absent• Body secondarily bilaterally symmetrical• Anus posteriorPulmonates: Terrestrial or freshwater Loss of ctenidia Tendency for detorsion Mantle cavity on the right Hermaphrodites Loss of shell


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