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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