pseudocoelomates acoelomate em at o da el m in th es ot ife ra An ne lid a M ol lu sc a Ar th ro po da Ec hi no de rm at a Ch or da ta R N Pl at yh protostomes eucoelomates Phylum Mollusca soft bodied animals Mollusca Characteristics Body Plan head foot contains sensory organs and muscles visceral mass contains digestive reproductive circulatory organs mantle skin of the dorsal body wall secretes the shell if there is one cavity contains gills or lungs shell Visceral mass foot mantle mantle cavity periostracum conchiolin prismatic layer calcium carbonate nacreous layer calcium carbonate and proteins mantle HAM Hypothetical Ancestral Mollusc gonads Mantle coelom Shell Nephridium hear t Anus Digestive gland head Gill Mouth Radula foot Nerve collar Nerve cords Intestine Mollusca Characteristics Feeding and Digestion There are both free living and parasitic forms Most species use a tongue like organ called a radula when feeding radula retractor radula esophagus odontophore retractor radula protractor odontophore protractor odontophore Mollusca Characteristics Feeding and Digestion Mollusca Characteristics Digestive System complete with regional specialization digestive gland anus stomach intestine Mollusca Characteristics Gas Exchange mainly gills however terrestrial species have evolved lungs axis afferent blood vessel into gill water efferent blood vessel out of gill Mollusca Characteristics Gas Exchange gill gill foot gill foot Mollusca Characteristics Circulatory System open circulatory system in most classes heart and blood sinuses heart coelom Mollusca Characteristics Excretion most have kidneys metanephridia tubules connecting pericardial cavity coelom and nephridiopore nephridiopore Mollusca Characteristics Nervous system nerve ring pedal nerve cord visceral nerve cord Mollusca Characteristics Reproduction monoecious and dioecious species exist usually internal fertilization indirect development with the presence of a trochophore larva link to annelids and in most cases also a veliger larva trochophore veliger ovisacs Lampsilis ovata The juvenile stages of some bivalves are parasitic Glochidia larval bivalves that are parasitic on fish gills ovisacs Lampsilis ovata Some freshwater bivalves have evolved ways of attracting hosts for their larvae Some species place their larva in a lure called a superconglutinate http courses smsu edu mcb095f gallery L perovalis lampsilis perovalis htm Molluscan Radiation There are approximately 128 000 living species in phylum Mollusca 35 000 are extinct The great morphological diversity is the result of elaboration on the basic body plan HAM HAM Hypothetical Ancestral Mollusc gonads Mantle coelom Shell Nephridium hear t Anus Digestive gland head Gill Mouth Radula foot Nerve collar Nerve cords Intestine Molluscan Radiation Gastropoda torsion coiling of the shell Scaphopoda ventral shell fusion Polyplacophora shell consists of 8 plates HAM Cephalopoda Bivalvia bivalved shell dorsal hinge lobed foot highly developed head shell reduced or lost Phylum Mollusca Class Gastropoda Class Bivalvia Class Cephalopoda Class Polyplacophora Class Scaphopoda Class Gastropoda snails and slugs Torsion twisting of the visceral mass through a 180 rotation 1st 90 rotation usually occurs at the veliger stage the 2nd 90 rotation usually takes longer and occurs later after torsion the anus and mantle cavity end up over the head this poses a serious fouling problem and many gastropods have lost their right gills kidneys and heart auricles mouth mouth anus gills gills anus anus gills Larval torsion anus mouth Coiling Planospiral shell Apex of shell extends out making the shell more compact Conispiral shell Shell shifts over body for better weight distribution Class Gastropoda Subclass Prosobranchia Subclass Opisthobranchia Subclass Pulmonata Class Gastropoda Subclass Prosobranchia aquatic snails marine and freshwater have undergone torsion and most have undergone shell coiling have gills all have shells use radula for feeding can be herbivores carnivores or detritivores In some mantle extends over shell Class Gastropoda Subclass Prosobranchia snails often lay eggs in protective capsules Class Gastropoda Subclass Opisthobranchia sea hares and sea slugs nudibranchs have undergone detorsion have gills sea hares have a reduced shell sea slugs have no shell Detorsion mouth anus gills They are missing the right gill kidney and heart auricle Class Gastropoda Subclass Opisthobranchia sea hares and sea slugs nudibranchs Class Gastropoda Subclass Opisthobranchia they usually crawl along the bottom but many can also swim by using their modified mantle as wings Class Gastropoda Subclass Opisthobranchia all are monoecious sea hares often form mating chains acts as male only act as both males and females simultaneously acts as female only Class Gastropoda Subclass Opisthobranchia sea slugs often lay ribbons of eggs which stick to the substrate Class Gastropoda Subclass Pulmonata land snails and land slugs have lungs land slugs have undergone detorsion and have lost their shell Class Bivalvia class Pelecypoda the bivalves Class Bivalvia clams mussels oysters scallops use gills for respiration and filter feeding shell is modified into a bivalved shell connected by muscles and ligaments no head reduced sensory organs no radula foot can be modified for digging dorsal umbo the oldest part of the shell anterior posterior ridges show where mantle has laid down shell ventral siphons foot labial palps gills excurrent siphon Incurrent siphon mouth foot anus intestine Zebra Mussels Dreissena polymorpha Native to Asia introduced to the North America in ballast water Consequences of zebra mussel invasion 1 2 3 4 Decrease in phytopalnkton increase in water clarity Change lake food webs Out compete native mussels Cause physical damage to water intake pipes Richard E Young Michael Vecchione and Katharina M Mangold Class Cephalopoda the squids octopus nautilus and cuttlefish Class Cephalopoda shell is present reduced or lost all are predacious with beak like jaws highly developed head and sensory organs very intelligent closed circulatory system swim via jet propulsion foot is lobed and forms tentacles direct development no larvae Class Cephalopoda Nautilus have a chambered shell that aids in maintaining buoyancy chambers are filled with gas chambers siphuncle cord of tissue connected to visceral mass Class Cephalopoda Squids have a reduced internal shell shell called the pen Cuttlefish have a
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