How does Mollusca fit in Mollusca Arthropoda Nematoda Rotifera Annelida Platyhelminthes Porifera Nemertea Cnidaria unknown common ancestor Phylum Mollusca soft bodied animals Mollusca Characteristics Triploblastic Organ level of organization Bilateral Symmetry Cephalization Eucoelomate Protostome Mollusca Characteristics Gas Exchange mainly gills however terrestrial species have evolved lungs Circulatory System open circulatory system in most classes heart and blood sinuses Excretion most have kidneys metanephridia Nervous system ventral nerve cords sensory organs Mollusca Characteristics Digestive System complete with regional specialization Radula a tongue like organ bearing rows of teeth that is used in feeding scraping drilling etc hole made by a moon snail radula 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 a veliger larva trochophore veliger Mollusca Characteristics Body Plan head foot contains sensory organs and muscles visceral mass contains digestive reproductive circulatory organs mantle secretes the shell if there is one cavity contains gills or lungs shell Visceral mass foot mantle mantle cavity 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 There are approximately 50 000 living species in phylum Mollusca 35 000 are extinct The great morphological diversity is the result of elaboration on the basic body plan HAM 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 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 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 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 reduced internal shell shell called a cuttlefish bone Class Cephalopoda Octopus have lost the shell completely most intelligent invertebrate Class Cephalopoda Reproduction male transfers a spermatophore to female using a special pair of tentacles female seals herself up in a den to lay eggs which she attaches to the top of the den she cares for these eggs in some species up to 6 5months after the eggs hatch she usually dies Class Cephalopoda the largest giant squid found to date have been 18 meters in length they live in the deep sea sperm whales 20m in length are their major predators Class Polyplacophora the chitons Class Polyplacophora have 8 rows of articulating plates use radula to graze algae on substrate mantle forms a girdle around plate edge no veliger larvae girdle plates Class Scaphopoda the tusk shells Class Scaphopoda shell is modified into hollow tube that is open at both ends the mantle wraps completely around the visceral mass sessile and feed in sediment located above sand located below sand feeding tentacles Ecology Molluscs have many different means of defense ink cloud as a distraction ink cloud as a dummy deadly venom and warning coloration Ecology Molluscs have many different means of defense many nudibranchs that feed on cnidarians collect and store the undischarged nematocysts in cnidosacs they then can use these nemtocysts for their own protection How does Mollusca fit in Cephalopoda Gastropoda Polyplacophora Nematoda Rotifera Arthropoda Annelida Platyhelminthes Porifera Nemertea Cnidaria unknown common ancestor Scaphopoda Bivalvia Websites Sea slugs and sea hares www seaslugforum net
View Full Document
Unlocking...