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Mollusca
Billman, Bonin, & Olson
Per. 5
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General Characteristics1)Bilaterally symmetrical. 2)Body has more than two cell layers, tissues and organs. 3)Body without cavity. 4)Body possesses a through gut with mouth and anus. 5)Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. 6)Has a nervous system with a circum-oesophagal ring, ganglia and paired nerve chords. 7)Has an open circulatory system with a heart and an aorta. 8)Has gaseous exchange organs called ctenidial gills. 9)Has a pair of kidneys. 10)Reproduction normally sexual and gonochoristic. 11)Feed a wide range of material. 12)Live in most environments.
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General Characteristics After the Arthropods the Mollusks are the most successful of the
animal phyla in terms of numbers of species. There are about 110,000 species known to science most of which are marine.
They also exhibit an enormous range in size, from species which are almost microscopic to the largest of all invertebrates the giant squid which can weighs 270 kg and measures up to 12 meters long in the body, with tentacles as much as another 50 meters in length.
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Classes of Mollusca
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Amphineura
http://animaldiversity.ummz.umich.edu/site/resources/jack_burch/002.rjb1.jpg/medium.jpg
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Monoplacophora
http://biology.fullerton.edu/biol317/im/s02/bc/lined_chiton.jpg
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Gastropoda
http://www.pdphoto.org/jons/pictures2/snail_2_bg_112302.jpg
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Scaphopoda
http://www.sanibel-international.com/SSpincushionl.jpg
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Bivalvia
http://www.diggerschoice-seafood.com/images/littlenecksweb.jpg
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Cephalopoda
http://chemistry.csudh.edu/faculty/jim/cozaugo4-600/octopus.jpg
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Body Plan
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Body Plan
Head-foot– It is mostly a muscular
organ covered in cilia and
rich in mucous cells – includes a mouth, eyes
and tentacles, the last two may be much reduced or
even absent. – species with shells the
head-foot can be drawn into the shell
Visceral Lump– entirely nonmuscular and
contains the organs of digestion and reproduction
– it includes the gonads, the kidney, the heart and the digestive diverticulum.
The body is divided into two functional regions, the head-foot and the visceral lump.
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Feeding
Digestion can occur in a ciliated tract or intracellularly Pelecypods are mainly filter feeders Cephalopods are active predators Gastropods have a sharp radula for drilling through shells
– some species have a single radula tooth while others may have several hundred thousand. In some the teeth are hollow and poison containing and are used as weapons
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Respiration
Use external gills for respiration Diffusion also occurs through
the moist skin Respiration is through gills
called ctenidia.
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CirculationHave an open circulatory system, meaning blood does not circulate entirely within vessels but is collected from gills, pumped through heart, and released directly into spaces in tissues from which it returns to gills and then to heart.
–Such a blood-filled space is known as a hemocoel ("blood cavity").–hemocoel has largely replaced coelom, which is reduced to a small area around the heart and to the cavities of the organs of reproduction and excretion
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Excretion
Carried out by a pair of nephridiaTubular structures that collect fluids from coelom and exchange salts and other substances with body tissues as the fluid passes along tubules for excretion.Nephridia empty into the mantle cavityExcretion of wastes is through structures called metanephridia and through the body and gill surfaces.
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Response•Cephalization is present
• complexity of the nervous system varies with each species
•Neurons are arranged in a ganglial pattern with two longitudinal nerve chords and a circum-oesophagal ring
• cephalopods have eyes capable of image formation
•Bivalves don’t have eyes, but they have cells that are tactile and photosensitive
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Movement• the head-foot is the muscular organ with cilia and many mucous cells
• Herbivorous forms glide by way of waves from muscular contraction
• Carnivorous forms such as cephalopods use jet propulsion (water sprayed from the mantle cavity by a siphon)
• Sea Hares and Cuttlefish use lateral fins
• Bivalves use the foot to burrow into the sand
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Reproduction• visceral mass contains the organs of reproduction (gonads)
• usually sexual and gonochoristic
• Fertilization is external
• Mostly dioecious but Gastropods are monoecious
• Egg becomes juvenile (cephalopods, snails, and some bivalves) or the egg becomes a trochophora larva (Chitons, monoplacophorans, scaphopods)
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Bibliography "The Molluscs (Phylum Mollusca) ." The Earth Life Web. N.p., n.d.
Web. 15 Apr. 2010. <http://www.earthlife.net/inverts/mollusca.html>.
"The Mollusca." UCMP - University of California Museum of Paleontology. N.p., n.d. Web. 15 Apr. 2010. <http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.
php>. "Phylum Mollusca." Infusion. N.p., n.d. Web. 15 Apr. 2010.
<http://infusion.allconet.org/webquest/PhylumMollusca.html>. “Phylum Mollusca Lecture Outline.” N.p., n.d. Web. 15 Apr. 2010.
<http://www.d.umn.edu/biology/courses/bio3701/Mollusca.htm>.