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General Characteristics
 Coelomates
 Protostomes
 Body cavity called coelom is completely enclosed
within the mesoderm
 Specialized organs Ex. Stomach
 Soft bodies
 Toothed tongue called radula composed of chitin
 Three distinct body zones
 Head-foot
 Visceral mass
 Mantle
Classes Within Mollusca
Bivalvia
 Ex. Clam
Monoplacophora
 Ex. Neopilina
http://www.manandmollusc.net/Shell_photos/monoplacophora.gif
http://cas.bellarmine.edu/tietjen/AnimalDiversity/bi
valvia01.gif
Gastropoda
 Ex. Snail
http://en.academic.ru/pictures/enwiki/83/SnailWA_edit02.jpg
Cephalopoda
 Ex. Octopus
http://chemistry.csudh.edu/faculty/jim/cozaugo4600/octopus.jpg
Scaphopoda
 Ex. Tusk Shell
Polyplacophora
 Ex. Chiton
http://www.rakbankerd.com/kaset/Animal/632_1.jpg
http://pt-lobos.com/images/lined_chiton_2c.jpg
Aplacophora
 Ex. Epimenia australis
http://www.whoi.edu/science/B/aplacophora/epimenia.jpg
Body Plan
 Visceral mass contains digestive,
excretory, and reproductive organs
 Locomotion primarily done with
muscular foot
 Some have a differentiated head
 The mantle is comprised of folds that
arise from the dorsal body wall that
enclose the cavity between the folds
themselves and the visceral mass
 Bivalve mollusks have two shells
Feeding
 Radula used for feeding consists of thousands
of microscopic chitinous teeth
 Gastropods(Snails/relatives) use the radula to
scrape food and then convey the food to the
digestive tract.
 Other gastropods use a modified radula as a
drill to drill through shells of oysters and other
creatures.
 Has a closed digestive tract that goes from the
mouth to the stomach to the intestine to the
anus
Respiration
 The mantle is a heavy fold of tissue wrapped around
the body of the mollusk
 the space between the mantle and the actual body is
called the mantle cavity
 This cavity in some mollusks acts as a lung
 In other mollusks, it contains gills that capture the
oxygen from the water when the water passes
through the cavity
Circulation
 All mollusks except cephalopods have an open
circulatory system which blood flows freely
throughout the body
 The mollusk heart has there chambers: Two atria
and one ventricle
 Cephalopods have a closed circulatory system with
blood vessels that carry the blood to all parts of the
body and then diffuse it
Excretion
 Nitrogenous wastes expelled by two tubular
structures called nephridia
 Each has an open funnel, nephrostome, lined with
cilia
 Coiled tubule runs from nephrostome to bladder,
which connects to excretory pore
 Wastes are gathered by nephridia from coelom and
discharged into mantle cavity
 Then are expelled by cavity by continuous gill
pumping
Response
 If carnivore, it can used chemosensory structures to
locate prey.
 Gastropods have tentacles with eyes on the end.
 Cephalopods have highly developed nervous systems.
 Brains unique among mollusks
 Many exhibit complex patters of behavior/high level of
intelligence
 Very elaborate eyes, similar to vertebrate eyes
Movement
 Their foot is their primary mechanism of locomotion
 Some mollusks secrete mucus, forming a path that
they glide along on their foot
 Cephalopods have foot which is divided into arms, also
called tentacles.
 In some pelagic forms, mollusks that are perpetually
free swimming, the foot is modified into wing-like
projections or thin fins
Reproduction
 Has distinct male/female individuals
 Few bivalves/many gastropods are hermaphroditic
 Cross fertilization is most common
 Most aquatic mollusks engage in external
fertilization
 Gastropods often have internal fertilization
Works Cited
 Bunje, Paul . "The Mollusca." University of
ca.
California Museum of Paleontology. UCMP,
2003. Web. 19 Apr 2010. <http://www.ucmp.
berkeley.edu/taxa/inverts/mollusca/mollus
php>.
 "Gravysnail." Youtube. Web. 19 Apr 2010.
 Raven, Peter and George Johnson. Biology. 6th
ed. NY: McGraw-Hill, 2002. 900-905. Print.
 "Phylum Mollusca: Mollusks ." The Diversity of
Life. N.p., n.d. Web. 19 Apr 2010. <http://
infusion.allconet.org/webquest/PhylumMo
llusca. html>.
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