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Phylum Mollusca

Biology
by

Katrianna Urrea

on 20 May 2014

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Transcript of Phylum Mollusca

Class
Bivalvia - clams, oysters, etc.
Class
Gastropoda - snails, slugs
Class Polyplacophora - the chitons
Clams and mussels formed shells and mantles as they grew
The shell may open slightly to breath, to feed, or to reproduce without exposing its entire body
It's assumed that the first molluscs are of the early Cambrian period
This is about 550 to 580 million years ago
The 5 Classes Of Mollusca
Mollusca Characteristics
Mollusca's Evolutionary Milestones
Phylum Mollusca
Class
Scaphopoda - tusk shells
Class
Cephalopada - Squid, Cuttlefish, Octopus
References
Includes around 600 extinct species.
Entirely marine species.
Can live up to 7000m deep.
A chiton is flat and elongated.
A chiton has a foot.
Has 8 overlapping shell plates
A chiton's head is small and lacks eyes and tentacles.
Structure
Largest group of molluscs
More than 62,000 species
Comprise about 80% of living molluscs
Diverse in size, body, & shell
Occupy all marine habitats
Structure
Structure
Possess a single, often coiled shell
There are approximately 900 species.
Found in marine regions.
Live in waters greater than 6m deep.
Have four layers, used for identification.
Most live buried in sediment or ice; "safe from predators"
There are 140 species known in the Arctic
Freshwater species are endangered
Stay where first settled; do not migrate
Around 650 to 700 extinct species
Strictly marine species, found in all worlds oceans.
They are the most complex class in phylum mollusca.
Cephalopoda means "head food". They have the most complex brain of the invertebrate.
Structure

Examples of
Animals :
Pylum Mollusca
Structure
Bilaterally symmetrical
Has a pair of kidneys
Has etenidial gills (gaseous exchange)

Reproduces sexually
circum-oesophagal ring
ganglia (cluster of nerves)
paired nerve chords
Nervous system
These types of molluscs crawled on the ocean floor and most likely did not possess a shell
Octopi
Squid
Cuttlefish
Snails
Slugs
Clams
Oysters
Chitons
Scallops
Sea Butterflies
Sea Hares
http://www.ucmp.berkley.edu/taxa/inverts/mollusca.php
http://animaldiversity.ummz.umich.edu/accounts/polyplacophora
http://www.ucmp.berkley.edu/taxa/inverts/mollusca/Gastropoda.php
http://animaldiversity.ummz.umich.edu/accounts/cephalopoda
http://www.tutorvista.com/content/biology/biology-iii/animal-kingdom/phylum-mollusca.php
http://www.biology-questions-and-answers.com/mollusca/html
http://sunny.moorparkcollege.edu/-~econnolly/mollusca.htm
http://www.evolutionnews.org/2013/11/cambrian_explos_2078971.html
http://www.molluscs.at/mollusca/index.html?/mollusca/shell.html
http://www.earthlife.net/inverts/mollusca.html
The shell then developed two separate halves that were held together by a ligament.
Bivalvia Class
Gastropoda Class
The shell of a snail is coiled either left or right to form a spiral shape
During their evolution, they developed a dorsal sack which holds the internal organs inside the shell
Torsion is the process of the shell coiling into a spiral
Scaphopoda Class
A tusk shell is specially adapted to burrow for food in the ocean ground
It is hollow and open on both ends; one is for the burrowing foot, and the other is for respiration
Cephalopoda Class
Cephalopods evolved with a reduction of the shell and a sacrifice of protection, but had improvement in their movability
Cuttlefish and squids have only an internal shell left
Octopuses have no shell left and are at the end of the evolutionary chain
Polyplacophora Class
They have several shell plates that overlap like a knight's armour instead of having spikes or scales
These plates improve protection
References
Chitons have a further development of evolution
http://en.m.wikipedia.org/wiki/Bivalvia
www.earthlife.net/inverts/mollusca.html
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