BIOL 111 Lecture Notes - Lecture 55: Symmetry In Biology, Nematode, Cephalization

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23 Jul 2016
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BIOL 111 Organismal Biology
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!EVOLUTIONARY INNOVATION: evolution of body cavity
Protostomes
!three major groups of protostomes:
o!arrow worms (no studied in this course)
o!lophtrochozoansmove using cilia at one point in their lives
!!loph” = tuft
!!“troch” = wheel
!!larval form of some lophtrochozoans are trochophores
!they have a tuft of cilia at the top and a band of cilia around the
middle
o!ecdysozoansmolt exoskeleton
Nematodes
!nematodes are roundworms
!they have a tapered posterior end and a blunt anterior end
o!exhibits cephalisation and bilateral symmetry
!nematodes are ecdysozoan
o!they have a thick, flexible cuticle that allows diffusion of gases that they molt
several times
!they have longitudinal muscles
o!they have little control over movement and therefore move by thrashing
!nematodes are pseudocoelomates
Nematode Diversity
!25000 species are known (but there is probably up to 1 million)
o!they have very specific habitats
!nematodes are terrestrial (soil) or aquatic
!they are free-living (scavengers, predatory) or parasitic
!they are extremely abundant
!e.g. Caenorhabitis elegans
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