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  • April 19, 2021
  • 8
  • 2019/2020
  • Class notes
  • Annette tavares
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Animal Diversity (Part 2) Lecture

Textbook Reference: Chapter 44 in Biology How Life Works (2nd ed.)
 Section 44.3; pp.956 to 963


Bilaterians
• Most animals belong to this group
• Based on embryo formation and molecular sequence data
• Bilaterians form two major groups: protostomes + deuterostomia
• Bilaterian characteristics:
 Bilateral symmetry
 Complex organs that develop from a triploblastic (3 germ layer) embryo
 Anatomical complexity of bilaterian animals allows for types of locomotion,
feeding, gas exchange, behavior, and reproduction unknown in earlier
branching groups


• Protostome animals can be further divided into two groups (based on molecular
sequence data):
1. Lophotrochozoa
2. Ecdysozoa



Lophotrochozoans
• Where does the name come from?
– Lophophore – ciliated crown of tentacles used for
feeding


– Trochophore larva – have a tuft of cilia on top and
additional cilia bands around middle


***Some members of group have neither of these
characteristics


1

, Lophotrochozoan diversity:
Phylum Description/Characteristics
Platyhelminthes - Live in marine, freshwater and damp
terrestrial habitats
- Flattened dorsoventrally
- Have a gastrocascular cavity with 1
opening
- Triploblastic
- Acoelomates
- No circulatory system
 Fine branches of gastrovascular
cavity distribute food direvtly to
cells
Parasitic - Nearly all free-living and mostly marine
Platyhelminthes - Some live as parasite in or on other
animals
 Parasitize a wide range of hosts
 Often have complex life cycles with
alternating sexual and asexual
stages
 Some require intermediate hosts
 Many have suckers for attachment
to their host
 Tough covering protects these
parasites
 Reproductive organs nearly fill
interior of these worms
- Tapeworms are parasitic and lack a
digestive system
 Adults live mostly in vertebrates,
including humans
 Long series of proglottids, sacs of
sex organs, lie posterior to scolex
 Tapeworms absorb food particles
from their hosts




More lophotrochozoan diversity:
2

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