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Animal Diversity (Part 2) LectureTextbook 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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