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Lecture 26

BIOLOGY 207 Lecture 26: Bio 207 lecture 26Premium

2 pages20 viewsSpring 2017

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Bio 207 3/24/17
I. Phylum Ctenophora
a. Have bi-radial symmetry: not perfect radial symmetry; have rows of cilia that are radially
symmetric, but has only two tentacles
i. Part of body separated into right and left, rest radially symmetry
ii. Cnideria have true radial symmetry, so arose after ctenophore branch
b. Apomorphy: shared derived character
i. Bilateral symmetry is an example of this in the tree on slide 73, as anthozoa,
scyphozoan and hydrozoa which branch after ctenophora branch off
c. Have no cnidocysts
d. Holopelagic life cycle: no benthic phase
e. Have external fertilization
f. Choanoflagellida are outside animal kingdom but from them the porifera branches off, and
the next branch is the ctenophore
II. Phylum Platyhelminthes (flatworms)
a. Have bilateral symmetry: only one plane down which an organism can be cut in order to
get two mirror images
b. Move forward (which cannot exist for a radial organism), encounter environment with
same part of their body, this is a result of bilateral symmetry
i. Move via a set of cilia, though some swim
c. Class Turbellia
d. Free-living flatworms can be benthic or pelagic, they have also invaded land successfully
(but rare)
e. What we owe to flatworms:
i. Bilateral symmetry and forward movement
ii. Every organ system (except for one) that humans have
iii. Internal fertilization
f. Important consequence of bilaterality forward movement having a brain
i. For radial symmetry, cannot have all intelligence concentrated in one place
ii. Based on this theory, if an organism with forward movement became sessile, it
would lose its brain
g. Class Acoela: most primitive, basic flatworms that lack an excretory system
h. Has 3 embryonic layers, whereas porifera and cnidaria only had two
i. Ectoderm: epidermis and nerves, muscles
ii. Endoderm: makes digestive system, muscles also
iii. Mesoderm: novel layer for Platyhelminthes, so free to produce new cell types,
tissues and organs
i. The organ grade of organization: multiple cell types and tissues build a complex organ,
organs all come from mesoderm except brain and eyes (from ectodermal)
j. Excretory system comes from Mesoderm: allows organisms to get rid of waste without
relying on diffusion
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