Download Invertebrates 1

Biology 212, Invertebrates 1
February 25, 2004
I.
II.
III.
IV.
V.
Overview of invertebrate lectures
A.
Examine evolutionary relationships among the animal phyla.
B.
Examine basic body plan
C.
Examine selected aspects of life-history and ecology
What is an animal? Five characteristics (only one is really unique.)
Kingdom Animalia: Introduction to the major phyla
Phylogeny overview for Kingdom Animalia
A.
Monophyletic (?)
1.
Hypothesis: Kingdom Animalia evolved from a choanoflagellate[Fig.
32.2, 32.3]. Supported by recent molecular evidence.
2.
Alternate hypthesis: Kingdom Animalia is polyphyletic
B.
First branch point: Multicellularity separates the most simple animals
(Phylum Porifera, the sponges) from their presumed protist ancestors.
C.
Key branch points and their adaptive significance —Traditional view [Fig. 32.4]
1.
Development of two true tissue layers: ectoderm and endoderm
a)
Separates Porifera from the rest of the animal phyla

Significance?
2.
Development of a third germ layer (the mesoderm) and bilateral symmetry
a)
Separates Cnidaria (and Ctenophora) from rest of animal phyla

Significance?
3.
Development of a body cavity [Fig. 32.6]
a)
Separates Platyhelminthes from the rest of animals
b)
A "body cavity" is a space between the gut and the body wall

Significance?
4.
Development of a "true" coelom, completely lined with mesoderm (both
inside of body wall and outside of gut)
a)
Separates nematodes (and some other phyla) from the rest.

Significance?
D.
Focus on the Coelomates
1.
Protostomes and Deuterostomes: two distinct groups which differ in three
important ways developmentally [Fig. 32.7]—go through figure later
Phylum Porifera: the "pore bearers" or sponges
A.
Sponge diversity (slides)
B.
Evolutionary relationships
1.
Why considered an animal?
2.
How different from other groups?
C.
Structure of a simple sponge [Fig. 33.3]
1.
Know basic parts
2.
choanocytes: key cell type
a)
Basics of water movement
b)
Basics of feeding.
D.
Sponge sex (are you ready for this?)--briefly
E.
Protection
1.
Think about the fact that sponges are sessile, cannot run away (similar
problems as faced by plants...) So, what are some strategies? (Several…)
2.
F.
VI.
Like plant secondary compounds, "toxins" in sponges are appear to have
pharmaceutical uses:
a)
Anti-cancer, anti-viral
Movement
1.
Most sponges are sessile after settlement, but there is an exception:
Phylum Cnidaria ("cnid" = nettle)
A.
Evolutionary relationships
1.
Diverge from the Porifera in the following ways:
a)
Diploblastic: two tissue layers (germ layers are ectoderm and
endoderm) [Significance?]

No mesoderm
b)
Radiata: One of two key phyla to exhibit radial symmetry
B.
Body organization [Fig. 33.4]
1.
Polyps and medusae
2.
Ectoderm, gastroderm (=endoderm)
3.
mesoglia: jelly-like, excreted from the other tissue layer
a)
No mesoderm = no true muscles; epithelium is modified to
contract.
4.
Gastrovascular cavity
a)
Several functions…
5.
Tentacles with cnidocytes (stinging cells)
6.
Nervous system: nerve net
7.
No other major body systems
C.
Focus: the cnidocyte [Fig. 33.5]
1.
Structure
a)
Location.
b)
The nematocyst (some details of its structure)
c)
The operculum keeps it trapped inside
d)
Trigger mechanism
2.
Function
a)
Stimulation of the trigger, mechanically or chemically, causes
nemetocyst to forcibly evert
b)
Nematocysts can deliver a "triple whammy" to the victim

What three effects does it have?
D.
Nervous system: nerve net
1.
true neurons
2.
conduction can be unidirectional or bidiretional
3.
Forms a net with no direct pathways and no brain
4.
Nerve signals travel in waves.
5.
Have simple sensory organs:
E.
Cnidarian life-history strategies
1.
Alternation of polyp and medusa forms [Fig. 33.7]
a)
Basics of alternation (sexual vs. asexual reproduction)
b)
Adaptive value of polyps vs. medusae
c)
Which Cnidarians do this, and which don’t?