Lake Tahoe Community College
Winter Quarter
Bio 212 Zoology
Instructor Sue Kloss
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Chapter 9 – Multicellular and Tissue Levels of Organization
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I. Intro - Origins of Multicellularity
A. Multicellular life has been on earth for 550 million years,
B. The evolutionary explosion that occurred in the 100 million yrs. prior to the Cambrian/Precambrian
C. colonial hypothesis
D. syncytial hypothesis
E. Are animals polyphyletic or monophyletic? The nearly simultaneous appearance of all animal phyla in
the early Cambrian makes it hard to tell
II. Phylum Porifera - Sponges
A. Primarily marine animals that consist of loosely organized cells
B. Characteristics of members of Phylum Porifera
C. Cell types, Body wall, and Skeletons
1. sponge cells are specialized for particular functions (division of labor)
D. spicules - needlelike spikes.
E. Water currents
1. body forms
a. ascon body form
b. sycon body
c. leucon body Maintenance functions
F, sponges feed on particles
1. range in size from .1 to 50 um.
2. feeding methods - choanocytes filter small suspended particles.
G. Reproduction - most sponges are monoecious - both sexes occur in same individual; do not usually
self fertilize because eggs and sperm ready at different times.
III. Phylum Cnidaria
A. Intro - Members of Phylum Cnidaria possess radial symmetry
1. there are > 9k spp of Cnidarians,
2. Characteristics
B. Body Wall and nematocysts
1. diploblastic tissue organization
2. ectoderm of embryo gives rise to epidermis
C. Alternation of Generations
D. Maintenance Functions
1. gastrovascular cavity
2. food of most cnidarians
3. nematocysts
4. water provides support
5. polyps use variety of locomotive forms
6. medusae move by swimming and floating
7. cnidarians have most primitive nervous elements in animal kingdom;
8. all gases and nitrogenous wastes exchanged by diffusion
E. Reproduction - most are dioecious - each has a particular gender.
F. Class Hydrozoa - hydras - small relatively common cnidarians; most marine, but some are freshwater characteristics: cnidocysts in epidermis; release sperm and eggs out of body
G. Class Scyphozoa - true jellyfish H. Class Anthozoa - anemones and corals
IV.
Phylum Ctenophora - comb jellies
Lesson Objectives and Study Questions Chapter 9.
1. Describe the 2 current hypotheses that explain the origins of animal multicellularity.
2. What are arguments for and against the hypothesis of monophyletic origin of animals?
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What are 4 defining characteristics of organisms in the phylum porifera?
Why is radial symmetry an advantage in free floating or sessile animals?
Name and describe the 3 general body forms of sponge categorization (e.g. ascon, etc)
List and describe the specialized cells types possessed by sponges.
What types of support systems do sponges have?
On what do sponges feed, and how do they eat?
How do sponges reproduce? What is a gemmule?
What characteristics of Cnidaria are most important in distinguishing it from other phyla?
Name the classes in the phylum Cnidaria, and provide a common name for an animal in each.
how has dimorphism (alternation of generations) diverged and developed in different cnidarian classes?
How does a nematocyst discharge, and what functions may it have? How is it related to a cnidocyte?
Describe the nervous system of Cnidarians.
How do Cnidarians eat and digest their food?
How do they exchange gases and nitrogenous wastes?
How do Cnidarians reproduce?
How is the Phylum Ctenophora distinguished from Phylum Cnidaria? Provide a common name for a
Ctenophoran.