Invertebrates 1
Introduction, Porifera, Cnidaria
Lecture outline
1. Overview: Invertebrate lectures
2. What is an animal?
3. Introduction to major phyla in
Kingdom Animalia
4. Basic phylogeny of Kingdom
Animalia
5. Phylum Porifera
6. Phylum Cnidaria
1. Overview of Invertebrate
portion of course
 Evolutionary relationships
 Body plan
 How animal meets its basic needs
 Relationship of structure and function
 Selected aspects of life-history and
ecology
2. What is an animal?
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Eukaryotic
Multicellular: Multiple cell types (Not just many
cells)
Heterotrophic
No cell wall
Characteristics of early development (unique!)
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Blastula and gastrula stages unique to animals
Sponges, have precursors to these stages
Phylum Porifera: sponges
Phylum Cnidaria:
Have Cnidocytes
Phylum Ctenophora:
The comb jellies
Phylum Platyhelminthes:
The flatworms
Phylum Nematoda:
The roundworms
Phylum Annelida:
The segmented worms
Phylum Mollusca:
The “soft-bodied” animals
Phylum Arthropoda:
Jointed appendages
Phylum Echinodermata:
Spiny-skinned
Phylum Chordata:
Animals with notochords
4. Phylogenetic overview
 Presumed to be monophyletic
 Hypothesis assumes all animals evolve from a
single common ancestor
 That ancestor thought to be a sponge-like protist
called a choanoflagellate
 Modern choanoflagellate
 Found in aquatic habitats
 Some propose
polyphyletic origins
 Cite Cambrian explosion
Phylogenetic overview (“traditional”)
Multicellularity separates the
ancestral protists from all animals
 Multicellularity
 Different types of cells!
Development of two true
tissue layers
 Separates Phylum Porifera from all
others
 Sponges
All other groups (2-3 tissues)
Development of a third germ
layer and bilateral symmetry
 Cnidarians, Ctenophores
 Radial symmetry, 2 layers
 (Porifera)
All others
Bilateral symmetry, 3 layers
Further developments
(briefly)
Body cavities
 Acoelomate
 Pseudocoelomates
 Coelomates
Further developments
(briefly)
5. Phylum Porifera: The
sponges
Evolutionary relationships
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Simplest multicellular animals
Main cell type, choanocyte, resembles
choanoflagellate cell
Considered "multicellular" rather than
colonial, because there are different cell
types.
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Not much, if any cooperation between cells
No real "tissues", no "systems" of any type (no
nervous system, circulatory system, etc.)
Sponge structure
 Review key parts…
Water movement and
feeding
 Role of flagellum
 Role of collar
 Movement of
particles
 Phagocytosis
Protection
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Sponges are sessile…
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Toxins/warning coloration (this is why many
sponges are brightly colored)
Painful or sharp covering (spicules)
Regenerative ability
Camouflage (if not toxic)
Bore into shells.
NOTE: Nudibranch predators co-opt
sponge defenses (toxins, spicules)
Phylum Cnidaria
Evolutionary relationships
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Diverge from the Porifera in the
following ways:
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Diploblastic: two true tissue layers
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Ectoderm and endoderm
No mesoderm
Radiata: One of two phyla to exhibit radial
symmetry
Where Cnidarians fit in…
 Cnidarians, Ctenophores
 Radial symmetry, 2 layers
 (Porifera)
All others
Bilateral symmetry, 3 layers
Body organization
 Polyps and medusae
Key features
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Polyps and medusae
Tissue layers
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Mesoglia
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Secreted from the tissue layers
Gastrovascular cavity
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Functions
Not a true body cavity!
Nervous system: nerve net
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Ectoderm, gastroderm (=endoderm)
No other major body systems
Tentacles with cnidocytes (stinging cells)
Nervous system features
 True neurons
 Conduction can be unidirectional or
bidirectional along neurons
 Nerve net with no direct pathways
 Have simple sensory organs
Cnidocytes/nematocysts
How do they work?
Life-history strategies