Invertebrates 1

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Invertebrates 1

• Introduction, Porifera, Cnidaria

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Lecture outline

• Overview Invertebrate lectures
• What is an animal?
• Introduction to major phyla in Kingdom Animalia
• Basic phylogeny of Kingdom Animalia
• Phylum Porifera
• Phylum Cnidaria

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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

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2. What is an animal?

• Eukaryotic
• Multicellular Multiple cell types (Not just
  many cells)
• Heterotrophic
• No cell wall
• Characteristics of early development (unique!)
• Blastula and gastrula stages unique to animals
• Sponges, have precursors to these stages

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Phylum Porifera sponges
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Phylum Cnidaria Have Cnidocytes
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Phylum CtenophoraThe comb jellies
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Phylum PlatyhelminthesThe flatworms
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Phylum NematodaThe roundworms
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Phylum AnnelidaThe segmented worms
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Phylum MolluscaThe soft-bodied animals
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Phylum ArthropodaJointed appendages
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Phylum EchinodermataSpiny-skinned
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Phylum ChordataAnimals with notochords
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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

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Phylogenetic overview (traditional)
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Multicellularity separates the ancestral protists
from all animals

• Multicellularity
• Different types of cells!

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Development of two true tissue layers

• Separates Phylum Porifera from all others
• Sponges All other groups (2-3 tissues)

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Development of a third germ layer and bilateral
symmetry

• Cnidarians, Ctenophores All others
• Radial symmetry, 2 layers Bilateral
  symmetry, 3 layers
• (Porifera)

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Further developments (briefly)
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Body cavities

• Acoelomate
• Pseudocoelomates
• Coelomates

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Further developments (briefly)
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5. Phylum Porifera The sponges
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Evolutionary relationships

• Simplest multicellular animals
• Main cell type, choanocyte, resembles
  choanoflagellate cell
• Considered "multicellular" rather than colonial,
  because there are different cell types.
• Not much, if any cooperation between cells
• No real "tissues", no "systems" of any type (no
  nervous system, circulatory system, etc.)

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Sponge structure

• Review key parts

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Water movement and feeding

• Role of flagellum
• Role of collar
• Movement of particles
• Phagocytosis

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Protection

• Sponges are sessile
• 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)

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Phylum Cnidaria
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Evolutionary relationships

• Diverge from the Porifera in the following ways
• Diploblastic two true tissue layers
• Ectoderm and endoderm
• No mesoderm
• Radiata One of two phyla to exhibit radial
  symmetry

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Where Cnidarians fit in

• Cnidarians, Ctenophores All others
• Radial symmetry, 2 layers Bilateral
  symmetry, 3 layers
• (Porifera)

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Body organization

• Polyps and medusae

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Key features

• Polyps and medusae
• Tissue layers
• Ectoderm, gastroderm (endoderm)
• Mesoglia
• Secreted from the tissue layers
• Gastrovascular cavity
• Functions
• Not a true body cavity!
• Nervous system nerve net
• No other major body systems
• Tentacles with cnidocytes (stinging cells)

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Nervous system features

• True neurons
• Conduction can be unidirectional or bidirectional
  along neurons
• Nerve net with no direct pathways
• Have simple sensory organs

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Cnidocytes/nematocystsHow do they work?
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Life-history strategies