Invertebrates

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Phylogeny of Extant Phyla
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Phylum Porifera
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Porifera Characteristics

• Sponges
• Sole member of the Parazoa
• Lack true tissues, Simplest of Animals, no nerves
  or muscles
• Choanocytes (collar cells) ? Unique flagellated
  cells that ingest bacteria and tiny food
  particles
• Choanocytes look a lot like Choanoflagellates
• Amoebocytes transfer food to rest of cells
• Adults sessile, larvae non-sessile
• Cells tend to be totipotent (retain zygotes
  ability to form the whole animal)

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Choanocytes
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Amoebocytes
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Anatomy of Simple Sponge
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A More Complex Sponge
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Phylum Cnidaria
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Cnidaria Characteristics

• Hydras, Jellies, Sea Anenomies, Corals
• One member of the Radiata (also Ctenophora)
• Diploblastic, Carnivorous, Tentacled
• Lack true muscles (since no mesoderm)
• Possess nerve net
• Cnidocytes ? Cells that shoot stinging or
  grasping threads at potential prey
• Grastrovascular cavity (only one opening)
  Hydrostatic Skeleton
• Polyps vs. Medusa

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Cnidocytes
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Cnidaria Anatomy
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Class Hydrozoa
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Class Scyphozoa
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Class Anthozoa
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A Cnidarian Life Cycle (Obelia)
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Phylum Platyhelminthes
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Platyhelminth Characteristics

• Flatworms (including Flukes and Tapeworms)
• Bilaterally symmetrical acoelomates
• Flat, unsegmented, single opening to
  gastrovascular cavity
• Eyespots, flaps on head involved in sense of
  smell
• No circulatory system (instead diffusion)
• Tapeworms have no digestive system
• Use ventral cilia to locomote across surfaces
  (but some can swim)
• Cephalized, have nervous system

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Planarian Anatomy
Class Turbellaria
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Fluke Lifecycle
Class Trematoda
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Tapeworm Anatomy
Class Cestoidea
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Phylum Rotifera
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Rotifer Characteristics

• Rotifers
• Very small animals
• Possess complete digestive tract
• Pseudocoelomates
• Aquatic, essentially serve as animals that
  approximate the protozoan niche

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Phylum Nematoda
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Nematode Characteristics

• Round worms (including pinworms hookworms)
• Pseudocoelamates, complete digestive tracts
• There are many free-living nematodes as well as
  some parasitic nemotodes
• Includes Caenorhabitis elegans, a very important
  research organism to developmental biology

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A Roundworm
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Phylum Mollusca
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Mollusk Characteristics

• Snails, Slugs, Clams, Squids, Octopi, etc.
• Class Gastropoda, Class Bivalvia, Class
  Cephalopoda, etc.
• Protostomes
• Basic body plan built around a muscular foot, a
  visceral mass, and a mantle
• Not all mollusks have a shell
• Mollusks lack segmentation
• Most have Open Circulatory System
• Some (cephalopods) have Closed Circulatory System

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Class Polyplacophora (chitons)
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Class Gastropoda
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Class Bivalvia
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Class Bivalvia
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Class Cephalopoda
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Closed vs. Open Circulation
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Phylum Annelida
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Annelid Characteristics

• Segmented worms (earth, marine, leeches)
• Class Oligochaeta (I.e., earth worms), Class
  Polychaeta (e.g., clam worms), Class Hirudinea
  (I.e., leeches)
• Protostomes, Body segments, Closed circulatory
  system

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Class Oligochaeta
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Class Polychaeta
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Class Hirudinea
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Phylum Arthropoda
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Arthropod Characteristics

• Insects, Crustaceans, Spiders, Scorpions,
  Horseshoe crabs, Millipedes, Centipedes, Ticks,
  Mites, etc.
• Protostomes with segmented bodies, jointed
  appendages, and hard (chitinous) exoskeletons
• Also have well-developed senses and open
  circulation
• Note that the taxonomy of the arthropods is in
  some turmoil and we will try to split the
  difference by describing phylum Arthopoda as a
  Superphylum
• What previously were subphyla as phyla

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Phylum Trilobita
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Phylum Chelicerata
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Phylum Uniramia
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Phylum Crustacea
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Phylum Echinodermata
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Echinoderm Characteristics

• Sea stars, brittle stars, sea urchin, sea lilies,
  sea cucumbers
• Coelomates, Deuterostomes
• Multiple arms, tube feet, water vascular system,
  calciferous endoskeleton
• Radial symmetry, but radial symmetry likely
  derived (i.e., not radiata)
• Larvae are bilaterally symmetrical

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• All 7,000 or so species of echinoderms are
  marine.
• Examples are
• sea stars
• brittle stars
• sea urchins
• sea lilies and feather stars
• sea cucumbers
• sea daisies
• sand dollars

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Starfish Anatomy
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Tube feet
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Phylum Chordata
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Link to Next Presentation
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Acknowledgements
http//boxes.geneseo.edu/Biology/odonnell/Biol201
19,20S2003/