Download Topic 19

Biol 1309
Invertebrates
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So- what is an invertebrate?
• No backbone!
• Way more of these
than vertebrates
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Historical View
• Few fossils for some
because of soft
bodies  jelly fish
and sponges
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Historical- (cont.)
True
animals
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More recently, hard bodies left good fossils! (575 Million
years!)
Closest relative to protist is the choanoflagellate.
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The order of things! (see next slide)
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Protists
Choanoflagellates
Porifera -- Sponges (no “tissues”, metazoa)
Eumetazoan (true)
Bilateria
Deuterostomes (unusual embryonic
development)
• Lophotrochozoa
• Ecdysozoa
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Porifera? - metazoa?
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Sessile
No tissues or organs
Radial or no symmetry
Silica skeleton
Filter feeders
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Cnideria
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Jellies, cubozoans, corals, hydroids, sea anemones
Radial, hydrostatic skeletone
Medusas, polyps
Single digestive opening
2 cell layers!
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The Cnideria life cycle
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The Cnidaria (w/ nematocysts)
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Platyhelminthes
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Flatworms
Flukes
Tapeworms (flat-segmented)
All bilateral
Gastric cavity w/branching, single opening
Hydrostatic skeleton
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Example Playhelmithes
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So what next to proceed?
• The next amazing
development is the
coelom!
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Coelom? What is it?
• Fluid-filled cavity separating body wall
muscles from muscles of digestive tract,
allows:
– Digestion independent of body movement
– Primitive fluid circulation for internal body
– Folding is possible (useful!)
– Leaves room for true circulatory
– The anus is invented!
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The coelom plan
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The three
coelom forms
that give rise
to all other
plans!
(the layer plan
for embryonic
development!)
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The Mollusca phylum
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Slugs, snails, octopus, squid, oyster etc.
No segments, w/mantle
Shell or rudimentary shell
Head and foot regions
Bilateral, coelom and complete digestive
system
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Annelid phylum
• Segmented worms, earthworms,
polychaetes, leeches
• Repeated body segments
• Gas exchange through skin or gills
• Bilateral, coeloms, hydrostatic!
• Interesting new structures:
– Clitellum
– Reduced head
– setae
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Example Annelids
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Arthropoda phylum
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Largest animal group
Jointed exoskeletons
Segmentation
Chitin exoskeleton
Many many groups
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Example Arthropods
• Horseshoe crabs (cephalothorax + abdomen, 5 leg pairs)
• Spiders & Scorpions (cephalothorax + abdomen, 4 leg
pairs)
• Millipedes (head, antennae, mouth parts, segmented, 2 leg
pairs/segment, vegetarians)
• Centipedes (head, antennae, mouth parts, segmented, 1 leg
pair/segment, predators w/venom)
• Crustaceans (cephalothorax + abdomen, 2 antennae pairs,
mouth parts, 4 or more legs, some appendages)
• Insecta (head, thorax, abdomen, antennae, 2 wing pairs, mouth parts,
3 leg pairs
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Take a look at Circulatory Systems
• Two main kinds: Open or Closed
• Most systems composed of:
– Pump
– Vessels
– Fluid
• Open: mollusks, arthropods
• Closed- most everyone else…
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Circulatory Systems
Instead of Blood
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Side by side…
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Differences
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Pressure
Blood flow rate
Body size differences
Fluid:
– Hemolymph mixes into coelom and then
back…
– Blood moves continuously
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