Invertebrates

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Chapter 33 Invertebrates
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Two views of animal phylogeny Which is right?
Both are useful?
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Parazoa Phylum Porifera  Sponges   1. 
Non-moving (sessile) animals 2.  No nerves or
muscles (no tissue differentiation) 3.  Mostly
marine 4.  Filter feeders  Collect food
particles from water 5.  Most sponges are
hermaphrodites.  Hermaphrodites function as both
male and female in sexual reproduction by
producing eggs and sperm.   All other animals
are in the clade Eumetazoa (true tissues).
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Animals probably evolved from colonial,
flagellated protists, like this choanoflagellate
colony.
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Cnidarians Polyp and medusa forms of
cnidarians.   Radial symmetry with central
digestive (gastrovascular) cavity.   One opening
in the gastrovascular cavity serves as both mouth
and anus.                        
Carnivores. Phylum name comes from specialized
cells called cnidocytes.  Cnidocytes are
stinging cells used for defense and to capture
prey.
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Purple striped jelly, Pelagia panopyra
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Polyps Sea anemones
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Phylum Ctenophora The Comb jellies        Resembl
e cnidarian medusas.   Use cilia for locomotion.
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Protostomia  Lophotrochozoa Phylum
Platyhelminthes  Flatworms                       
  Sizes range from microscopic up to 20 meters
long (tapeworms).   Many are parasites.  
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Class Turbellaria (flatworms)                     
                            i.  Mostly
free-living (non-parasitic) ii.  Feed on small
animals, dead animals iii.  Very flat for O2
exchange.  They have no gas exchange
organs.                        
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Classes Monogenea/Trematoda                       
                         i.  Live as
parasites ii.  Trematodes parasitize
vertebrates.  For example, humans but often
with intermediate hosts.   
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The life history of a blood fluke (Schistosoma
mansoni).
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Class Cestoidea Tapeworms                      
                           i.  Live as
parasites ii.  Head contains suckers and hooks
that lock onto the intestinal lining of the
host. iii.  The rest of the body is mostly units
called proglottids that are sex organs. iv.  Eggs
transferred to new hosts by consuming fecal
contaminated water.  
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Anatomy of a tapeworm
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Phylum Rotifera  Rotifers                        
Aquatic Sizes range from 0.5 to 2 mm Complete
digestive tract  
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A rotifer
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Lophophorate Phyla  Bryozoans, Phoronids,
Brachiopods                         All of these
groups have a lophophore.  The lophophore is a
horseshoe shaped fold near the mouth that is
surrounded by ciliated tentacles.   Bryozoans
resemble mosses.    - They have a hard
exoskeleton.            - They are important as
reef builders. Phoronids are marine
worms.   Brachiopods resemble clams.     
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A bryozoan
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A brachiopod
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Phylum Nemertea  Proboscis (ribbon)
worms              Up to 30 meters in
length   These worms have a hydraulically-operated
proboscis that is used to capture prey. Closed
circulatory system.
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Nemertea Proboscis worms
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Phylum Mollusca  Mollusks                        
Snails, clams, octopi, squids, oysters   There
are at least 150,000 known species   All mollusks
have similar body plans a.  Muscular foot b. 
Visceral mass with organs            c.  Mantle
that secretes the shell
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Bivalvia Shells divided into two parts.  Gills
are used for feeding and gas exchange. Example 
Clams, oysters
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Dreissena polymorpha Zebra mussel
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Cephalopoda Rapid movement well-developed
nervous systems.  Example  Octopus, squid,
nautilus  
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Phylum Annelida  Segmented worms                 
        Sizes range from 1 mm to 3 meters in
length.   Each segment contains a pair of
excretory tubes called metanephridia.   Annelids
are hermaphrodites that cross-fertilize.   Three
classes a.  Oligochaeta earthworms
           b.  Polychaeta mostly
marine            c.  Hirudinea leeches  
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Protostomia  Ecdysozoa             Phylum
Nematoda  Roundworms Non-segmented Some are
important parasites of animals.                   
                  Pinworms and hookworms, e.g.,
Trichinella, obtained by eating undercooked pork
juveniles infect all body organs and tissues.  
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Nematodes
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Phylum Arthropoda  Arthropods (crustaceans,
spiders, insects)             Hard exoskeleton,
segmented bodies, jointed appendages            
Arthropods are the most successful of all animal
phyla based on diversity, distribution, and
numbers.   Nearly one million species identified
so far, mostly insects.   The exoskeleton, or
cuticle, is composed of protein and
chitin.   Molting of the cuticle is called
ecdysis.   Extensive cephalization.   Open
circulatory systems in which a heart pumps
hemolymph through short arteries and into open
spaces (sinuses). Aquatic members- gills for
gas exchange terrestrial members- tracheal
system of branched tubes leading from surface
throughout body.
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Four evolutionary arthropod lineages              
                       a.  Trilobites
extinct b.  Chelicerates horseshoe crabs,
spiders c.  Uniramians centipedes, millipedes,
insects d.  Crustaceans crabs, lobsters,
barnacles  From these lineages arose five major
classes of arthropods.          
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Insecta (insects) Outnumber all other forms of
animals. Evolved flight during Carboniferous
period.  Flight was followed by an explosion of
diversity. Coevolution of flowering plants and
insects. Wings are extensions of the
cuticle. Waste is removed from hemolymph by
excretory organs called malpighian tubes.
  Nervous system has a pair of ventral nerve
chords that join in the head to form a cerebral
ganglion (brain) that is close to the sensory
organs in the head (cephalization).  
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• Note Many insects undergo metamorphosis during
  their development.
• Incomplete metamorphosis is a process whereby the
  young look like the adults, but have different
  body proportions.
• Complete metamorphosis is a process where the
  larval stages (larva, maggot or grub) are
  specialized for eating.
• The adult stage is specialized for reproduction
  and dispersal (e.g. flight).
• The process of metamorphosis occurs during a
  pupal stage.

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Class Crustacea E.g., crabs, lobsters          Al
most all are aquatic. Ca. 40,000
species.             Includes krill eaten by
whales, and daphnia, copepods, amphipods in
Lake Erie, pill bugs, etc.
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Deuterostomia Phylum Echinodermata
(Echinoderms) Water vascular systems network of
hydraulic canals used for locomotion, feeding,
and gas exchange.  It extends into tube feet that
are used for locomotion and feeding. Echinoderms
appear to be radial, but are bilateral in larval
stages.
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