Aquatic Mandibulates

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Aquatic Mandibulates

• Chapter 19

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Subphylum Crustacea

• Crustaceans, subphylum Crustacea typically have
  biramous, branched, appendages that are
  extensively specialized for feeding and
  locomotion.

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Subphylum Crustacea

• Crustaceans are the only arthropods that have two
  pairs of antennae.
• They also have a pair of mandibles (jaw-like
  appendages) and two pairs of maxillae on the
  head.
• Each body segment usually has one pair of
  appendages.
• Ancestrally biramous except for the first
  antennae.

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Subphylum Crustacea

• The ancestral condition in arthropods is to have
  many body segments.
• Fewer segments and increased tagmatization is the
  derived condition.

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Class Malacostraca

• Malacostracans usually have a head with 5 fused
  segments, a thorax with 8 segments and an abdomen
  with 6.
• Anterior rostrum
• Posterior telson

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Class Malacostraca

• Decapods order decapoda are all relatively
  large crustaceans and include lobsters, crabs,
  crayfish, and shrimp.
• 3 pairs maxillipeds 5 pairs walking legs.
• Harder, heavy plates in larger crustaceans due to
  calcareous deposits in addition to chitin.
• The carapace covers much or all of the
  cephalothorax.

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Class Malacostraca

• Arthropods have a true coelom, but it is much
  reduced and the major body space is the blood
  filled hemocoel (derived from the blastocoel).
• Open circulatory system
• Gas exchange occurs across thin areas of the
  cuticle or in gills.

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Class Malacostraca

• Most crustaceans have separate sexes.
• Many brood eggs, in special chambers or under
  their abdomens carried by abdominal appendages.

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Class Malacostraca

• Crayfishes have direct development.
• In most crustaceans, there are larval forms.
• Nauplius ancestral, widely occurring larval
  form.

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Class Malacostraca

• Krill order Euphausiacea planktonic
  shrimp-like animals.
• Most are bioluminescent with a light producing
  organ called the photophore.
• Krill are eaten by whales.

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Class Malacostraca

• Other orders of malacostracans include
• Isopoda including pill bugs.
• Compressed dorsoventrally.
• Amphipoda many marine, terrestrial freshwater
  forms.
• Compressed laterally.

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Class Branchiopoda

• Includes three orders
• Anostraca fairy shrimp and brine shrimp, no
  carapace.
• Notostraca tadpole shrimp, carapace forms a
  large dorsal shield.
• Diplostraca water fleas carapace encloses
  body but not head.

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Class Branchiopoda

• Phyllopodia legs that serve as respiratory
  organs.
• Legs may be used for filter feeding and
  locomotion as well.
• Mostly freshwater forms.

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Class Branchiopoda

• Water fleas (like Daphnia) produce females
  parthenogenetically in summer. Males are produced
  when unfavorable conditions arise and
  overwintering fertilized eggs are produced that
  are resistant to cold and desiccation.

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Class Ostracoda

• Ostracods are enclosed in a two part carapace and
  look a bit like a clam.
• Marine or freshwater.
• Mostly benthic.

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Class Maxillopoda

• Maxillopods generally have 5 cephalic, 6
  thoracic, and 4 abdominal segments plus a telson.
• Reductions common.
• The nauplius of maxillopods has a maxillopodan
  eye unique to this group.

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Class Maxillopoda

• Planktonic crustaceans include many species of
  copepods (subclass Copepoda) which are among the
  most numerous of all animals.
• They lack a carapace.
• Retain the simple maxillopodan eye in adults.
• Antennules used in swimming.
• Very diverse.

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Class Maxillopoda

• Barnacles subclass cirripedia are a group of
  mostly sessile crustaceans whose cuticle is
  hardened into a shell.
• Their legs are long, many jointed cirri that
  extend out through the calcareous plates to
  filter feed.

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Class Maxillopoda

• Barnacles are hermaphroditic.
• Most hatch as a nauplius larva then become a
  cyprid larva (resembles the ostracod Cypris).
• Cyprids attach to the substrates and begin
  secreting calcareous plates.