Protostome Animals

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Protostome Animals

• Chapter 32

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Protostome Animals

• Protostomes are bilaterally symmetric, coelomate
  animals
• Undergo early development differently than
  deuterostomes
• Contains the most successful phylum, Arthropoda
  and some very obscure phyla, Echiura ( about 135
  species)
• Phyla have distinct body plans, feeding
  apparatuses, and locomotions

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Why Do Biologists Study Protostomes?
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Arthropods

• Most diverse and numerous phylum of animals
• 925,000 known and identified
• Live in almost every know habitat
• Cause important diseases

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Crustaceans and Mollusks

• Crustaceans and mollusks are consumers,
  predators, and scavengers in many marine food
  chains
• They are among the most expensive and
  sought-after seafood

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Insects, Spiders, and Mites

• Insects eat about a third of the crops planted by
  farmers
• They are the most economically important group of
  protostomes
• Dominant consumers, predators, and scavengers in
  all terrestrial ecosystems
• Most flowering plants are pollinated by insects

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How Do BiologistsStudy Protostomes?
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How Do Biologists Study Protostomes?

• Based on data obtained from
• morphology studies
• the fossil record
• molecular phylogenies

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Protostome Early Development

• Researchers have drawn some general conclusions
  about protostomes
• Protostomes undergo spiral cleavage after
  fertilization.
• During gastrulation, the initial invagination
  that forms in the embryo becomes the mouth.
• A body cavity, or coelom, may form within blocks
  of mesodermal tissue.

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Protostome Symmetry

• Protostomes are bilaterally symmetric
• Have a distinctive head and posterior region.
• All protostomes have three embryonic tissues.

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Protostome Segmentation

• Some protostomes may exhibit segmentation
• Their bodies have a series of compartments with
  repeated structures.

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Prehistoric Protostomes

1. Most protostome phyla first appear in the Burgess
   Shale faunas, dated at about 525515 million
   years ago

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Protostomes are Monophyletic

• Molecular phylogenies support the hypothesis that
  protostomes are a monophyletic group
• A branching event occurred within the lineage,
  producing two groups
• the Lophotrochozoa and the Ecdysozoa.

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Analyzing Morphological Traits
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Coelom Development

• Radical changes occurred in coelom formation as
  protostomes diversified
• Acoelomate species arose again
• Pseudocoelom, arose independently in certain
  protostome groups.
• Most protostomes have bodies with a basic
  tube-within-a-tube design
• arthropods and mollusks have specialized body
  plans where the coelom is drastically reduced

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Tube- Within-A-Tube
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• Arthropods and mulluscs have a hemocoel
  (blood-hollow) that provides space for internal
  organs and fluid circulation

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Evaluatin Protostome History

• Two major events occurred in the fossil record of
  protostomes
• Extinction of the trilobites, a marine arthropod,
  about 250 million years ago,
• The appearance of insects about 400 million
  years ago

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Evaluating Molecular Phylogenies

• Molecular phylogenies support the hypothesis
  that protostomes are a monophyletic group that
  diverged into two major subgoups.

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What Themes Occur in the Diversification of
Protostomes?
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Protostome Diversification

• Phylogenetic analyses suggests that repeated
  water-to-land transitions occurred as protostomes
  diversified
• Two of the most important problems that animals
  had to solve were
• exchanging gases
• drying out

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Protostome Diversification

• Protostomes solved these problem in different
  ways
• The evolution of specialized body plans provided
  a foundation for diversification in the most
  species-rich lineages
• The arthropods and mollusks

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Feeding

• A wide diversity of feeding strategies is
  reflected in the diversity of mouthparts found in
  protostome animals

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Movement

• Variation in movement depends on
• The presence or absence of limbs and
• the type of skeleton that is present
• Several evolutionary innovations allowed
  protostomes to move in unique ways

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Jointed Limbs

1. Jointed limbs allow for precise swimming and
   running movements

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Wings

1. Insects were the first organisms that had wings
   and could fly

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Muscular Foot

1. The muscular foot allowed mollusks to glide along
   surfaces

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Water Propulsion

1. The muscle-lined mantle allowed the squid to use
   jet propulsion to propel itself backward

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Reproduction and Life Cycles

• Can reproduce asexually via parthenogenesis
• Unfertilized eggs that develop into offspring
• Commonly reproduce via sexual reproduction
• Two innovations occurred during protostome
  diversification (1) evolution of metamorphosis
  and (2) an egg that would not dry out on land.

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Key Lineages of Protostomes
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Lophotrochozoans

• Named for two distinctive morphological traits
  (1) a feeding structure called a lophophore and
  (2) a type of larvae called a trochophore

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Rotifera (Rotifers)

• Rotifers have a corona of cilia at their
  anterior that is used for suspension feeding

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Platyhelminthes (Flatworms)

• This group includes (1) the free-living
  flatworms, (2) the endoparasitic tapeworms, and
  (3) the endo- or ectoparasitic flukes

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Annelida (Segmented Worms)

• Annelids have a segmented body plan and a coelom
  that functions as a hydrostatic skeleton

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Mollusca (Mollusks)

• Most species-rich and morphologically diverse
  group in the Lophotrochozoa.
• Specialized body plan based on a muscular foot, a
  visceral mass, and a mantle that secretes a
  calcium carbonate shell
• Bivalves are suspension feeders
• The other three groups of mollusks are herbivores
  or predators

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MolluscaBivalvia (Clams, Mussels, Scallops,
Oysters)

• The bivalves have two separate shells, made of
  calcium carbonate, that are hinged

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MolluscaGastropoda (Snails, Slugs, Nudibranchs)

• Have a large muscular foot on their ventral side
  and many lack shells

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MolluscaPolyplacophora (Chitons)

• The Greek word roots that inspired the name
  Polyplacophora mean many-plate-bearing
• Have eight calcium carbonate plates along their
  dorsal side

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MolluscaCephalopoda(Squid, Nautilus, Octopuses)

• Have a well-developed head and a foot that is
  modified to form long, muscular tentacles
• They also have large brains and eyes with
  sophisticated lenses.

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Ecdysozoans

• All members of this lineage grow by
  moltingshedding of the exoskeleton or external
  covering (cuticle)

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Nematoda (Roundworms)

• Unsegmented worms with a pseudocoelom
• Tube-within-a-tube body plan
• No appendages
• Common parasites of humans and plants

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Arthropoda (Arthropods)

• Most successful lineage of eukaryotes
• Distinguished by segmented bodies and
  sophisticated exoskeletons
• The body is organized into distinct head and
  trunk regions
• Most species have compound eyes
• Long tentacle-like appendages called antennae

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ArthropodaMyriapods (Millipedes, Centipedes)

• Relatively simple bodies with a series of short
  segments, each with one or two pairs of legs

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ArthropodaChelicerata (Spiders, Ticks, Mites,
Horseshoe Crabs, Daddy Longlegs, Scorpions)
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Chelicerates

• Most are terrestrial
• Includes the arachnids
• Bodies consist of anterior and posterior regions
• Named for appendages called chelicerae found near
  the mouth

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ArthropodaInsecta (Insects)

• Distinguished by having three body regions
  head, thorax, and abdomen
• Three pairs of walking legs on the ventral side
  of the thorax
• In most species, two pairs of wings are mounted
  on the dorsal side of the thorax

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ArthropodaCrustaceans (Shrimp, Lobster, Crabs,
Barnacles, Isopods, Copepods)
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Crustaceans

• Segmented body divided into the cephalothorax and
  the abdomen.
• Many crustaceans have a carapacea platelike
  section of their exoskeleton that covers and
  protects the cephalothorax
• Mouthparts called mandibles that bite or chew.

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