AN INTRODUCTION TO ANIMAL EVOLUTION ECDYSOZOA Bilateral

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ANIMAL EVOLUTION

• AN INTRODUCTION TO

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ECDYSOZOA

• Bilateral animals are divided into two clades
• Protostomes
• Deuterostomes
• Protostomes are themselves divided into two
  clades
• Lophotrochozoa
• Ecdysozoa

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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• Roundworms
• 90,000 known species
• Nonsegmented
• Pseudocoelomates
• Found in various habitats
• Most aquatic habitats
• Wet soil
• Moist plant tissue
• Animal body fluids tissues

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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• lt1 millimeter to gt1 meter in length
• Taper to fine tip at posterior end
• Blunt tip at anterior end
• Covered by cuticle
• Tough exoskeleton
• Periodically shed
• Molting or ecdysis
• Lack a circulatory system
• Nutrient transport via fluid in pseudocoelom

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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• Reproduction generally sexual
• Sexes are separate in most species
• Some are hermaphrodites
• Internal fertilization
• 100,000 or more fertilized eggs can be produced
  by one female per day
• Zygotes resistant to harsh conditions

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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• Important in decomposition nutrient cycling
• Terrestrial and aquatic
• Some are important agricultural pests
• Attack plant roots
• Some are animal parasites
• gt50 species infect humans
• Various hookworms, pinworms, etc.
• e.g., Trichinella spiralis ? trichinosis

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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• Trichinella spiralis
• Causative agent of trichinosis
• Encysted juvenile worms eaten
• Undercooked infected meat
• Juveniles develop into sexually mature adults in
  human intestine
• Females burrow into intestinal muscles
• Produce more juveniles
• Bore through body or travel through lymph system
• Encyst in body organs, including skeletal muscles

Encysted juveniles in human muscle tissue
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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• Caenorhabitis elegans
• Soil nematode approximately 1 mm long
• Model developmental biology research organism
• Simple transparent body
• Most individuals are hermaphrodites
• Self-fertilization quickly uncovers recessive
  mutations
• Some are only male
• Cross-fertilization is possible
• Genome has been sequenced

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ECDYSOZOA

• Ecdysozoa Phylum Nematoda
• Caenorhabitis elegans
• Model developmental biology research organism
• Few cell types
• Exactly 959 cell in adult hermaphrodite
• Cells arise from zygote in virtually the same
  way in all individuals
• Ancestry of all cells can be reconstructed
• Cell lineage
• Fate map

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ECDYSOZOA

• Arthropods
• e.g., Crustaceans, spiders, insects
• Over half of the known species are arthropods
• 1018 (billion billion) individuals in the world

Parasitic mites
Horseshoe crabs
Scorpion
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ECDYSOZOA

• Arthropods
• Coelomate
• Segmented with jointed appendages
• Groups of segments have become specialized for a
  variety of functions
• e.g., Appendages variously modified for walking,
  feeding, sensory reception, copulation, and
  defense
• Important in evolutionary diversification

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Tail fan
Fifth walking leg
Second walking leg
Third maxilliped
Cheliped
Mouth
First antenna
Second antenna
Swimmerets
First swimmeret (used in copulation)
Excretory pore
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ECDYSOZOA

• Arthropods
• Body is completely covered by a cuticle
• Exoskeleton of protein and chitin
• Relatively impermeable to water
• Important in move to land by some groups
• Thick and hard over some parts of body
• Thin and flexible over parts of body
• Protective
• Provides points for muscle attachment
• Must be periodically shed in order to grow

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ECDYSOZOA

• Arthropods
• Well-developed sensory organs
• Eyes
• Olfactory receptors for smell
• Antennae for touch and smell
• Extensive cephalization
• Most sensory organs concentrated at anterior
  end

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ECDYSOZOA

• Arthropods
• Open circulatory system
• Fluid (hemolymph) propelled by a heart through
  short arteries into sinus spaces surrounding
  tissues and organs
• Hemolymph reenters heart through pores
• Pores are generally valved
• Body sinuses collectively termed hemocoel
• Not part of coelom
• Becomes main body cavity in most adults
• Coelom is reduced

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ECDYSOZOA

• Arthropods
• A variety of organs specialized for gas exchange
  have evolved in arthropods
• Allow diffusion of respiratory gases in spite of
  exoskeleton
• Most aquatic species have gills
• Terrestrial species generally have specialized
  internal surfaces
• e.g., Most insects have branched tracheal systems

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ECDYSOZOA
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ECDYSOZOA
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ECDYSOZOA

• Arthropods
• Arthropods diverged early in their history into
  four main evolutionary lineages
• Supported by fossil record
• Supported by molecular systematics
• Supported by comparative anatomy
• Four lineages historically classified into a
  single phylum (Phylum Arthropoda)
• Now classified into four phyla

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ECDYSOZOA

• Arthropods
• Four lineages
• Trilobites (Phylum Trilobita)
• All extinct
• Chelicerates (Phylum Chelicerata)
• Horseshoe crabs, scorpions, ticks, spiders, etc.
• Uniramians (Phylum Uniramia)
• Centipedes, millipedes, and insects
• Crustaceans (Phylum Crustacea)
• Crabs, lobsters, shrimps, barnacles, etc.

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ECDYSOZOA

• Arthropods Phylum Trilobita
• Common inhabitants of shallow Paleozoic seas
• Disappeared 250 million years ago in great
  Permian extinctions
• Pronounced segmentation
• Appendages show little variation from segment to
  segment

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Anterior cephalothorax
• Posterior abdomen
• Appendages more specialized than trilobites
• The most anterior appendages modified as
  chelicerae
• Pincers or fangs

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Most marine chelicerates are extinct
• e.g., Eurypterids (water scorpions)
• Four marine species survive
• e.g., Horseshoe crab

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Class Arachnida
• Includes majority of modern chelicerates
• e.g., Scorpions, spiders, ticks, mites
• Terrestrial
• Six pairs of appendages on cephalothorax
• Chelicerae
• Pedipalps
• Sensing and feeding
• Four pairs of legs

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Class Arachnida
• Ticks and many mites are parasitic
• Most ticks are blood-sucking parasites on body
  surfaces of reptiles, birds, or mammals
• Parasitic mites live on or in a wide variety of
  vertebrates and invertebrates
• Including other arthropods

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Class Arachnida Spiders
• Fanglike chelicerae equipped with poison glands
• Used to attack prey
• Used to masticate (chew) prey
• Spilled digestive juices soften tissues
• Spider sucks up liquid meal

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Class Arachnida Spiders
• In most spiders, gas exchange is carried out by
  book lungs
• Stacked plates contained in internal chamber
• Extensive surface area

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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Class Arachnida Spiders
• Many spiders can make webs
• Used to catch flying insects
• Silk protein produced as a liquid by special
  abdominal glands
• Spun into fibers by organs called spinerettes
• Web style is specific to species

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EXTRUDING SILK
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ECDYSOZOA

• Arthropods Phylum Chelicerata
• Class Arachnida Spiders
• Webs also used as
• Droplines for rapid escape
• Covering for eggs
• Gift wrapping for food males offer females

Latrodectus indistinctus with egg sac
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Diplopoda Millipedes
• Wormlike, with numerous sets of legs
• (Perhaps not nearly one thousand, though)
• Eat decaying leaves and other plant matter
• May have been among the earliest land animals

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Chilopoda Centipedes
• Terrestrial carnivores
• Head has a pair of antenna and three pairs of
  appendages modified as mouthparts
• Each segment of the trunk has a pair of walking
  legs
• Poison claws on anterior-most trunk segment
• Paralyze prey
• Aid in defense

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GIANT PERUVIAN CENTIPEDE
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FLORIDA BLUE CENTIPEDE
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Outnumber all other forms of life combined in
  terms of species diversity
• Live in most terrestrial and freshwater habitats
• Rare (not absent) in seas
• Crustaceans are the dominant arthropods there
• Divided into about 26 orders

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Oldest insect fossils 400 million years old
• Devonian period
• Flight evolved during Carboniferous and Permian
  periods
• Adaptive radiation followed
• Mouthparts indicate specialized feeding on
  gymnosperms and other Carboniferous plants

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Greatest diversification of insects probably
  paralleled the evolutionary radiation of
  flowering plants
• Insect diversification may have been the cause of
  angiosperm radiation, not the effect
• Remember plant/pollinator coevolution?

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Flight is one key to the great success of insects
• Escape predators
• Find food
• Find mates
• Disperse to new habitats

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Many insects have one or two pairs of wings that
  emerge from the dorsal side of the thorax
• Extensions of the cuticle, not true appendages
• No sacrifice of walking legs
• (This is not the case for birds and bats)
• May have originally evolved to help absorb heat
• Other possibilities as well

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Dragonflies were among the first insects to fly
• Two pairs of wings

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Several insect orders that evolved later have
  modified flight equipment
• e.g., Wings of bees wasps hooked together
• Function as a single pair of wings
• e.g., Only the posterior pair of wings function
  in flight in beetles
• Anterior pair of wings are modified as protective
  covers
• Helpful when on the ground or when burrowing

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Several complex organ systems
• Complete digestive system is regionally
  specialized
• Discrete organs function in breakdown of food and
  absorption of nutrients

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Several complex organ systems
• Open circulatory system
• Heart pumps hemolymph through sinuses of hemocoel

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Several complex organ systems
• Metabolic wastes removed from hemolymph by
  excretory organs (Malphigian tubules)
• Outpocketings of digestive tract

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Several complex organ systems
• Gas exchange is accomplished by a tracheal system
• Branched, chitin-lined tubes
• Infiltrate body and carry O2 directly to cells
• Open to the outside of the body through spiracles
• Pores that can open and close to regulate air
  flow and limit water loss

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Several complex organ systems
• Nervous system
• Pair of ventral nerve cords
• Several segmental ganglia
• Cerebral ganglion (brain) near antennae, eyes,
  and other sense organs in head

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Many insects undergo metamorphosis in their
  development
• Incomplete metamorphosis
• Complete metamorphosis

Ecdysis Molting cricket
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Incomplete metamorphosis
• e.g., Grasshoppers
• Young resemble adults
• Smaller with some different body proportions
• Series of molts until full size is reached
• Look more like adult with each molt

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ROACH ECDYSIS
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Complete metamorphosis
• Larval stage specialized for eating and growing
• Maggot, grub, caterpillar, etc.
• Looks entirely different from adult stage
• Metamorphosis from larval stage to adult stage
  occurs during pupal stage

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Growth and molting
adult
young
egg
Incomplete metamorphosis
egg
adult
nymphs
Complete metamorphosis
adult
egg
pupa
larvae
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Reproduction is usually sexual
• Separate male and female individuals
• Mate recognition by
• Bright colors (e.g., butterflies)
• Sound (e.g., crickets)
• Odors (e.g., moths)

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Fertilization is generally internal
• In most species, sperm deposited in vagina during
  copulation
• In some species, male deposits a sperm packet
  outside female
• Sperm stored in organ termed spermatheca
• Usually enough for gt1 batch of eggs
• Eggs laid on suitable food source
• Next generation can begin eating immediately upon
  hatching

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta Drosophila melanogaster
• Model research organism
• Genetics
• Developmental biology

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Drosophila melanogaster
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Insecta
• Very diverse, numerous, and widespread
• Affect the lives of all other terrestrial
  organisms
• e.g., Pollination
• e.g., Vectors for disease-causing microorganisms
• Mosquitoes carry Plasmodium ? malaria
• Tsetse flies carry Trypanosomes ? sleeping
  sickness
• e.g., Competition with humans for food
• Insects claim 75 of crops in some regions of
  Africa

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• Bugs are not going to inherit the Earth. They
  own it now. So we might as well make peace with
  the landlord.

• Thomas Eisner Cornell University

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• 40,000 species currently alive
• e.g., Crabs, lobsters, crayfish, shrimp
• Multiple appendages are extensively specialized
• Two pairs of antennae
• Three or more pairs are modified into mouthparts
• Walking legs on thorax and abdomen
• (19 pairs of appendages in lobsters and crayfish)
• Lost appendages can be regenerated

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CRUSTACEANS
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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Small crustaceans exchange gases across thin
  areas of cuticle
• Larger species possess gills
• Open circulatory system
• Heart pumps hemolymph through arteries into
  sinuses bathing organs
• Excrete nitrogenous waste by diffusion through
  thin areas of cuticle
• Pair of glands regulate salt balance of hemolymph

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Sexes are separate in most crustaceans
• Specialized appendages on male lobsters and
  crayfish transfer sperm to reproductive pore of
  female during copulation
• Most marine species go through one or more
  swimming larval stages

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Various groups
• Isopods
• Copepods
• Decapods

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Isopods
• Mostly small marine species
• Some are numerous on bottoms of deep oceans
• Include some terrestrial species
• Pill bugs (wood lice)

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Copepods
• Among the most numerous of all animals
• Important members of marine and freshwater
  plankton communities
• Eat protists and bacteria
• Eaten by many fishes

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Decapods
• Relatively large crustaceans
• e.g., Lobsters, crayfish, crabs, and shrimp
• Most are marine
• Some live in freshwater (e.g., crayfish)
• Some live on land (e.g., some topical crabs)
• Cuticle (exoskeleton) hardened by calcium
  carbonate
• Portion covering dorsal side of cephalothorax
  forms protective shield
• Carapace

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Larvae of many larger crustaceans are also
  planktonic
• e.g., Krill
• Up to 3 cm long
• Major food source for many species of whales
• Now being harvested as human food source

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ECDYSOZOA

• Arthropods Phylum Uniramia
• Class Crustacea
• Barnacles are sessile crustaceans
• Parts of cuticles hardened into shells by calcium
  carbonate
• Feed using appendages to strain food from water

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SEGMENTATION

• Many groups display segmentation
• e.g., Annelids, arthropods, vertebrates, etc.
• Segmentation likely evolved multiple times
  independently
• Segmentation involves two sets of genes
• Segmentation genes
• Hox genes
• We will discuss this in more detail later

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DEUTEROSTOMIA

• Bilateral animals are divided into two clades
• Protostomes
• Deuterostomes
• Protostomes are themselves divided into two
  clades
• Lophotrochozoa
• Ecdysozoa

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Superficially appear to display radial symmetry
• Larvae have bilateral symmetry
• Radial anatomy of adult is secondary adaptation
• Adults are not truly radial in their anatomy
• e.g., Opening of water system is set to one side,
  not central

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Sessile or slow-moving animals
• e.g., Sea stars, sea urchins, sea cucumber, etc.
• Parts of animal radiate from center
• Often five spokes
• Thin skin covers endoskeleton of hard calcareous
  plates
• Most are prickly from skeletal bumps and spines
  of various functions

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ECHINODERMS
Sea star
Brittle star
Sea lily
Sea urchin
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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Water vascular system
• Unique to echinoderms
• Network of hydraulic canals branching into
  extensions
• Tube feet
• Function in locomotion, feeding, gas exchange

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Sexual reproduction generally involves separate
  male and female individuals releasing their
  gametes into the seawater
• Radial adult develop by metamorphosis from
  bilateral larvae

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• 7,000 living species
• All are marine
• Divided into six classes
• Asteroidea (sea stars)
• Ophiuroidea (brittle stars)
• Echinoidea (sea urchins sand dollars)
• Crinoidea (sea lilies feather stars)
• Holothuroidea (sea cucumbers)
• Concentricycloidea (sea daisies)

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Class Asteroidea (Sea stars)
• Five arms radiate from a central disk
• Capable of regeneration of lost arms
• Undersurfaces of arms bear tube feet
• Act as suction disks
• Used to move
• Used to grasp prey such as bivalves
• Everts stomach through mouth into opening between
  bivalve shell
• Digestive juices begin digesting mollusk within
  its own shell

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Class Ophiuroidea (brittle stars)
• Distinct central disks
• Arms are long and flexible
• Tube feet lack suckers
• Movement by serpentine lashing of the arms
• Some are suspension feeders
• Some are scavengers

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Class Echinoidea (sea urchins sand dollars)
• Possess five rows of tube feet, but no arms
• Function in slow movement
• Sea urchins also possess muscles that pivot long
  spines
• Also aid in movement
• Urchin mouth ringed by jawlike structures
• Adapted to eating seaweeds, etc.

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Class Crinoidea (sea lilies feather stars)
• Ancient lineage has changed little in 500 million
  years
• Arms encircle upward-directed mouth
• Used in suspension feeding
• Sea lilies live attached to substratum by stalks
• Feather stars crawl around using long, flexible
  arms

Sea lily
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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Class Holothuroidea (sea cucumbers)
• Lack spines
• Hard endoskeleton is reduced
• Elongated in oral-aboral axis
• Five rows of tube feet
• Some tube feet around mouth are developed as
  feeding tentacles

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DEUTEROSTOMIA

• Deuterostomia Phylum Echinodermata
• Class Concentricycloidea (sea daisies)
• Recently discovered
• Live on waterlogged wood in deep sea

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DEUTEROSTOMIA

• Deuterostomia Phylum Chordata
• Two invertebrate subphyla
• Subphylum Vertebrata
• Contains all vertebrates
• Chordates and echinoderms have existed as
  distinct phyla for at least 500 million years

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ANIMAL PHYLOGENY
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ANIMAL PHYLOGENY