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Phylum: Porifera
Phylum: Porifera
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~ 10,000 described species
mainly marine
a few freshwater species, including
some locally in streams. Sessile. Asymmetric body plan
–  2 cell layers: diploblastic
–  surrounding a central cavity
Water flows into this central
cavity through numerous small
pores. Choanocytes
Oscula (or 1 osculum)
Spicules
Chemical defenses
No real tissues
Osculum
Spicules
Choanocyte
Body Symmetry, Body Plans
•  Radial or Bilateral Symmetry
•  Coelomate or acoelomate
•  Protostome or deuterostome
Phylum: Cnidaria
•  Uncephalized
–  Nerve net is present
–  No brain
•  Radial symmetry
•  Anterior/posterior axis
–  Developmental gene expression gradients
–  ~ 10,000 described species •  Hydras, sea anemones, jellyfish, corals. •  Body plan
–  2 layers after gastrulation: ectoderm and endoderm . •  Body forms: medusa (jellyfish) and polyp (others).
Mesoglea (jelly)
polyp
Gastrodermis (endoderm)
Epidermis (ectoderm)
medusa
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Cnidaria: Hydra
•  Nematocysts
•  present in all cnidaria
•  specialized capsules within epidermal cells
•  shoot out stinging barbs
•  paralyze prey
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Hydras –  common in freshwater –  eat primarily small crustaceans •  (e.g., Daphnia). –  Cnidarians are uncephalized
•  No brain
•  nervous network –  Sensory
–  Controls movements. •  Movement
–  by specialized contracting cells Sea anemones
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Often large and colourful
“Swim” away from predators, Do battle with each other. Stings are not toxic to us. Tentacles will pull on fingers Jellyfish
mouth
epidermis
mesoglea
tentacle
interacting
cells of
nerve net
gastrodermis
sheet of epidermal cells
with contractile properties
•  Common marine animals •  Range from tiny to huge. • Trail long tentacles •  lined with nematocysts •  Medusa pulses • creates currents •  pulls food into tentacles.
Below: Box jelly is dangerous even to humans
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Colonial Cnidarians: Portuguese Man-O-War
Several polyps, connected to a float with a “sail”. They can deliver a
particularly nasty sting when the tentacles wrap around your legs.
gas-filled
float
reproductive polyp
Colonial Cnidarians: Corals
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Calcified chambers form the great coral reefs surrounding oceanic islands. Atolls result from complete erosion of the original island. Protistan symbionts contribute much of the energy
“Bleaching” occurs when symbionts die -- –  High ocean temperatures –  Pollutants (e.g., phosphates)
feeding polyp
polyp
‘team’
stinging, prey
-captured polyp
Cnidaria reproduce both sexually, via sperm/eggs, zygotes, and planula
larvae, or asexually by budding off a new polyp or medusa.
reproductive polyp
male medusa
female medusa
Ctenophora: Comb Jellies
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ovum
sperm
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zygote
feeding
polyp
Resemblances to Cnidaria
–  Jelly-like mesoglea assist in flotation
Differences –  Generally smaller
–  more fragile, –  rarer, –  entirely marine,
–  never sessile. Formal differences
–  Swim by the beating of eight rows of combs,
or fused cilia, –  No nematocysts. –  Form 3rd layer of embryonic tissue
•  Resembles mesoderm of more complex
animals. one branch
from a
mature
colony
branching
polyp
forming
planula
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Phyla •  Acoelomate/Radial symmetry
–  *Placozoa –  *Porifera –  *Cnidaria –  *Ctenophora •  Acoelomate/Bilateria
–  Platyhelminthes
–  Nemertea
–  Nematoda
–  Rotifera?
•  Coelomates
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Rotifera?
Molluscs
Annelids
Onychophora
Arthropods
Echinoderms
Chordates
•  Vertebrates
–  Agnatha
–  Placodermi
–  Chondrichthyes
–  Osteichthyes
–  Amphibia
–  Reptilia
–  Aves
–  Mammalia
»  Prototheria or monotremes
»  Metatheria or marsupials
»  Eutheria (placental
mammals)
Arthropods
mouth
coelom
segmented
body
Annelids
Mollusks
head
Roundworms
anus
false
coelom
complete
digestive
system
bilateral
symmetry,
cephalization
no coelom
unsegmented
body
Flatworms
Bilateral symmetry
mouth
Radial/Asymmetry
radial
symmetry, no
cephalization
saclike
gut
Cnidarians
Where do acoelomate animals keep their internal organs?
•  So what is a coelom?
–  A body cavity lined by mesoderm.
–  The coelom is not the gut. •  Not ever!
•  Only triploblastic (3-layered) animals
ever have a coelom.
•  Do humans have a coelom?
– Packed into the mesoderm without any cavity.
– Organs are less cushioned.
epidermis
gut
cavity
organs packed between
gut and body wall
Platyhelminthes are acoelomate animals
Fig. 25-4a, p. 405
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Worms
ectoderm
Above Cnidaria, animal phyla are all bilaterally symmetrical, and are
clearly a monophyletic clade. The combined phyla are sometimes
referred to as the Bilateria, which can be considered a superphylum or
subkingdom. mesoderm
endoderm
Radial symmetry
Fig. 25-2, p. 404
Evolutionary Tree of Animals
Bilateral symmetry
Phylum Platyhelminthes
(Flatworms)
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~ 15,000 aquatic & terrestrial species
Mesoderm --
–  Clear layer between ectoderm and endoderm
–  Gives rise to various internal organs •  Excretory system, muscles, nervous system
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–  Still have blind gut
Cephalization
–  Anterior concentration of sensory systems
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Acoelomate
•  Touch, smell, primitive sight
Today’s topic: worms
and an “odd” phylum
*rotifers?
•  No circulatory system
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Platyhelminthes -- Class: Turbellaria (planarians)
Free-living, mostly marine but some freshwater
Eat small animals and decaying flesh
Have an extrudable pharynx that opens into the gut.
Planaria: Reproduction
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brain
nerve cord
ovary
testes
oviduct
genital pore
penis
branching gut
Sexual reproduction
Asexual regeneration
All cells can obtain oxygen from water
by diffusion.
Only 1 opening into body
pharynx (protruded)
protonephridia
Phylum Platyhelminthes: 2. Class Trematoda (Flukes)
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Parasitic worms
Complicated life cycle
–  Larval stage infects a
mollusk –  Adult infects a vertebrate
Genus Schistosoma Worms mate in
human host
–  Causes schistosomiasis
or bilharziasis
•  Chronic infection
damages liver, intestines,
lungs, and bladder
•  Mechanism is body’s
defensive reactions to
Schistosoma eggs
Larvae bore
into human
skin
Larvae form,
leave snail
Sexual reproduction
–  hermaphroditic
Asexual reproduction
–  split in two
–  regenerate symmetrical sides.
•  Amazing capacity for regeneration
–  Studied by scientists
»  E.g., Phillip Newmark in
Cell and Developmental
Biology
»  Goal is to understand
human regenerative
capacities –  Requires stem cells
»  capable of regenerating both
themselves and other more
specialized cells
•  Think about the physical costs of a serious
infestation of worms. •  200 million cases/year, worldwide •  A new drug, praziquantel, is remarkably
effective against the worms
• One dose controls disease for up to five years.
•  This might make it possible to interrupt the
life cycle of the worms.
Fertilized egg
Asexual reproduction
in intermediate host
Ciliated larva
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Phylum Platyhelminthes: 3. Class Cestoda
(Tapeworms)
Phylum Platyhelminthes
3. Tapeworms: Class Cestoda
•  Primarily gut parasites of vertebrates •  Extremely modified and simplified morphology
•  A barbed head and repeated reproductive segments. Definitive host
Larvae
encysted in
muscle
tissue
Larvae form cysts
in muscle tissue
Phylum Nemertea: Ribbonworms
Intermediate
host
Scolex attaches
to host
intestinal wall
Mature proglottid with fertilized eggs
Phylum Nematoda (Roundworms)
(also hookworms, heartworms, trichina)
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Entirely marine: ~ 1000 species known
Prey on other animals using a unique proboscis
Complete gut (unlike flatworms)
Protostome –  Mouth forms from the blastopore –  Anus forms from a secondary invagination near the posterior end
•  Acoelomate
•  Pseudo-coelom forms between the ectoderm and endoderm –  Results in round cross-section
–  contains tissues formed from mesoderm
•  circulatory system.
•  Alternating layers of longitudinal and circular muscles allow
sinusoidal movement.
•  >>20,000 species
•  Small: seriously under-appreciated fauna in most environments. –  Major parasitic problem in plants and animals
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Filariasis: caused by parasitic nematodes
Phylum Nematoda:
Caenorhabditis elegans [C. elegans]
•  Tropical diseases •  Caused by 2 species:
–  Brugia malayi, –  Wucheria bancrofti. •  Transmitted by mosquitos
•  Worms block lymph nodes
–  Leads to massive swelling
•  Elephantiasis
•  Difficult to develop drugs against
these animal parasites
–  Similar physiology, –  Mediated by similar genes,
proteins
•  Now considered eradicable
Phylum Rotifera
•  Small -- 0.1-0.5 mm
•  Free-living
–  Mostly freshwater
–  Some marine
•  Complexity similar to worms
–  Pseudocoelom; complete gut;
protonephridia
–  Nervous system; brain
–  No circulatory system
•  Move by rapidly beating cilia
–  not by muscle contraction
•  Males & females in most species
•  One major lineage appears not to have had
sex for about 100 Myr!
•  DNA evidence suggests relationship to
Lophotrochozoa (eg. annelids, molluscs)
•  Free-living soil nematode
•  Model organism
–  1 mm long
–  959 cells
•  Fully described:
–  Each cell division
–  All developmental cell death
–  All nerve connections
•  Genome sequenced
–  1st animal genome, 1998
–  ~ 100 million base pairs of DNA
–  ~20,000 genes
•  1,500 chemoreceptors
–  = 7.5% of all its genes
/proteins
Phyla •  Acoelomate/Radial symmetry
–  ✔Placozoa
–  ✔Porifera –  ✔Cnidaria
–  ✔Ctenophora
•  Acoelomate/Bilateria
ü  Platyhelminthes
ü  Nemertea
ü  Nematoda
ü  Rotifera
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Coelomates (Bilateria continued)
–  Molluscs
–  Annelids
–  Onychophora
–  Arthropods
–  Echinoderms
–  Chordates
•  Vertebrates
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Remember the mnemonic for Linnaean classification:
King Phillip Came On Foot Gathering Subjects
Agnatha
Placodermi
Chondrichthyes
Osteichthyes
Amphibia
Reptilia
Aves
Mammalia
»  Prototheria or
monotremes
»  Metatheria or marsupials
»  Eutheria or placental
mammals
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