Multicellular and Tissue Level Organization

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Multicellular and Tissue Level Organization

• Chapter 9

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Multicellularity

• Multicellularity
• Multicellular organisms have existed for 550
  million years
• 10 of geological time
• Allowed for a huge population explosion

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Multicellularity

• Hypotheses
• Colonial
• Multicellularity arose as a result of dividing
  cells remaining together, just as colonial
  protists would do.
• Syncytial
• A synctium is a large, multinucleated cell.
• Formation of plasma membranes in the cytoplasm of
  syncytial protist could have produced small,
  multicellular organisms.

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Animal Origins

• The animal kingdom is said to be monophyletic.
• The common ancestor was most likely an ancient
  protist called choanoflagellates
• There is also evidence from molecular studies
  that supports this hypothesis.

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Phylum Porifera

• Phylum Porifera
• Sponges
• Characteristics
• 9000 Species
• Consist of loosely organized cells.
• Range in size from less than a centimeter to more
  than an armful.
• Mostly marine

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Phylum Porifera

• Asymmetrical or superficially radially
  symmetrical
• Three cell types
• Pinacocytes
• Mesenchyme cells
• choanocytes
• Central cavity or branched chambers for filter
  feeding
• No tissues or organs
• Specialized cells
• Spicules
• Skeleton that is made of needle-like spikes
• Skeleton may also be made of calcium carbonate or
  spongin

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Phylum Porifera

• Three cell types
• Pinacocytes
• Thin, flat cells
• Line the outer surface of the sponge
• Mesenchyme cells
• Amoeboid cells that move through mesohyl
• Specialized cells
• Choanocytes or Collar cells
• Flagellated cells
• Line the inner surface of the sponge

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Phylum Porifera

• Water currents
• Ascon or vaselike sponges the simplest and
  least common of the body types.
• Ostia
• Pores that draw water into the sponge
• Spongocoel
• Chamber or tube in the center of the sponge
• Osculum
• Water outlet usually at the top of the sponge

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Phylum Porifera
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Phylum Porifera

• Sycon or folded body sponges
• Dermal pores
• Water enters these pores and leads to a series
  of canals
• Incurrent canal
• Outside of the fold where water enters the
  sponge
• Radial canals
• Choanocytes line these canals

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Phylum Porifera
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Phylum Porifera

• Leucon or sponges extensively branched canal
• Water enters through incurrent canals
• Canals lead to choanocyte lined chambers
• Water leaves the chamber through excurrent canals

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Phylum Porifera
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Phylum Porifera

• Maintenance functions
• Nutrition
• Filter feeder
• 0.1 to 50 µm
• A single leucon sponge 1 cm by 10 cm filters 20
  liters a day

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Phylum Porifera

• Reproduction
• Monoecious
• Both sexes occur in one individual
• Fertilization
• Occurs in the ocean water
• Gemmules
• Asexual reproductive resistant capsules
• Regeneration
• The ability to grow a new individual from a
  piece of the original

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Phylum Porifera

• Class Calcerea
• Characteristics
• Spicules of CaCO3
• Needle shaped with 3 or 4 rays
• Ascon, Leucon or sycon body forms
• All marine
• Calcareous sponges

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Phylum Porifera

• Class Hexactinellida
• Characteristics
• Spicules of silica
• Intricate lattice, 6 rayed
• Leucon or sycon body forms
• 450 to 900 m deep in Pacific ocean
• Glass sponges

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Phylum Porifera

• Class Demospongiae
• Characteristics
• Brilliant colored
• Needle-shaped or four-rayed siliceous spicules
  or Spongin
• Leucon body form
• 1 meter in height
• Freshwater sponges and bath sponges

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Phylum Cnidaria

• Phylum Cnidarian
• Characteristics
• Mostly marine
• Radial or biradial symmetry
• Diploblastic, tissue-level organization
• Gelatinous mesoglea between the epidermal and
  gastrodermal layers
• Gastrovascular cavity
• Nervous system in the form of a nerve net
• Specialized cells, called cnidocytes used in
  defense, feeding, and attachment.

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Phylum Cnidaria

• Body wall and nematocysts
• Diplobalstic
• Epidermis
• Outside layer
• Came from ectoderm
• Gastrodermis
• Inside layer
• Came from endoderm
• Mesoglea
• Jellylike layer between the two cell layers

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Phylum Cnidaria

• Gastrovascular cavity
• Nerve net nervous system
• Cnidocytes
• Stinging tentacle used for defense, feeding, or
  attachment

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Phylum Cnidaria

• Cnidocytes
• Epidermal or gastrodermal cells that produce
  cnidae
• Cnida
• A fluid filled intracellular capsule
• 30 different kinds
• Nematocysts
• Type of cnida with a long tube with spines or
  sticky ends

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Phylum Cnidaria

• Alternation of generations
• Polyp
• Asexual
• Sessile
• Oral end faces up and the aboral end attaches to
  a substrate.
• Anemone
• Medusa
• Dioecious
• Free swimming
• Oral end faces down
• Jelly

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Phylum Cnidaria
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Phylum Cnidaria

• Maintenance functions
• Gastrovascular cavity
• Blind ending
• Functions
• Reproduction
• Food digestion
• Food waste

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Phylum Cnidaria

• Hydrostatic skeleton
• Water or body fluids confined in a body cavity
  where contractile elements of the body wall act

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Phylum Cnidaria

• Movement
• Polyp
• End over end
• Inching along the substrate
• Medusa
• Swimming
• Floating

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Phylum Cnidaria

• Reproduction
• Dioecious
• Polyp
• Planula
• Embryo ciliated, free-swimming larva
• Budding
• Medusa
• Budding

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Phylum Cnidaria

• Class Hydrozoa
• Small
• Mostly marine
• This is the only class in the phylum with
  freshwater species
• Most species display alternation of generations

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Phylum Cnidaria

• Features that distinguish Hydozoans from other
  Cnidarians
• Nematocysts are only found in the epidermis
• Gametes are epidermal and released outside of the
  body
• Mesoglea is largely acellular

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Phylum Cnidaria

• Polyp Hydrozoa
• Mostly colonial polyps
• Obelia common marine cnidarian
• Planula develops a feeding polyp called a
  gastrozooid
• Another reproductive polyp that produces medusa
  is called a gonozooid
• Polyps reproduce asexually
• Medusa reproduce sexually

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Phylum Cnidaria

• Gonionemus
• Medusa stage is dominant
• Velum or shelf-like lip around the edge of the
  medusa
• The velum is only found in Hydrozoa
• Creates a small outlet of water for jet
  propulsion
• Nerve net and nerve ring
• Statocyst sensory structures that orient the
  medusa while swimming

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Phylum Cnideria

• Hydra is the freshwater hydrozoan.
• Hangs from the undersurface of plants.
• Lacks a medusa stage
• Reproduces sexually and asexually

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Phylum Cnidaria

• Class Scyphozoa
• True jellyfish
• Bell diameter 2 meters
• Tentacles length 60 70 meters
• Always in the medusae stage
• Only marine
• Dioecious

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Phylum Cnidaria

• Aurelia
• Feeds on plankton
• Cyanea
• Mastigias quinquecirrha
• Stinging nettle
• Avoid helmet shaped jellyfish

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Phylum Cnidaria

• Class Cubozoa - the amazing box jellies with
  complex eyes and potent toxins
• Approximately 20 species
• both polyp and medsae stages
• resembles the jelly fish with a box shape

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Phylum Cnidaria

• More characteristics
• marine and freshwater
• grow to be about the size of the human head
• 3 meter tentacles
• one tentacle on each of the four corners
• Chironex fleckeri can kill humans

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Phylum Cnidaria

• Class Anthozoa - which includes true corals,
  anemones, and sea pens
• Marine only
• Only polyp stage
• 1 meter of coral reef takes 1000 years to build
• Great barrier reef is 1600 kilometers long

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Phylum Ctenophora

• Phylum Ctenophora
• Form and Function
• fewer than 100 species
• biradial symmetry
• do not sting
• contain colloblasts

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Phylum Ctenophora

• 3 tissue layers
• two tentacles
• complete digestive system
• luminescence common
• triploblastic

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Phylum Ctenophora

• Class Tentaculata
• Contain tentacles
• Tentacle can be retracted
• Class Nuda
• No tentacles