Chapter 9 Multicellular and tissue organization

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Chapter 9 Multicellular and tissue organization
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Figure 9.1
Physalia physalis Portuguese Man-of-War
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Figure 9.2
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• I. Intro - Origins of Multicellularity
• Multicellular life has been on earth for 550
  million years, only 10 of earths geological
  history
• colonial hypothesis multicellularity began as
  dividing cells remained together, as do many
  colonial protests (fig. 9.3)
• syncytial hypothesis multicellularity evolved
  from large, multinucleated cells that developed
  internal plasma membranes
• Both of these happen in different protests

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Are animals polyphyletic or monophyletic? The
nearly simultaneous appearance of all animal
phyla makes it hard to tell

• 1. if animals are polyphyletic, more than one
  explanation of the origins of multicellularity is
  possible

2.  more than one body form could be ancestral

• 3.  however, impressive similarities in animal
  cell organization support monophyletic origin (eg
  asters in cell division, cell junctions are
  similar in all animal cells, most animals produce
  flagellated sperm and most animal cells use
  similar proteins to accomplish movement)

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Figure 9.3
Two hypotheses regarding the origin of
Multicellularity
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• II. Phylum Porifera - Sponges
• Primarily marine animals that consist of loosely
  organized cells approx 9k spp, from lt 1cm to gt
  1m

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Figure 9.4 (a)
Verongia
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Figure 9.4 (b)
Axiomella
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A. Characteristics of members of Phylum Porifera
include

• 1.  asymmetrical or radial symmetry
• 2.  3 types of cells - pinacocytes, mesenchyme
  cells
• (amoebocytes) and choanocytes
• 3.  Central cavity or several branching chambers,
  thru which water flows for filter feeding
• 4.  no tissues or organs

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B. Cell types, Body wall, and Skeletons

• 1.  sponge cells are specialized for particular
  functions (division of labor)
• Pinacocytes
• Mesenchyme
• Choanocytes

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• a. pinacocytes - flat, thin cells that line the
  outer surface of a sponge. Pinacocytes may
  be      slightly contractile and help sponge
  change shape. Some pinacocytes specialized into
  porocytes, which regulate water circulation (fig.
  9.5)

b.  jelly like layer under pinacocytes is termed
mesohyl. Mesenchyme cells are amoeboid, and move
about in the mesohyl. Specialized for
reproduction, transporting and storing food,
secreting skeletal elements (spicules)
c.  beneath mesenchyme, lining inner chambers
are choanocytes - collar cells. Flagellated cells
with ring of microvilli surrounding flagella.
Microfilaments connect microvilli, forming a net
that helps filter edible particles (Fig. 9.5)
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Figure 9.5
Morphology of a Simple Sponge
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C. Sponges are supported by skeleton that may
consist of spicules - needlelike spikes.

• spicules are formed by amoeboid cells
• made of CaCO3 or silica
• 3. may take on a variety of shapes ( fig. 9.6)
• 4. alternatively, skeleton may be made of
  spongin, a fibrous protein made of collagen -
  dried beaten and washed to produce commercial
  sponges

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Figure 9.6
Sponge Spicules
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D.  Water currents and body forms - sponges lives
depend on the water currents that choanocytes
create                                          

• 1.  water brings food and O2, removes wastes
• methods of food filtration and circulation
  reflect body forms in the phylum. 3 types (fig.
  9.7)
• Ascon body form
• Sycon body form
• Leucon body form

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i. ascon body form - simplest and least common.
Vaselike form

• 1. ostia are outer openings of porocytes and lead
  directly to chamber called spongocoel
• 2. choanocytes line spongocoel and their
  flagellar movements draw water into the
  spongocoel thru the ostia
• 3. water exits sponge thru osculum, single large
  opening at the top of the sponge

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• ii. sycon body form - sponge wall appears folded
• 1. water enters thru dermal pores, which are
  openings of incurrent canals
• .pores in body walls open to radial canals, and
  radial canals lead to spongocoel
• .choanocytes line radial canals and beating of
  flagella moves water from ostia, thru incurrent
  and radial canals, to spongocoel and out the
  osculum.

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• iii. leucon body forms have an extensively
  branched canal system.
• 1. Water enters the ostium and moves thru
  branched incurrent canals,
• 2.  incurrent canals lead to choanocyte lined
  chambers. Canals leading away from the chambers
  are called excurrent canals3.  proliferation of
  chambers and canals has resulted in absence of
  spongocoel. Often there are multiple exit points
  for water leaving sponge

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Figure 9.7
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• Maintenance functions
• 1, sponges feed on particles that range in size
  from .1 to 50 um.
• a. bacteriab.  microscopic algaec. 
  protistsd.  other suspended particles

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• 2. important in reducing coastal turbidity
• a. 1 leucon sponge, 1 cm in diameter and 10 cm
  high, filters 20 liters of water/day!
• 3.  a few sponges are carnivorous - catch small
  crustaceans (deep water) with spicule-covered
  filaments
• .

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• 4.  feeding methods - choanocytes filter small
  suspended particles.
• a. Water passes thru collar near base and moves
  into spongocoel at open end of collar
• b. suspended food is trapped on collar and moved
  along microvilli to base of collar, where it is
  incorporated into a food vacuole
• c.  lysozymal enzymes and pH changes digest
  particle in vacuoled.  partly digested food
  passed to amoeboid cells, that distribute it.
• 5.  other feeding methods -
• a. pinacocytes lining incurrent canals may
  phagocytize larger food particles. Sponges may
  also absorb nutrients in sea water thru active
  transport

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• Reproduction - most sponges are monoecious - both
  sexes occur in same individual do not usually
  self fertilize because eggs and sperm ready at
  different times.
• 1. certain choanocytes lose collars and flagella
  and undergo meiosis to form flagellated sperm2. 
  other choanocytes may undergo meiosis and form
  eggs. Eggs retained in mesohyl of parent

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• 3.  sperm cells exit one sponge by osculum and
  enter another with incurrent water. they are
  trapped by choanocytes and put in vacuoles.
• 4.sperm lose collar and flagella, become ameboid
  and transfer sperm to eggs
• 5. early development occurs in mesohyl, then a
  flagellated larva forms. Larva breaks free,
  free-swims for up to 2 days before settling to
  substrate and develops into adult form (Fig. 9.8)

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Figure 9.8 (abc)
Flagellated cells cover outer surface
Development of Sponge Larval Stages
choanocytes
pinacocytes
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• III. Phylum Cnidaria
• A. Intro - Members of Phylum Cnidaria possess
  radial symmetry -advantageous in sedentary
  animals because the sensory receptors are evenly
  distributed around the body - can respond to
  stimuli from all directions1.  there are gt 9k
  spp of Cnidarians, most are marine. Many
  important in coral reef ecosystems

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Figure 9.9
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• 2.  Characteristics include
• a. radial symmetry
• b. diploblastic, tissue level organization
• c. gelatinous mesoglea between epidermal and
  gastrodermal tissue layers
• d.  gastrovascular cavity
• e.  nervous system in form of a netf. 
  specialized cells called cnidocytes used in
  defense, feeding, and attachment

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• B.  Body Wall and nematocysts
• 1. diploblastic tissue organization - cells
  organize into tissues that can carry out more
  complex functions than individual cells all
  cells derived from 2 embryological layers
• 2.  ectoderm of embryo gives rise to epidermis,
  endoderm gives rise to inner layer, called
  gastrodermis
• a. cells differentiate into specialized cells for
  protections, food gathering, coordination,
  movement, digestion, and absorption

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• 3.  between the 2 layers is a jellylike layer
  called the mesoglea cells present in this layer
  come from either epidermis or gastrodermis
• 4.  cnidocytes - cells characteristic of the
  phylum - Epidermal and gastrodermal cells both
  give rise to cnidocytes. Cnidocytes produce
  structures called nematocysts - feeding, defense,
  attachment.

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• 5.  a nematocyst is a fluid filled intracellular
  capsule enclosing a coiled, hollow tube (Fig.
  9.10).
• A lid-like operculum covers capsule at one end.
  The cnidocyte has a modified cilium at the end,
  the trigger. If stimulated, it ejects the coiled
  tube within, like a sweater sleeve turned inside
  out.
• a. cnidocysts may have spines to penetrate prey
• b.  some have toxins that are injected to
  paralyze prey
• c.  others have unarmed tubes that wrap around
  prey or substrate for attachmentd.  some have
  sticky secretions to anchor itself. 6 or more
  types of nematocysts may be found on one
  individual

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Figure 9.10
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• C.  Alternation of Generations - most cnidarians
  possess 2 body forms in their life histories
• 1. polyp - usually asexual and sessile attaches
  to substrate at base, column (cylindrical body
  form) is capped by a mouth surrounded by
  tentacles
• 2. medusa is dioecious and free swimming. shaped
  like inverted bowl, tentacles hang from rim.
  Mouth is centrally located facing downward, and
  medusa swims by pulsating body walls. More
  mesoglea in medusas than in polyps    

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Figure 9.11
Generalized Cnidarian Life Cycle
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• E.  Reproduction - most are dioecious - each has
  a particular gender.
• 1. sperm and eggs are released into gv cavity or
  to the outside. In some cases, eggs stay in mom
  till fertilization embryo enlarges to form a
  ciliated, free swimming larva called a planula.
  Planula attaches to substrate, interior cells
  split to form gastrpvascular cavity and polyp
  develops
• 2. medusae nearly always form from budding from
  body wall of polyp and polyps form other polyps
  by budding. buds may detach, or remain attached
  to contribute to a colony.

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• F.  Class Hydrozoa - hydras - small relatively
  common cnidarians most marine, but some are
  freshwater -characteristics cnidocysts in
  epidermis release sperm and eggs out of body
• 1, most hydrozoans have alternation of
  generations, but in some, medusa stage is lost
  in others, polyp stage is very small
• 2.  most hydrozoans are colonial w/ some
  individuals specialized for feeding and others
  specialized for defense or reproduction e.g
  Obelia3.  Gonionemus has a mostly medusa form,
  living in shallow marine waters.4.  Hydra is a
  freshwater hydrozoan that hangs from underside of
  floating plants in streams and ponds - lacks
  medusa stage

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Figure 9.12
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Figure 9.13 (a)
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Figure 9.13 (b)
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Figure 9.14 (a)
G.  Class Scyphozoa - true jellyfish - dominant
life stage is medusa cnidocytes in epidermis and
gastrodermis layer
a) Mastigias b) Aurelia
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Figure 9.15
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Figure 9.16
Aurelia life history (dioecious)
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Figure 9.17
Class Cubozoa- Sea wasp
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Figure 9.18 (a)
H.  Class Anthozoa - anemones and corals -
colonial or solitary, and lack medusae. Differ
from hydrozoans bc sperm and eggs released into
gastrovascular cavity and expelled from there
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Figure 9.19
Class Anthozoa- structure of an Anemone
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Figure 9.20
Class Anthozoa
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Figure 9.21 (a)
Other anthozoan- Octacorallian coral (Fleshy sea
pen)
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Figure 9.21 (b)
Octacorallian Coral- (Purple sea fan)
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Figure 9.22 (a)
Phylum Ctenophora- Mnemiopsis known for the
bioluminescence
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Figure 9.22 (b)
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Box Figure 9.1
Coral reef Ecosystem
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Box Figure 9.3
Coral Bleeching
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Figure 9.23
Cladogram showing Cnidarian Taxonomy
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EOC Figure