Chapter 9 Multicellular and tissue
organization
Figure 9.1
Physalia physalis
Portuguese Man-of-War
Figure 9.2
•
I. Intro - Origins of
Multicellularity
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Multicellular life has been on earth
for 550 million years, only ~10%
of earth’s 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
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)
Figure 9.3
Two hypotheses regarding the origin of Multicellularity
• II. Phylum Porifera - Sponges
– Primarily marine animals that consist of loosely
organized cells; approx 9k spp, from < 1cm to > 1m
Figure 9.4 (a)
Verongia
Figure 9.4 (b)
Axiomella
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
B. Cell types, Body wall, and Skeletons
1. sponge cells are
specialized for
particular functions
(division of labor)
i.
Pinacocytes
ii. Mesenchyme
iii. Choanocytes
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)
Figure 9.5
Morphology of a Simple Sponge
C. Sponges are supported by skeleton that
may consist of spicules - needlelike spikes.
1. spicules are formed by amoeboid
cells
2. 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
Figure 9.6
Sponge Spicules
D. Water currents and body forms sponges lives depend on the water currents
that choanocytes create
1. water brings food and O2, removes wastes
2. methods of food filtration and circulation reflect body
forms in the phylum. 3 types: (fig. 9.7)
i. Ascon body form
ii. Sycon body form
iii. Leucon body form
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
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.
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 canals
3. proliferation of chambers and canals has resulted in absence of
spongocoel. Often there are multiple exit points for water leaving
sponge
Figure 9.7
• Maintenance functions
• 1, sponges feed on particles that range in size from .1 to
50 um.
– a. bacteria
b. microscopic algae
c. protists
d. other suspended particles
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
.
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 vacuole
d. 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
• 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 sperm
2. other choanocytes may undergo meiosis and form
eggs. Eggs retained in mesohyl of parent
• 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)
Figure 9.8 (abc)
Flagellated cells cover
outer surface
Development of
Sponge Larval
Stages
choanocytes
pinacocytes
• 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 directions
1. there are > 9k spp of Cnidarians, most are marine.
Many important in coral reef ecosystems
Figure 9.9
• 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 net
f. specialized cells called cnidocytes used in defense,
feeding, and attachment
• 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
• 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.
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 attachment
d. some have sticky secretions to anchor itself. 6 or more types
of nematocysts may be found on one individual
Figure 9.10
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
Figure 9.11
Generalized Cnidarian Life Cycle
• 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.
• 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 Obelia
3. 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
Figure 9.12
Figure 9.13 (a)
Figure 9.13 (b)
Figure 9.14 (a)
G. Class Scyphozoa
- true jellyfish dominant life stage is
medusa; cnidocytes
in epidermis and
gastrodermis layer
a) Mastigias
b) Aurelia
Figure 9.15
Figure 9.16
urelia life history (dioecious)
Figure 9.17
ass
Cubozoa- Sea wasp
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
Figure 9.19
Class Anthozoastructure of an
Anemone
Figure 9.20
Class Anthozoa
Figure 9.21 (a)
Other anthozoanOctacorallian coral
(Fleshy sea pen)
Figure 9.21 (b)
Octacorallian Coral- (Purple sea fan)
Figure 9.22 (a)
Phylum Ctenophora- Mnemiopsis known for the bioluminescence
Figure 9.22 (b)
Box Figure 9.1
Coral reef Ecosystem
Box Figure 9.3
Coral Bleeching
Figure 9.23
Cladogram showing Cnidarian Taxonomy
EOC Figure