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Chapter 9
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Chapter 9
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Figure 9.1
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Phyla
• Porifera – (Parazoans)
• Cnidaria – (Eumatozoans)
• Ctenophora – (Eumatozoans)
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Origins of Multicellular Life
• Been around for about 600 million years
• Only 10% of Earth’s geological history
• Appeared about 100 million years
before the Precambrian/Cambrian
boundary (evolutionary explosion)
• All life we know of now + 15-20 extinct
animal groups
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Colonial Hypothesis
• A hypothesis that states that
multicellularity could have arisen as
divinding cells remained together, in the
fashion of many colonial protists.
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Synctial Hypothesis
• A synctium is a large, multinucleate cell.
• The formation of plasma membranes in
the cytoplasm of a synctial protist could
have produced a small, multicellular
organism.
• Also, supported by formations found
within the Protist kingdom.
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Animal Origins
• Animalia is thought to be monophyletic.
• The likely ancestral group has been
identified as the protist group, the
Choanoflagellates.
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Figure 9.2
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Figure 9.3
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Phylum Porifera
• Primarily marine animals consisting of
loosely organized cells
• About 9000 species
• Vary in size from less than a centimeter
to mass that would more than fill your
arms
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Figure 9.4 (a)
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Figure 9.4 (b)
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Characteristics of the Phylum:
• Asymmetrical or superficially radially
symmetrical
• Three cell types: pinacocytes,
mesenchyme cells, and choanocytes
• Central cavity, or a series of branching
chambers, through which water
circulates during filter feeding
• No tissues or organs
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Phylum Porifera
• Class Calcarea – spicules composed of
calcium carbonate; spicules are needle
shaped or have 3 or 4 rays; ascon, leucon, or
sycon body forms; all marine. Calcareous
sponges.
• Class Hexactinellida – Spicules composed of
silica and 6-rayed; spicules often fused in an
intricate lattice; cup or vase shaped; sycon or
leucon body form; found at 450 to 900m
depths in tropical West Indies and Eastern
Pacific. Glass sponges.
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Phylum Porifera (cont.)
• Class Desmospongiae – Brilliantly
colored sponges with needle-shaped of
four-rayed siliceous spicules or spongin
or both; leucon body form; up to 1 m in
height and diameter. Includes 1 family
of freshwater sponges, Spongilladae,
and the bath sponges.
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Cell Types, Body Wall, and Skeletons
• Pinacocytes – thin, flat cells that line
the outer surface of a sponge; may be
contractile vacuole; and their
contraction may change the shape of
some sponges.
• Porocytes – specialized pinacocytes that
can regulate water circulation
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Cell Types, Body Wall, and Skeletons
(cont.)
• Mesohyl – jellylike layer found just
below pinatocyte layer
• Mesenchyme cells – amoeboid cells that
move about in the mesohyl and are
specialized for reproduction, secreting
skeletal elements, transporting and
storing food, and forming contractile
rings around openings in the sponge
wall.
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Cell Types, Body Wall, and Skeletons
(cont.)
• Choanocytes – collar cells, found below
the meshyl and line the inner
chamber(s); flagellated; the flagellum
moves in a circular motion that creates
a water current that moves through the
sponge.
• Spicules – formed by amoeboid cells,
made of calcium carbonate or silica
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Figure 9.5
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Figure 9.6
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Water Currents and Body Forms
• 3 Sponge Body Forms
– Ascon
– Sycon
– Leucon
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Ascon
• Simplest; least common; vaselike; Ostia
are the outer openings of porocytes and
lead directly to a chamber called the
spongocoel; Water exits the sponge
through the osculum (a single large
opening at the top of the sponge.)
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Sycon
• Sponge body wall appears folded; folds
into the sponge are called incurrent
canals; folds out of the sponge are
called radial canals; water enters
through dermal pores; into the
spongocoel and out the osculum
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Leucon
• Have extensively branched canal
system; water enters the sponge
through ostia, through branched
incurrent canals, into choanocyte-lined
chamber, into excurrent canals and
eventually through oscula (multiple
osculum)
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Figure 9.7
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Maintenance Functions
• Feed on particles that range in size from 0.1
to 50 micrometers.
• Food consists of bacteria, microscopic algae,
protists and other suspended organic matter.
• Sponges do not have nerve cells to coordinate body functions. Therefore most
reactions are the result of a single cell
responding to a stimulus.
• Communication between cells may be
possible, but we do not know for certain.
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Reproduction
• Both sponges are monoecious (both
sexes occur in the same individual)
• They do not usually self-fertilize
because they produce sperm and eggs
at different times
• Both the sperm and the egg are formed
by choanocytes that undergo meiosis;
released through the oscula
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Reproduction (cont.)
• Fertilization occurs in the ocean water and
planktonic larvae develop.
• After about 2 days the larvae will settle into
the substrate and begin to develop into the
adult body form.
• Some sponges can reproduce asexually by
producing gemmules that can withstand
harsh temperatures and drought in order to
survive.
• Some sponges have shown that small
portions removed from a larger sponge can
grow into new individuals.
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Figure 9.8 (abc)
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Phylum Cnidaria (ni-dar’ e-ah)
•
•
•
•
9000 species
Mostly marine
Important in coral reef systems
Radially symmetrical animals have no
anterior or posterior regions; thus terms
of direction are based on the placement
of the mouth.
• Mouth end; oral
• Non-mouth end; aboral
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Characteristics of the Phylum Cnidaria
• Radial symmetry or modified biradial
symmetry
• Diploblastic, tissue level of organization
• Gelatinous mesoglea between the epidermal
and gastrodermal tissue 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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The Body Wall
• Diploblastic
– Ectoderm becomes epidermis
– Endoderm becomes gastrodermis
• Tissue-level organization
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Figure 9.9
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Cnidocytes
• Cnidocytes produce cells called cnida
– Cnida are fluid-filled, intracellular capsule
enclosing a coiled, hollow tube
– A lid-like operculum caps the capsule at
one end
– The cnidocyte has a modified cilium called
a cnidocil
– Stimulation of the cnidocil forces open the
operculum, discharging the coiled tube
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Cnida & Nematocysts
• 30 kinds of cnida
• Nematocysts are a type of cnida used for
food gathering and defense that may
discharge a long tube armed with spines that
penetrates the prey (the spines carry a
paralyzing toxin)
• Some cnida contain unarmed tubes that wrap
around prey
• Others produce a sticky substance to help
anchor the animal
• Can be up to 6 different types of cnida on a
single individual
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Figure 9.10
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Alternation of Generations
• 2 body forms
– Polyp – asexual and sessile; attaches to the
substrate at the aboral end; has a
cylindrical body, called a column, and a
mouth surrounded by food gathering
tentacles
– Medusa – diecious and free swimming;
shaped like an inverted bowl, with
tentacles dangling from its margins; mouth
opening is centrally located facing
downward; swims by gentle pulsations of
the body wall
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Figure 9.11
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Maintenance Functions
• The gastrodermis lines the
gastrovascular cavity
– Functions in:
• Digestion
• Exchange of respiratory gases and wastes
• Discharge of gametes
– Food, digestive wastes, and reproductive
stages enter and leave the GC through the
mouth
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Reproduction
• Most are diecious
• Sperm and eggs are released into the
GC or to the outside of the body
• Embryo forms a free-swimming larvae
called a planula
• The planula attaches to the substrate
and a young polyp develops
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Class Hydrozoa
• Small, relatively common
• Mostly marine, 1 class with freshwater
species
• Most display alternation of generations
– In some medusa stage is lost
– In some the polyp stage is very small
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Class Hydrozoa
• 3 features distinguish hydrozoans from
other cnidarians:
– Nematocysts are only in the epidermis
– Gametes are epidermal and released to the
outside of the body rather than into the
gastrovascular cavity
– The mesoglea is largely acellular
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Class Hydrozoa
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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)
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Figure 9.14 (b)
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Figure 9.15
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Figure 9.16
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Figure 9.17
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Figure 9.18 (a)
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Figure 9.19
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Figure 9.20
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Figure 9.21 (a)
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Figure 9.21 (b)
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Figure 9.22 (a)
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Figure 9.22 (b)
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Box Figure 9.1
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Box Figure 9.2
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Box Figure 9.3
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Figure 9.23
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EOC Figure
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