5. General Description
- Ctenophores are major predators upon larval
fish and zooplankton. They may prey on small
crustaceans (phylum Arthropoda) and the
larval stage of various fish and jellyfish
species, and oysters. Some are carnivorous
on other ctenophores or gelatinous animals in
other groups. They play a role in estuarine
ecology.
- Most are nearly transparent
- The 100 or so described species are
exclusively marine and most are planktonic. A
member of most species are weak swimmers,
carried about by ocean current
6. - The ctenophore’s tentacles are solid rather
than hollow
- Ctenophores have left a poor fossil record
- There is an evolutionary relationship between
Ctenophora and Cnidaria.
- Nearly all ctenophores are bioluminescent.
They give off excess energy in the form of
light instead of heat.The functional
significance of bioluminescence includes
mate location and species recognition, luring
of prey, and the startling of would-be
predators.
7. Some species may use bioluminescence to
avoid detection by visual predators, producing
light of ambient intensity. This would break out
the silhouette of the animal when observed by
potential predators from below, helping the
lighted form blend into the surroundings.
9. A. Body Covering
• Its body covering is somewhat
reminiscent of Cnidarian medusae.
• The body consists of an outer
epidermis, an inner gastrodermis, a
thick, middle mesoglea layer.
• It has a basic radial symmetry, with oral
and aboral surfaces.
10.
11. B. Digestive System
• The mouth leads into a pharynx called a
stomodeum, which serves as a site for
extracellular digestion.
• It goes through a stomach into a series
of gastrovascular canals, where
digestion is completed intracellularly.
12. C. Excretory and Respiratory System
• There are no functional Excretory and
Respiratory organs found in
Ctenophores.
14. E. Development Stages
• At lest one ctenophore species has a
planula larval stage in its life history.
• During embryogenesis, Ctenophores
form no distinct mesodermal layer.
Thus, they are termed as dipoblastic.
15. A Comparative Study of Ctenophora
and Cnidaria
Point of Ctenophora Cnidaria
Comparison
1. Body Biradial Radial
symmetry
2. Not Polymorphic
Polymorphism Polymorphic
3. Cells Multiciliated Monociliated
cells cells
16. Ctenophora Cnidaria
4. Genuine Myoephitelial
Smooth muscle cells
Type of musculature
5. Multiciliated Monociliated
Swimming Mechanism
cells cells
6. Tentacles are Tentacles are
Mechanism and studded with capture
mode of food studded with
colloblasts nematocysts
7. 4 digestive One opening
Means of food digestion and waste both mouth
canals and for elimination
anal pores and anus
17. Ctenophora Cnidaria
8. Hermaphroditic Gonochoristic
Nature of Sexuality
9. Gastrulation Gastrulation
Aspects of Embryonic Development
through epiboly through
or invagination delamination
or ingression
18. Types of Musculature
• Ctenophores are tripoblastic. Its muscles
develop from amoeboid cells found with the
mesoglea. Whereas, the muscles of cnidarians
are found within the gastrodermis and, to a
lesser extent, within the epidermis.
• Ctenophores have genuine smooth muscle
tissues and lack the Myoephitelial cells that are
found in Cnidarian musculature.
• The Mnemiopsis leidy and Beroë sp. are the
first known giant smooth muscle fibers,
measuring up to 6 cm long. These are of the
Ctenophore species.
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20. Swimming Mechanism
• Ctenophores swim through the activity of
many bands of partially fused, remarkably
long cilia. The power stroke of each cilia is
towards the aboral surface, so that it swims
mouth first. Cnidarians, however, swim by
means of jet propulsion.
• Back to Table
21.
22. The Ctene
• Each band of Cilia is fused to a ctene (Gk.
Comb) because of its resemblance to a comb.
• The ctene is organized into 8 distinct rows
called costae which extends from the oral to
the aboral surface of the animal.
• The intensity of activity in the different comb
rows is under the control of an apical sense
organ at the aboral end of the ctenophore.
Together with an epidermal nerve, It
synchronizes the coordination of ciliary
beating in different comb rows.
23. • A single sphere of calcium Carbonate, called
statolith, sits atop 4 tufts of fused cilia called
balancers, or springs. Each balancer is
composed of several hundred cilia.
• A ciliated groove radiates from each
balancer and bifurcates to service two other
adjacent rows. These serve as agents of
nerve impulse conduction from the apicak
sense organ to the ctenes of the comb rows.
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24. Mechanism and Mode
of Food capture
• The tentacles of ctenophores can be
completely retracted into proximal pits
or sheaths, unlike that of the cnidarians.
• Its general epidermis are studded with
colloblasts, whereas the tentacles of
cnidarians are surfaced with
nematocysts.
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25. Mode of Food Capture
• Each colloblast cell consists of a bulbous,
sticky head connected to a long, straight
filament. Prey organisms become stuck to the
tentacles which are then retracted. In other
species, the body rotates to bring the mouth in
contact with the tentacles.
• In other species, the body surface are used
as the major organ of food collection. The
body surface area is increased by lateral
compression and is major areas are coated
with a sticky mucus and colloblast cells.
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26. Means of Food Digestion and
Waste Elimination
• Ctenophores have 4 digestive canals which
lead from the roof of the stomach to the
animal’s aboral surface. 2 of these digestive
canal terminate as blind sacs, while the other
2 canals open wide outside.Undigested
wastes are discharged through anal pores .
Cnidarians, on the other hand, has but one
opening which serves as both mouth and
anus.
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27. Nature of Sexuality
• Ctenophores are hermaphrodites; that
is, a single individual has both male and
female gonads. In contrast, Cnidarians
are gonochoristic, with one sex per
individual.
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28. • A few species reproduce asexually through
fragmentation and the subsequent
development of missing body parts by each
fragment.
• Gonads are located on the walls of some or
all of the gastrovascular canals, so that
gametes are liberated into the digestive tract
and are discharged through the mouth.
• Eggs are fertilized externally.
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30. • Ctenophore cleavage is highly determinate;
cell fates are fixed at the first cell division.
Cell fates of Cnidarian embryos become fixed
later in development.
• Gastrulation,or the formation of distinct inner
and outer germs, are achieve by ctenophores
either by epiboly or by invagination.
Cnidarians gastrulate either through the
process of delamination or by ingression
• Ctenophore embryos develop directly into a
cydippid, while Cnidarians develop into a
ciliated planula larvae
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31. Definition of Terms
• Epiboly : A process in which a sheet of
micromeres spreads over what were the
adjacent macromeres
• Invagination :Process by which groups of
cells push into the blastocoelic space. This
may also be exhibited by some Cnidarians
• Delamination :The cells of the blastula divide
with the cleavage plane approximately
parallel to the surface of the embryo. Thus,
the cells divide into the blastocoel, forming an
inner and outer cell layer, between which the
mesoglea is later secreted
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32. • Ingression :Certain cells become detached
from their neighbors and simply move into the
blastocoel, creating a second layer of cells.
• Cydippid :A miniature ctenophore which is
approximately spherical in shape; is endowed
with 8 comb rows, a fully formed apical sense
organ, and a pharynx; and usually bears a
pair of branched tentacles. It may closely
resemble an adult, though in other modern
species, the cydippid undergoes
metamorphosis before attaining its adult form
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34. Class Tentaculata
A. Order Cydippida
• Tentaculate species closely resemble the
cydippid larvae except that the functional
gonads are present.
• Food is capture through long retractable
tentacles and their side branches.
35. B. Lobata
• Body is compressed laterally, only 4 comb
rows are fully developed, and the tentacles
are generally much reduced in length.
• Large oral lobes, covered with mucus and
colloblasts, constitute the primary food
collection surface.
• The muscular cavity of the 2 oral lobes aids
locomotion in some species. 2 pairs of
ciliated, paddle- or tentacle-like
structure,auricles, assist in prey capture
36. C. Cestida
• The body is so compressed laterally that it
forms a long ribbon, with the mouth and
apical sense organ on opposite sides of its
midpoint.
• Cestids swim through a combination of ctene
activity and sinuous, muscular movements of
the body; only 4 of the comb rows are well
developed in adults.
• Prey are captured by the numerous short
tentacles extending along the extensive oral
edge of the ctenophore.
37. D. Platyctenida
• The oral and aboral surfaces have moved
towards each other, so the body forms a
flattened plate.
• The bottom of the plate is formed largely by a
pharynx, which is extensively and
permanently everted.
• Some species simply float in the water while
others creep slowly over solid substrates
through pharyngeal cilia and muscular
contractions or by muscular flapping of the
lateral lobes of the body..
• The only non-planktatonic ctenophores.
• Has 2 long tentacles.
38. Class Nuda
Beroida
• Has no tentacles and oral lobes.
• Has 8 well developed comb rows.
• Captures and engulfs prey, including other
ctenophores, through muscular lips
surrounding the mouth. The mouth can be
widened to accommodate prey substantially
larger than the predator.
• Thousands of 9 + 2 axonemes enclosed by a
single membrane, Macrocilia, are located just
inside the mouth. These Macrocilia are used
as teeth to chop large prey into bite-size
pieces.
