Phylum cnidaria and coelentrates presentation Best of Luck

1. Coelenterates
or
Cnidarians
Lecture 4

2. Phylum Coelenterate
• Coelenterata is scientifically classified from the
Animalia kingdom and Eumetazoa sub-kingdom.
• The term Coelenterata is no longer recognized as
scientifically valid, as the Cnidaria and Ctenophora.
• This phylum includes about 9000 species , which are
mainly marine ; few are fresh water .
• The name of this phylum came from the stinging cells
or cnidoblasts present on the ectoderm of tentacles and
the body of these carnivorous animals.
• This phylum includes aquatic (marine and fresh water),
solitary or colonial forms

3. Characteristics of Phylum Cnidaria
• Radially symmetrical animals
• No anterior or posterior ends.
• Directions are based on the position of the mouth opening
• Mouth containing end is the oral end
• Opposite end is the aboral end.
• Radial symmetry is advantageous for sedentary animals because sensory receptors are evenly
distributed around the body. These organisms can respond to stimuli from all directions.

4. • Gelatinous mesoglea between the epidermal and gastrodermal tissue layers
• Gastrovascular cavity
• Nerve cells organized into a nerve net
• Specialized cells, called cnidocytes, used in defense, feeding, and attachment
• Diploblastic
Characteristics of Phylum Cnidaria

5. The Body Wall and Nematocysts
• The ectoderm gives rise to epidermis, while
endoderm to gastro dermis. Both perform
different functions
• Protection
• Food gathering
• Coordination
• Movement
• Digestion
• Absorption
• Jellylike mesoglea is present.

6. Cnidocytes produce structures called cnidae (fluid-filled, intracellular capsule enclosing a
coiled, hollow tube)
The cnidocyte usually has a modified cilium, called a cnidocil.
30 kinds of cnidea, 6 or more present in one individual
The Body Wall and Nematocysts

7. Alternation of Generations
• Many cnidarians possess two body forms in their life histories
• The polyp is usually asexual and sessile. It attaches to a substrate at the aboral end, and has a
cylindrical body, called the column, and a mouth surrounded by food-gathering tentacles.
• The medusa is dioecious and free swimming. It is shaped like an inverted bowl, and tentacles
dangle from its margins.

8. Generalized Cnidarian Life Cycle

9. Maintenance Functions
• The gastrodermis of all cnidarians lines a blind-ending gastrovascular cavity.
• This cavity functions in digestion, the exchange of respiratory gases and metabolic wastes,
and the discharge of gametes.
• Food, digestive wastes, and reproductive stages enter and leave the gastrovascular cavity
through the mouth.

10. Digestive system
Role of Nematocysts in digestion
• Feed small crustaceans and small fishes, Entangle ad paralyze prey
• Contractile cells in tentacles shorten ad food moves inward
Gastrodermal gland
• Mucus and enzymes (food to soupy broth)
Nutritive muscular cells
 Phagocytize partially digested food into food vacuoles
 Circularly oriented contractile fibers that help move material into and out of
gastrovascular cavity by peristaltic contraction
 Expelling undigested food through mouth

11. Hydrostatic skeleton
• Gastrovascular cavity act as hydrostatic skeleton
• Epithelio-muscular cells are contractile and help in
movement
• By contraction of Epithelio-muscular cells polyp
bends toward that side and mouth is opened, water
escapes and polyp collapses
• If mouth do not open the polyp elongates

12. Locomotion
 Polyp
• Somersaulting
• Inch worm fashion
• Glide ( base attach on substrate and tentacles
move)
 Medusae
• Floating (water currents ad wind for
horizontal movement)
• Swimming (contraction of circular and
radial Epithelio-muscular cells cause
rhythmic pulsation of the bell propelling
medusa through water

13. Nervous System and Sensory Receptors
• Nerve cells under epidermis and near mesoglea interconnect to form two dimensional nerve
net
• Nerve net conducts impulses around the body in response to localized stimulus
• Receptors for perceiving touch and chemicals distributed throughout the body
• Have large surface area to volume ratio
• All cells are at a short distance from body surface
• Oxygen, Carbon dioxide and nitrogenous wastes are exchangd with the environment by
diffusion

14. Class Hydrozoa
• 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
• Hydra is a common freshwater hydrozoan
• Large oceanic hydrozoans belong to the order Siphonophora
• Medusae usually with a velum; many polyps colonial; mostly marine with some freshwater
species.
• Examples: Hydra, Obelia, Gonionemus, Physalia

15. Class Hydrozoa

16. Class Scyphozoa
• Medusa prominent in the life history, Polyp small
• Gametes gastrodermal in origin and released into the gastrovascular cavity
• Cnidocytes present in the gastrodermis as well as epidermis
• Medusa lacks a velum Mesoglea with wandering mesenchyme cells of epidermal origin
• Example: Aurelia
Mastigius spp. Aurelia aurita

17. Structure of a Scyphozoan Medusa

18. Aurelia Life History

19. Class Staurozoa
• Medusae absent
• Develop from benthic planula larvae
• Eight tentacles surrounding the mouth
attachment to substrate by adhesive disk
• Sexual reproduction only
• Marine
• Haliclystis.

20. Class Cubozoa
• Medusa prominent in life history
• Polyp small
• Gametes gastrodermal in origin
• Medusa cuboidal in shape with tentacles
that hang from each corner of the bell
• Marine
• Chironex

21. Class Anthazoa
• Colonial or solitary polyps
• Medusae absent
• Cnidocytes present in the gastrodermis
• Cnidocils absent
• Gametes gastrodermal in origin
• Gastrovascular cavity divided by
mesenteries that bear nematocysts
• Internal biradial or bilateral symmetry
present mesoglea with wandering
mesenchyme cells tentacles solid
• Marine.
• Anemones and corals. Metridium.