Millar Harley Zoology INVERTEBRATES Phylum Cnidaria.pdf

1. INVERTEBRATES (Zool-02506)
3(2-1)
Presented by: Nabeel Tahir
M.Phil. Zoology
Class: ADP 5 Semester
Lecture: 5-6

2. Phylum Cnidaria

3. Who are the Cnidarians?
Hydra
Corals
Sea Anemones
Jellyfish

4. Phylum Cnidaria Characteristics
• Radial Symmetry (or biradial symmetry)
• Diploblastic tissue-level organization
• Gel-like mesoglea between epidermal and gastrodermal
tissue layers
• Gastrovascular Cavity
• Nerve net for a nervous system
• Have cnidocytes – specialized cells used in defense and
feeding

5. Radial Symmetry

6. The Body Wall
• Diploblastic Tissue Level:
• Ectoderm – becomes the epidermis, outer layer of body
wall.
• Endoderm – becomes gastrodermis, inner layer of body
wall.
• Epidermis and Gastrodermis can become many other cell
types.
• Mesoglea – is a jellylike layer between epidermis and
gastrodermis; cells in the mesoglea are from epidermis or
gastrodermis; not triploblastic.

8. Nematocysts
• Cnidocytes – specialized cells of cnidarians that produce
and contain stinging nematocysts; unique to Cnidarians.
• Cnida (ae) – a fluid-filled capsule encasing a coiled hollow
tube; used for attachment, defense, and feeding.
• Some cnidae produce mucus to entrap prey or anchor
the animal
• Nematocyst – a type of barbed cnida that penetrates
prey; often delivers toxins.

9. Nematocyst Discharge
• Nematocyst develops in a capsule in the cnidocyte.
• Operculum (lid): the capsule is capped at its outer margin.
• Cnidocil: Trigger the nematocyst discharge.
• When the cnidocil is stimulated, a rapid (osmotic) influx of water causes
the nematocyst to evert, first near its base, and then progressively along
the tube from base to tip.
• The tube revolves at enormous speeds as the nematocyst is discharged.
• In nematocysts armed with barbs, the advancing tip of the tube is aided in
its penetration of the prey as barbs spring forward from the interior of the
tube and then flick backward along the outside of the tube.

10. Nemotocysts
Discharged
Nemotocyst
Firing Nemotocyst
Nematocyst

11. Alternation of Generations
Most Cnidarians have 2 Body Forms in Life Histories:
1. Polyp – the sessile (attached) state in the
life cycle; cylindrical body and a mouth
surrounded by tentacles; mouth upwards;
usually asexual.
2. Medusa – the free-swimming stage in the
life cycle; shaped like inverted bowl; mouth
usually points downward with tentacles
dangling at margin; usually is dioecious
(either male or female) and produces
gametes.; sexual.

12. Alternation of Generations
• Polyp Form –
attached to substrate
at the aboral end with
mouth facing upward.
•Medusa Form – free
swimming with mouth
usually facing
downward surrounded
by feeding tentacles.

13. Generalized Cnidarian Life Cycle

14. Sexual Reproduction
• Dioecious – either male or female; not
hermaphrodite.
• Sperm or egg released into GVC or released into
water for external fertilization.
• Embryo develops into planula – ciliated, free-
swimming larva.
• Planula attaches to substrate, becomes polyp.

15. Asexual Reproduction
• Polyps may form
from budding from
other polyps.
• Some use fission.
Fission in Sea Anemones

16. Classification of Phylum Cnidarea

17. Class Hydrozoa
• Small, common, marine and freshwater.
• Characteristics:
1. Nematocysts only in epidermis
2. Gametes are epidermal – released into water and not GVC.
3. Incomplete digestive tract with unbranched gut.
4. Mesoglea – is acellular; mostly thin, gel-like.
5. Polyp is dominant body from.
• Most have colonial polyps that are specialized for
feeding, budding, defense.
• Ex. Hydra, Obelia, Gonionemus, Physalia physalis
(Portugese man-of-war)

18. Hydrozoan Life Cycle

19. Hydra
• Freshwater hydrozoan that
lacks a medusa stage.
• Asexually reproduces by
budding from the side of
polyp. Sexual reproduction
occurs in polyp stage.

20. Physalia physalis ,
Portuguese man
of war
(a Hydrozoan),
NOT a true
jellyfish

21. Class Scyphozoa
• All marine, mostly harmless, true jellyfish
• Characteristics:
1. Dominant stage is medusa form.
2. Mesoglea is thicker with some amoeboid cells.
3. Incomplete digestive tract with four branches.
4. Cnidocytes in gastrodermis and epidermis.
5. Gametes are gastrodermal in origin.
• Ex. Aurelia, Mastigias (Stinging nettle)

22. Class Scyphozoa
• Range in size from smaller than a
coin to more than a meter across
with tentacles more than 3 m long
• Most are large planktonic organisms
that swim but also drift with the
current
• Weak swimmers, move by
contracting their rounded body, or
bell
• Feed on almost anything they catch
• Dangerous species – helmet shaped
bells, with long tentacles and fleshy
lobes from oral surface.

23. Scyphozoan Life Cycle

24. Ecological Role of Scyphozoans
• Efficient predators of plankton, crustraceans, fish, etc.
• Prey for leatherback turtle and several species of large
fish—predators move seasonally with jellies.
• Plastic bags, balloons, and small trash often are
mistaken by turtles as jellies and can harm them by
obstructing their digestive tracts.

25. True Jellyfish

26. Cyanea capillata – 7 ft. bell, 120 ft tentacles;
one of the largest

27. Class Staurozoa
• All marine.
• Formerly classified into an order (Stauromedusae) within the class Scyphozoa.
• Lack a medusa stage.
• Resemblance of the oral end of the polyp to a medusa.
• The body form is in the shape of a goblet..
• Nonciliated, crawling planula larva, with very limited dispersal ability.
• 100 described species of staurozoans.
• Found in higher latitudes of the Atlantic Ocean and the northwestern Pacific coast
of North America.
• Others have been found in Antarctic waters, and two species have been
described from abyssal depths in the Pacific Ocean.

29. Class Cubozoa
• Formerly classified as an
order in the Scyphozoa
• Medusa is cuboidal,
tentacles hang from each
corner.
• Polyps are very small
• Active swimmers and
feeders in warm tropical
waters.
• Ex. Sea wasp, box jellies.
Irukandji or Carukia barnesi

30. Class Cubozoa: Box Jellyfish
Irukandji or Carukia barnesi
Chironex fleckeri

31. Portuguese Man o’ War vs. Box Jelly fish

32. Class Anthozoa
• All marine, colonial (corals) or solitary (sea anemones)
• Characteristics –
1. Lack a medusa stage.
2. Cnidocytes have no cnidocils (triggers).
3. Mouth leads to a pharynx and then to the GVC.
4. GVC is divided by mesentaries that bear cnidocytes and
gonads.
5. Mesoglea have amoeboid cells
• Ex. Corals and sea anemones

33. Sea Anemones
• Mostly solitary and
colorful
• Sessile – attach to
surfaces with a pedal
disk; may burrow or
glide on disk. If
threatened, may force
water out GVC and fold
over for protection.

34. Sea Anemones
• Have a hydrostatic skeleton
in GVC and mesentary
compartments.
• Muscle fibers are
gastrodermal.
• May crawl on sides or
thrash about, when
threatened.
• Feed on invertebrates and
fish.

35. Anemone Reproduction
• Asexual (fragmentation or fission) and sexual reproduction – monoecious or
dioecious.
• If monoecious, male gametes mature earlier than female gametes to avoid
self-fertilization – protandry.
• Gametes mature along mesentaries and fertilization is either external or
within the GVC.

36. Rosy Sea Anemone

37. The Other Anthozoan - Corals
• Stony corals form reefs
• Epithelial cells secrete calcium carbonate exoskeleton around base
and sides of column.
• When threatened, polyps retract into exoskeleton.
• Reproduction similar to anemone, asexual budding produces
colonies.

38. Coral Life Cycle

39. Flower Coral – Coral with Exposed Polyps