1. Phylum Cnidaria
A highly diverse assemblage that includes jellyfish, sea anemonies, corals and hydras.

2. Characteristics of Cnidaria
Diplobastic Metazoa (Ectoderm and Endoderm).
Radialy Symmetrical.
Specialized Cells Cnidocytes for Feeding.
Two Body Types.
1) Polyp: Benthic.
2) Medusa: Pelagic.

3. CNIDARIA: HYDROZOA HYDRA SP. BUDDING FROM NEBRASKA LINCOLN: POLYP FORM

4. HYDRA SP. TOP VIEW

5. UPSIDEDOWN JELLYFISH: MEDUSA FORM
Cassiopea frondosa

6. Tissue Layers Diploblastic = 2 germ layers mesoglea
endoderm  gastrodermis
ectoderm  epidermis
mesoglea
gelatinous matrix between the 2 layers
gastrovascular
cavity
epidermis
mesoglea
gastrodermis

7. General Body Plan sac-like body (only 1 opening)
Food and waste go in/out the same opening
 no anus!
water within GVC acts as a hydrostatic skeleton
oral surface
mouth
gastrodermis
Gastrovascular
cavity
mesoglea
epidermis
aboral surface

8. General Life Cycle

9. HYDRA SP. FEEDING A B C D

10. Nematocysts specialized stinging organelles
found within cnidocytes (cells)
cnidocytes are located in epidermis
A cnidocyte with a nematocyst within it

11. Nematocysts nematocysts are like “mini-harpoons”
cnidocil senses movement & acts like a “trigger”
can inject poison, coil around prey, or be adhesive
functions:
- prey capture; defense
nematocyst
cnidocil
cnidocyte
Undischarged
Discharged

12. Nematocyst Types

13. HYDRA SP. UNDISCHARGED STENOTELE NEMATOCYSTS

14. HYDRA SP. UNDISCHARGED AND DISCHARGED STENOTELE NEMATOCYSTS

15. HYDRA SP. UNDISCHARGED STENOTELE AND ATRICHOUS ISORHIZA NEMATOCYSTS

16. HYDRA SP. DISCHARGED STENOTELE AND ATRICHOUS ISORHIZA NEMATOCYSTS

17. Nematocyst Discharge

18. Biology Feeding Digestion Gas exchange & Excretion
nematocysts within cnidocytes
tentacles
Digestion
extracellular (in GVC)
intracellular (by gastrodermal cells)
incomplete system (no anus)
Gas exchange & Excretion
these systems are absent

19. Structure Nervous System Skeletal System nerve net
(no central nervous system= no brain)
sense organs
statocysts (equilibrium organs)
ocelli (photosensitive organs)
Skeletal System
Mesoglea; water in GVC acts as a hydrostatic skeleton, and some external skeletal system.

20. Reproduction
Reproduction
Asexual
budding
longitudinal fission

21. Reproduction Reproduction Sexual usually dioecious
(separate sexes e.g. humans)
monoecious
(both male + female gonads in 1 individual)
results in Planula larva

22. Phylum Cnidaria Class Hydrozoa: Freshwater and marine.
Class Scyphozoa: Jellyfish, all marine.
Class Anthozoa: Corals and Anemones, all marine.
Class Cubozoa: Box jellyfish and Sea Wasps, all marine.

23. Class Hydrozoa
medusa & polyp body forms
Fire coral
Millepora

24. Class Hydrozoa medusa & polyp body forms (medusa with velum)
most are colonial
 colonies are formed of individual zooids
a single zooid

25. Class Hydrozoa many of these colonies show polymorphism
 this is where there are several different types of polyps/zooid and each type is specialized for a different function
e.g. gastrozooids = feeding polyps
e.g. dactylzooids = defense polyps
 all the zooids within a colony are genetically identical
 these different zooids work together in the colony

26. Class Hydrozoa - a sessile colony showing polymorphism gonozooid
                                       
entire
colony
gastrozooid

27. Class Hydrozoa
- a Portuguese Man-o-war (Physalia) is a floating hydrozoan colony showing polymorphism
Float
entire
colony
gastrozooid
dactylzooid

28. Portuguese Man-o-war Victims

29. Fire coral victim!

30. Class Hydrozoa- life cycle
sexual
reproduction
asexual
reproduction

31. Class Hydrozoa No Medusa Stage
Hydra is an example of a solitary, freshwater hydrozoan
sexual
reproduction
No Medusa Stage
asexual
reproduction
gonads
bud

32. Class Hydrozoa Hydra is an example of a solitary, freshwater hydrozoan
bud
asexual
reproduction

33. Great Plains Hydrozoans

34. Chlorohydra viridissima: The Green Hydra The green color arises from Chlorella-like unicellular algae each occupying a vacuole in the endodermal cells.

35. Hydra vulgaris The common Hydra

38. Craspedacusta sowerbii
Velum

40. Lives predominantly as a polyp in small lakes, ponds, and old water filled quarries the medusa stage occurs during July-October.

41. Three ways of asexual reproduction
#1) Polyp budding.
#2) Non ciliated planulalike buds may be produced.

42. Three ways of asexual reproduction
#3) Production of medusa buds.

43. Sexual Reproduction
Asexual Reproduction

44. Polypodium hydriforme The most bizarre of the freshwater cnidarians and one of the most unusual species of ALL Cnidarians!!

45. Polypodium spends almost all of its pre-adult life as a parasite of Acipenseriform fishes.

46. LIFE CYCLE