1. Today’s Objectives: 3.4 Describe characteristics of this phylum
Identify life functions of cnidarians
Classify and give examples of phylum Cnidaria

2. Animals with stinging cells
Phylum Cnidaria
Animals with stinging cells

3. Characteristics of Cnidarians
Radial or biradial symmetry
Tissue-level organization
Mesoglea between epidermis and gastrodermis
Gastrovascular cavity
Nerve net
Cnidocytes – used for defense or feeding

4. Life Functions of Cnidarians
Reproduction/life cycle
Can be monoecious or dioecious
Alternate generations between medusa and polyp form
Feeding
Use cnidocytes to stun or kill prey
Can contract tentacles to bring to mouth
Digestion occurs in gastrovascular cavity

5. Life Functions of Cnidarians
Support & locomotion
Hydrostatic skeleton
Some classes have longitudinal muscles for movement
Medusa move by contracting bell or jet propulsion
Some polyps can walk on tentacles, contract, inchworm or glide on pedal disks

6. Reproduction in Cnidarians
Most are dioecious
Polyp can develop through budding or from a free-swimming planula larva
Medusa almost always formed by budding from a polyp body wall

7. Classification of Phylum Cnidaria
Class Hydrozoa
Class Scyphozoa
Class Cubozoa
Class Anthozoa

8. Class Hydrozoa Mostly marine
This is the only class with freshwater members!
Alternate generations
Mostly colonial polyps
Only have cnidocytes in epidermis
Sperm & egg are released outside body
No amoeboid cells in mesoglea

9. Obelia Gastrozooid – feeding polyp formed from planula larvae
Grows through budding into more gastrozooids
Gonozooid – reproductive polyp that forms medusa by budding
Medusae then reproduce sexually

10. Gastrozooid
Gonozooid

11. Gonionemus Medusa predominant - Dioecious
Has a velum (not found in other classes) which creates jet propulsion
Mouth at end of a manubrium
Nerve ring in addition to nerve net that coordinates swimming movements
Statocyst sensory structure that responds to gravity

14. Hydra Freshwater Polyp only, no medusa
Testes form sperm through meiosis
Ovaries form one egg each
Young “buds” from parent until ready to survive on its own, then it drops off

15. Types of Locomotion in Hydra

16. Physalia Portuguese man-of-war Colonial siphonophore
Does not swim, float moved by water and wind
Long dactylozooids (tentacles) contain cnidocytes and kill prey.

17. Class Scyphozoa “True Jellyfish” – polyp form reduced or absent
All marine
No velum
Mesoglea contain amoeboid cells
Cnidocytes in gastrodermis and epidermis
Gametes form in gastrodermis

18. Stinging nettle, Mastigias

19. Aurelia Extensively branched canal system
Gastrodermal cells have cilia to circulate food
Feeds on plankton
Rhopalium – chemosensors
Statocyst – gravity sensors
Lappets – touch receptors
Ocelli – photoreceptors
Planula develop into a scyphistoma polyp

20. Aurelia

21. Life Cycle of Aurelia

22. Class Cubozoa Medusa is cuboidal Tentacles hang from corners
Polyps reduced or absent
Ex. Sea wasp
Class Cubozoa
Venom from one individual can kill 60 adults.
Takes 30 seconds to 4 minutes to kill.

23. Class Anthozoa No medusae, polyp only Mouth has a pharynx
Gastrovascular cavity is divided into sections
Mesoglea contains amoeboid cells
Sexual and asexual reproduction

24. Body structure of Anthozoans
Pedal disk
Oral disk
Siphonoglyph – moves water into gastrovascular cavity to maintain hydrostatic pressure.
Acontia – prevents live prey from damaging gastrovascular cavity.

25. Sea Anemones

26. Corals