Characteristics and Life Functions of Phylum Cnidaria

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

2. 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 scyphistomapolyp

20. Aurelia

21. Life Cycle of Aurelia

22. Class Cubozoa • Medusa is cuboidal • Tentacles hang from corners • Polyps reduced or absent • Ex. Sea wasp

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