Cnidaria and Ctenophora Chapter 7, Zoology

1. Cnidaria and Ctenophora Chapter 7, Zoology

2. Phylum Cnidaria • Pronounced (ny-dar'e-a). • Name means “like or connected with nettles”. • Approximately 9,000 species. • All aquatic; mostly marine, a few freshwater. • All have radial symmetry. • All have two germ (true tissues) layers (diploblastic); the ectoderm and endoderm. • Polymorphism, two body types; polyp and medusa.

3. Phylum Cnidaria • The name is derived from the many stinging cells that they bear called Cnidocytes. • Cnidocytes usually contain stinging organelles called nematocysts. • The nematocysts function as weapons that deliver powerful toxins to kill, paralyze, or injure their prey and/or their enemies.

4. Cnidocytes and Nematocysts

5. Ecology of Cnidarians • Found mostly in shallow, warm equatorial/tropical marine habitats. • Hydra and Sea Anenomes often live symbiotically on mollusc and crab shells. • Jellyfish (medusa) are mostly found in open ocean (pelagic) zones and open lake (limnetic) zones. • Corals play an important role in the ecology of coral reefs by building reefs and providing a habitat for other marine organisms.

6. Dimorphism (Polymorphism) • Cnidarians exhibit polymorphism, meaning they have two different body types. • The sedentary or sessile type that lives attached to the ground surface are called Polyps. • The mobile type that floats is called a Medusa.

7. Description of Polyp Body Form • Cylindrical or tube-shaped body. • Mouth is surrounded by tentacles. • Mouth leads to the gastrovascular cavity. • The aboral end is attached to the ground. • Sea Anemone in the Polyp Body Form

8. Asexual Reproduction in Polyps • There are three different types of asexual reproduction used by polyps. • Budding – A round ball of tissue forms on the side of the polyp and develops into an adult polyp. • Fission – When an adult polyp splits in half and develops into two identical adult clone polyps. • Pedal Laceration – When a piece of tissue is torn from the base of the polyp and develops into a new polyp.

9. Polyps Budding

10. Budding Colonies • In certain species of cnidarians, if buds stay attached to the polyps, a cnidarian colonymay form. • These budding colonies can share food through a common gastrovascular cavity. • Different polyps in a colony that specialize and perform a variety of specific tasks are called zooids. • Gastrozooidsaid in feeding. • Dactylozooidsaid in defense. • Gonozooidsaid in reproduction.

11. The Portugese Man-of-War Example of colonies of zooids in a common cnidarian

12. Description of Medusa • Medusa are the free-swimming or floating body form of a cnidarian. • Medusa are bell-shaped or umbrella-shaped. • The mouth of the medusa (oral side) faces downward and is surrounded by tentacles. • Both the polyp and medusa have a jelly-like fluid in the center of their bodies called mesoglea. • The mesoglea is much thicker in medusa making them buoyant, giving them the name jellyfishes.

13. Medusa

14. Cnidarian Movement • Colonial polyps are stationary • Solitary polyps can move slowly along the surface of the ground by secreting mucus and sliding along their base. • Medusa can move freely by contracting their body and by excreting water out their mouth.

15. Cnidarian Life Cycles • Life cycles of cnidarians can be complex, but in general life begins in the form of a larva called a planula. • The planulasettles and develops into an adult polyp. • Depending on the type of cnidarian, the polyp can remain a polyp for life (like sea anemones and corals) or the polyp may develop into a medusa (like a jellyfish). • Eventually becoming sexually mature and releasing gametes (sex cells) that will unite to form a zygote. • The developing zygote will form into a planula. • Many cnidarians have both polyps (asexual stage) and medusa (sexual stage) for a part of their life.

16. Typical Cnidarian Life Cycle

17. Typical Cnidarian Life Cycle

18. Cnidarian Digestion • The tentacles draw the prey into the mouth. • Digestion begins in the gastrovascular cavity. • Digestive enzymes are secreted in the gastrovascular cavity and the food is broken down into smaller pieces. • After the food is broken down, nutrients get absorbed by the cells lining the gastrovascular cavity. • Eventually the waste is expelled out the mouth.

19. Cnidarian Tissues • The body of a cnidarian consists of three parts, but these are derived from only two (tissues) germ layers. • The outer epidermis (derived from ectoderm) • The inner gastrodermis (derived from the endoderm) • And the middle mesoglea (not a germ or tissue layer)

20. Cnidarian Cells • Cnidarians posses a variety of cells lining or embedded in the epidermis and gastrodermis. • Nutritive-muscular cells – provide support and structure with a hydrostatic skeleton; additionally they also function as digestive cells (found in the gastrodermis). • Gland cells – secrete digestive enzymes (gastrodermis). • Epitheliomuscular cells – provide a protective covering and muscular movement. Contracts tentacles. (epidermis). • Interstitial cells – stem cells that can develop into a variety of other cells including cnidocytes, sex cells, buds, nerve cells etc. (found in the epidermis).

21. Cnidarian Cells • Cnidocytes are the cells that make up the main defense mechanism for cnidarians. • The cnidocytes contain little spines attached to a coil called nematocysts that function as weapons and can injure or paralyze their prey and/or enemies. • There are three types of nematocysts; Those that penetrate and inject poison (penetrants), those that entangle prey (volvents), and those that secrete an adhesive substance (glutinants)

22. Nematocysts

23. Cnidarian Nervous System • No central nervous system (i.e. brain) in Cnidarians. • All of the sensory and nerve cells are connected via a nerve net which is a complex network of cells that are able to communicate and respond to each other.

24. Cnidarian Senses • Some Cnidarians also have some basic sensory cells that are connected to their nerve net. • Statocysts provide equilibrium and balance. • Ocelli are photosensitive and detect light.

25. Class Hydrazoa (hi-dro-zo'a) • Name means “water serpent animal”. • Most Hydrazoa live in marine environments and most also live in colonies. • Some Hydrazoa are solitary and live in freshwater. • Most commonly polyps reproduce asexually and medusa reproduce sexually • Examples of genera include; Hydra, Obelia, Physalia,

26. Hydra and Obelia • Hydra are freshwater cnidarians that are solitary and exist in the polyp body form • Obelia often live in colonies and exist in both the polyp and medusa body form • Solitary Hydra on left and Obelia colony on the right

27. Physalia (Portugese Man-of-War) • Exist as both medusa and polyp forms. • These Hydrazoans form floating colonies. • The nematocysts secrete a powerful neurotoxin that can inflict painful stings. • This portugese man-of-war is actually a colony of hydrazoans.

28. Class Scyphozoa (si-fo-zo'a) • Name means “cup animal” • Includes most of the large common jellyfish • Solitary animals • Scyphozoans are all marine • Polyp stage is often absent • Scyphozoans have a bell-shaped medusa filled with an enlarged mesoglea and they lack a velum. • The velum is a circular membrane surrounding the cap of a medusa that aids in swimming. • Examples of Scyphozoans genera include; Aurelia, Cyanea, Cassiopeia, and Rhizostoma

29. Aurelia and Cyanea • Aureliaon top “moon jellyfish”. • Feeds on plankton caught in mucus on its umbrella • Cyanea capillataon bottom. Called “Sea blubber” by fishermen. • Aka Giant jellyfish or Lion's mane jellyfish) with a bell diameter of 2 meters and tentacles that can reach 60 - 70 meters long.

30. Class Cubozoa (ku'bo-zo'a) • Name means a “cube-shaped animal”. • All marine • Solitary animals. • Very little is known about the life cycle of cubozoans. • Medusa are the primary body form. • The bell-shaped medusa have a square or cube-shaped cross section. • Examples of cubozoa include; Carybdea, Tripedalia, Chironex, and Chiropsalmus

31. Class Cubozoa • Box Jellyfish (Carybdea marsupialis)

32. The Sea Wasp Box Jellyfish (Chironexfleckeri) • Stings are very painful, dangerous and sometimes fatal. Found in the waters of Australia.

33. Class Anthozoa (an-tho-zo'a) • Name means “flower animal”. • All polyps, no medusa. • All marine, some colonial, some solitary. • Found all over the world, in deep, shallow, tropical and polar seas. Very diverse group of cnidarians. • Three different subclasses. • Zoantharia – Sea anemones and hard corals • Ceriantipatharia – Tube anemones and thorny corals • Octocorallia – Soft and horny corals such. These are Corals with an octomerous arrangement.

34. Class AnthozoaSubclass Zoantharia • Sea Anemones and Hard Corals

35. Class AnthozoaSubclass Ceriantipatharia • Tube Anemones and Thorny Corals

36. Class AnthozoaSubclass Octocorallia • Soft and horny corals • Octocorallians are octomerous meaning they usually have an arrangement of eight tentacles arranged around the mouth.

37. Phylum Ctenophora (te-nof'o-ra) • Name means comb bearing. • Ctenophorans are called “comb jellies”. • All marine, less than 100 species known. • Live mostly in warm, tropical waters. • Eight rows of comblike plates lined with cilia used for locomotion. • Radial symmetry like Cnidarians. • Most Ctenophores do not have nematocysts like Cnidarians. Instead they use sticky glue-like cells called colloblasts to capture prey. • Comb jellies are also bioluminescent.

38. Ctenophora (Comb Jellies)