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 layers (diploblastic); the ectoderm and endoderm. • Polymorphism, two body types; polyp and medusa.

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

4. Cnidocytes and Nematocysts

5. Ecology of Cnidaria • Found mostly in shallow marine habitats and in warm equatorial/tropical waters. • Colonies of Hydra and Solitary Sea Anenomes can be found symbiotically living on mollusc and crab shells. • Floating medusae can be 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 or plans. • The sedentary or sessile type that lives attached to the ground 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. • Anemone in the Polyp Body Form

8. Asexual Reproduction in Polyps • There are three different ways a polyp can reproduce asexually. • Budding – A round ball of tissue forms on the side of the polyp and develops into an adult polyp with a functional mouth and tentacles. • Fission – When an adult polyp splits in half and develops into two identical adult clones. • Pedal Laceration – When tissue is torn from the base of the polyp and develops into a new polyp.

9. Polyps Budding

10. Budding Colonies • If buds stay attached to the polyps, a cnidarian colony can develop. • Budding colonies can share food through a common gastrovascular cavity. • Different polyps in a colony that specialize and perform 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 free-swimming or floating. • Medusa are bell-shaped or umbrella-shaped. • The mouth of the medusa (oral side) faces downward and is surrounded by tentacles around the rim. • Both the polyp and medusa have a jellylike 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 • The life cycles of cnidarians can be complex, but in generallife begins in the form of a larva called a planula. • The planula eventually settles and develops into a 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.

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, it gets absorbed by the cells lining the gastrovascular cavity. • Eventually waste is expelled out the mouth.

19. Cnidarian Cells and Tissues • The body of a cnidarian consists of three parts • The outer epidermis (derived from ectoderm) • The inner gastrodermis (derived from the endoderm) • And the middle mesoglea

20. Cnidarian Cells • Cnidarians posses a variety of cells 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 muscularmovement (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 – These cells are the defense mechanism of the cnidarians. • They contain little spines attached to a coil called nematocysts that can injure or paralyze their prey and enemies. • There are three main types of nematocysts; Those that penetrate and inject poison (penetrants), those that entangle prey (volvents), and those that secrete a sticky adhesive substance (glutinants)

22. Nematocysts

23. Cnidarian Nervous System • No central nervous system 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 live in colonies. • Occasionally Hydrazoa live in freshwater and are solitary. • 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 acting as one unit.

28. Class Scyphozoa (si-fo-zo'a) • Name means “cup animal” • Includes most of the large common jellyfish • Solitary animals • All scyphozoans are marine • Polyp stage is sometimes absent • Bell-shaped medusa filled with an enlarged mesoglea and lacking 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. • Giant jellyfish (also known as lion's mane jellyfish) with a bell diameter of 2 meters and tentacles that can reach up to 60 or 70 meters long.

30. Class Cubozoa (ku'bo-zo'a) • Name means a “cube-shaped animal”. • 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 in deep, shallow, tropical and polar seas. • Three different subclasses. • Zoantharia – Sea anemones and hard corals • Ceriantipatharia – Tube anemones and thorny corals • Octocorallia – Soft and horny corals such as sea pens, sea fans, and sea pansies. 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 “comb jellies”. • All marine, less than 100 species known. • Live mostly in warm tropical waters. • Eight rows of comblike plates 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)