Chapter 7 - Cnidarians Animals with stinging tentacles, including: jellyfish, corals, sea anemones, and hydra
Cnidarians Cnidarians are soft-bodied animals. Have stinging tentacles arranged in circles around their mouth. May live as single individuals (like anemones) or in colonies (like coral). Have radial symmetry Many cnidarians have a life cycle that includes two stages: 1. Polyp- a sessile flower-like stage. 2. Medusa- a mobile bellshaped stage.
Cnidarian Anatomy Two layers of cells. A saclike digestive tract with one opening (where food enters AND waste exits!) Tentacles which are long flexible appendages arranged in a ring around a central mouth. No brain, but they can respond to stimulus.
Nematocysts Stinging Cells Almost all cnidarians capture their food using stinging cells called nematocysts, which are on their tentacles Each nematocyst is a poison-filled sac containing a coiled spring-loaded dart When another animal touches a nematocyst, it fires, paralyzing its prey
Cnidarian Anatomy Cnidarians do not have a circulatory system, excretory system, nervous system or brain They have a simple nervous system, which is concentrated around the mouth. They have eyespots, which can tell light from dark.
Cnidarian Reproduction Most cnidarians can reproduce sexually and asexually. Asexually- by budding (new organism and detaches from the parent) Sexually- by broadcast spawning (sending sperm out into the water)
Phylum Cnidaria Includes 4 groups: jellyfish (1), sea anemones (2), coral (3) and hydra (4). 3 classes: 1. Scyphozoa 2. Anthozoa 3. Hydrozoa
Cnidarians Jellyfish
The Jellyfish Member of the class Scyphozoa. Umbrella-shaped structure called the medusa, with tentacles hanging down from it. Epidermis: outer layer Mesoglea: jelly-like mass separating the membranes. Gastrodermis: stomach skin.
Jellyfish Movement Jellyfish are considered part of the plankton population; however, they can move. Their muscles can contract the medusa, causing them to pulsate through the water.
Respiration in Jellyfish The membranes of jellyfish are thin: oxygen diffuses directly from water into the animal s cells.
How jellyfish obtain food Cnidoblasts: stinging cells in tentacles. These cells can paralyze a fish with a coiled thread with a barb at the end called a nematocyst. A paralyzed fish can be taken into the jellyfish by its contracting tentacles.
How jellyfish obtain food Jellyfish can also catch food using the medusa. The medusa can be coated in a sticky mucus that traps plankton. Ciliated cells move the plankton to the mouth of the jellyfish.
Jellyfish Reproduction Adult jellyfish release eggs and sperm into water (sexual reproduction). Fertilization = planula larva Polyp grows on a rock or other surface (sessile stage). Polyps clone themselves (asexual reproduction). Ephyra are formed. Adult medusa develops (mobile stage).
Comb Jellyfish Phylum: Ctenophora They have 8 rows of long cilia. They have tentacles for movement/catching food. Bioluminescent.
Cnidarians Anemones
Sea Anemones Member of the class Anthozoa. Anemones have stinging tentacles and a nerve net. Radial symmetry They live attached to a substrate with a muscular foot (sessile).
Sea Anemones: Feeding Very similar to jellyfish. They use stinging tentacles to obtain food. Food is brought to the mouth and digested in the digestive sac by enzymes.
Sea Anemones: Feeding http://www.montereybayaquarium.org/videos/video.as px?enc=0zz+8rd1fkzfmg4uwjabnq==
Sea Anemones: Symbiosis Shrimp and clownfish live among the tentacles: they have a specialized skin coating that protects them from stings. clown fish gain protection from anemone. clown fish protect the anemone s tentacles from being bitten off by other fish.
Life cycle of anemones Anemones do NOT have a medusa stage like the jellyfish. Polyp stage only (SESSILE). They can reproduce asexually by splitting in half. Pieces of a polyps base can break off to make a new organism. They can reproduce sexually by broadcast spawning (releasing sperm into water) fertilized eggs will settle and develop into polyps. http://www.youtube.com/watch?v=vrq7leveddq
Cnidarians The Corals
The Corals Member of the class Anthozoa. Polyp stage only. Coral consists of a small polyp that rests within an expanding bed of limestone. Grow in the tropics. Coral are also the home to symbiotic algae called zooxanthellae.
Symbiosis: Zooxanthellae! Symbiotic zooxanthellae - a photosynthetic algae that gives the corals sugars and oxygen.
How does coral grow? Reefs are a massive limestone structure made of calcium carbonate. To build this structure corals need a source of calcium and carbon. Polyp cells absorb the calcium from sea water. Zooxanthellae take up CO 2 from coral respiration.
Coral Colonies Coral polyps live in large groups and are attached to one another by a thin membrane. Membranes connect the coral digestive systems so that there is sharing of food between polyps.
TED Talk Lesson Conserving our spectacular, vulnerable coral reefs - Joshua Drew Go to this link: http://ed.ted.com/on/rhi5crc4
Cnidarians Hydroids
Hydroids In the class Hydrozoa. Colonial animals: made up of individual polyps that function together. Two types of polyps: 1. Feeding polyps (have nematocysts) 2. Reproductive polyps (have a brief medusa phase)
Portuguese man of war: This organism is classified with hydrozoans and not jellyfish because it is a colony made up of different types of polyps. Like the rest of the cnidarians it has many nematocysts on its tentacles.
Physalia Different types of polyps A gas filled bag keeps the colony afloat one polyp type. Colony of stinging tentacles another type of polyp. Some polyps serve a reproductive function.
Hydroid Reproduction Dominant phase is a polyp. They can reproduce sexually with a brief medusa (free swimming sexual phase). Can also reproduce asexually through budding. http://www.youtube.com/watch?v=wfbhwq95duc