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What do these animals have in common? Phylum Cnidaria “the jellies” What is a cnidarian? •invertebrates •more than 9000 species •jellyfishes, corals, sea anemones, and hydras. •worldwide •all but a few are marine • two distinct body forms during their life cycles Medusa Polyp • polyp = sessile form •mouth surrounded by tentacles. - sea anemones, corals, and hydras. • medusa = free-swimming form - jellyfish Body Form The Medusa -an umbrella-shaped, - floating body = a bell, with mouth on underside. Tentacles Body Form mouth The Polyp Attached to substrate, mouth on top surrounded by tentacles Body form One body form may be more often seen than the other. In jellyfishes, the medusa form is usually observed. In hydras, polyp form is most common form of hydras. http://www.microscope-microscope.org/gallery/Mark-Simmons/pages/hydra2.htm Body form Most cnidarians undergo a change in body form during their life cycles. Medusa Polyp At some point, most Cnidarians exist as both a polyp and a medusa. Body structure Mouth Tentacle • radially symmetrical • one body opening • two cell layers How is this similar to sponges? Cavity Inner cell layer Bud Jellylike layer Outer cell layer Disc Body structure • cell layers are organized into tissues with specific functions - true tissues - inner layer mainly assists in digestion -surrounds the GASTROVASCULAR CAVITY Mouth Tentacle Cavity Inner cell layer Bud Jellylike layer Outer cell layer Disc Body structure • two cells layers allows easy diffusion of: - Oxygen - dissolved in water, it can diffuse directly into body cells. - Carbon dioxide /other wastes - moves out of the body cells directly into the surrounding water. Reproduction in cnidarians • sexual and asexual reproduction Sexual reproduction •occurs in only in the Medusa phase if it has both forms in life cycle IF there is NO medusa stage, then the polyp can reproduce sexually. Sexual Reproduction in Cnidarians Both the medusae and Eggs polyps are Fertilization diploid Female Male (2n) Asexual Reproduction animals. Blastula Bud Larva Diploid = 2 full sets of Polyp chromosomes Per body cell Nematocyst before discharge Nematocyst after discharge Digestion in cnidarians • Predators - capture or poison prey using nematocysts - a capsule that contains a coiled, threadlike tube. -tube may be sticky or barbed, and may contain toxins - located in stinging cells that are on tentacles Digestion in cnidarians Once captured by nematocysts, prey is brought to the mouth by contraction of the tentacles. Mouth Polyp Gastrovascular cavity Mouth Medusa • Food enters gastrovascular cavity • digestive cells release enzymes to break down prey •undigested materials are ejected back out through the mouth. Diversity of Cnidarians There are four classes of cnidarians: • Hydrozoa •Anthozoa •Scyphozoa •Cubozoa Class Hydrozoa •2 groups - hydroids (hydra) - siphonophores (Portuguese man-of-war) • marine animals •Most hydrazoans go through both stages • Hydra - polyp stage only •reproduce by budding •found attached to piers, shells, and other surfaces. daphnia Sea monkey development budding #1 Class Hydrozoa The siphonophores - floating colonies -drift about on ocean’s surface. The Portuguese manof-war, Physalia, is an example of a siphonophore hydrozoan colony Different functions for different individuals Class Anthozoa • exhibit only the polyp form. • Corals • Sea anemones • Sea fans Sea apple feeding Corals • live in colonies of polyps in warm ocean waters around the world. • secrete protective, cuplike calcium carbonate shelters around their soft bodies. •Colonies of many coral species build the coral reefs •provide food and shelter for many other marine species. Corals Corals that form reefs are = hard corals. • soft corals= do not build calcium carbonate structures – not reef builders. Corals Living portion of a coral reef is a thin, fragile layer •grows on top of the shelters left behind by previous generations. Often found in •shallow, •nutrient-poor waters, •thrive because of symbiotic relationship with microscopic, photosynthetic protists called zooxanthellae. Bleaching Worldwide •Zooxanthellae •produce oxygen and food that corals use, •Uses carbon dioxide and waste materials produced by the corals •cause bright colors found in coral reefs. •free-swimming, sometimes leave the corals •Caused by warming ocean temperatures and •Increasing acidity due to increased CO2 in atmosphere •Corals die without them = “bleaching” •70% bleached in 20-30 yrs; 35 million acres so far • Coral reefs provide habitat for 25% of marine fish • About 1 billion people rely on fish as their primary food source • Tourism – over a billion dollars is spent every year in the Caribbean, Australia (3.9 billion/year), and the Pacific Islands • 1.2 Billion in Florida each year • Most diverse ecosystem – “Ocean Rainforest” • 4000 species of fish, 800 species of coral • Corals are used for pharmaceuticals • Chemical extracts from corals have helped create drugs to treat AIDS, Cancer, Arthritis, Inflammatory disorders, and pain killers • Beneficial for patients with heart, kidney, and liver transplants. Class Scyphozoa = jellyfish •Fragile •sometimes luminescent bodies • Some are transparent •May be pink, blue, or orange. Medusa form is the dominant stage in this class. Class Scyphozoa • muscle-like cells in outer cell layer can contract • When these cells contract , the bell contracts • propels the animal through the water. Class Cubozoa • Box jellyfish • Originally included in Class Scyphozoa. • Differences: – – – – – Their bells are square-shaped, instead of round They have primitive brians They have eyes They swim, not float They sleep Class Cubozoa • The Irukandji in Australia is one of the most dangerous animals • It is very small, only 2.5 cm from bell to tentacles Giant Jellyfish • Japan has been invaded by Nomura’s jellyfish – the giant jellyfish. Research: • • • • • What are Nomura’s Jellyfish? Where are they found? Just Japan? What causes them to get so big? Are they dangerous? Are they new? Or are they only now getting noticed? Giant Jellyfish • 6.5 ft wide and 450 lbs • More common in China and Korea • Only recently in Japan Giant Jellyfish • Not much is known, Japan studying mating/migration habits • Choking fishing nets • Possible warmer seas (global warming) causes increase in population • http://video.google.com/videoplay?docid=2208948115892996006&q=giant+jellyfish&t otal=103&start=0&num=10&so=0&type=search&plindex=0 Where did they come from? The earliest known cnidarians also date to the Precambrian, about 630 million years ago. The earliest coral species were not reef builders, so reefs cannot be used to date early cnidarians. The larval form of cnidarians resembles protists, and because of this, scientists consider cnidarians to have evolved from protists.
