Cnidaria & Ctenophora Characteristics - Include Hydras, jellyfish, sea anemones & corals -Radially symmetrical Two basic forms: Polyp: Cylindrical form which attach bases (Sessile) Hydras, anemones Medusa: Bell-shaped, mouth down version of the polyp. Moves freely Polyp Marine Freshwater Medusa Body Plan • They have tissue layers • Outer layer of cells - the epidermis • Inner gastrodermis, which lines the gut cavity or gastrovascular cavity (gastrodermis secretes digestive juices into the gastrovascular cavity) • In between these tissue layers is a noncellular jelly-like material called mesoglea Movement & Nervous System • The cnidarian body is capable of some kind of coordinated movement • Both the epidermis and the gastrodermis possess nerve cells arranged in a loose network - nerve net (plexus), which innervate primitively developed muscle fibers that extend from the epidermal and gastrodermal cells • Stimulus in one part will spread across the whole body via the network Movement & Nervous System Nutrition • Cnidarians are carnivores • hydras and corals consuming plankton • sea anenomes & jellyies consuming small fish & clams • Use tentacles to capture prey and direct it toward the mouth • Digested in the gastrovascular cavity where gland cells secrete enzyme that digest prey. • The gastrovascular cavity exists as 1 opening for food intake and the elimination of waste. IN one cavity; OUT the same cavity • There is no system of internal transport, gas exchange or excretion; all these processes take place via diffusion Cnidocytes • Prey capture is enhanced by use of specialized stinging cells called cnidocytes located in the outer epidermis. • Each cnidocyte has a modified cilium - cnidocil, and is armed with a stinging structure called a nematocyst. • The undischarged nematocyst is composed of a long coiled thread • When triggered to release, either by touch or chemosensation, the nematocyst is released from the cnidocyte and the coiled thread is inverted • Some nematocysts function to entangle the prey; others harpoon prey and inject a paralyzing toxin Cnidocytes • Nematocyst Animation: Feeding Tentacles – http://vimeo.com/37431528 • Nematocyst Animation: Fighting Tentacles – http://vimeo.com/37432287 Portuguese Man O' War Box Jellyfish Reproduction • One of the most amazing adaptations is the ability of some cnidarians to regenerate lost parts or even a complete body • Asexual reproduction is common with new individuals being produced by budding • Sea anenomes engage in a form of asexual reproduction called pedal laceration (pieces break off and regenerate new clones) • Fertilization is external, with the zygote becoming a elongated, ciliated, radially symmetrical larva - planula larva Life Cycle Cnidarian Taxonomy Class Hydrozoa: The Hydras • Can be found in freshwater; most are marine • Live solitary or colonial lives • Life cycle includes both asexual polyps and sexual medusa stages; or neither or both. • Freshwater hydras are found in ponds and streams • Mouth opens to the gastrovascular cavity • The life cycle is simple: eggs and sperm are shed into the water and form fertilized eggs; planula is by passed with eggs hatching into young hydras • Asexual reproduction via budding Colony – Budding were bud stays attached to main stalk. Adding more and more. Class Hydrozoa: Hydra Colony: Tubularia crocea Class Hydrozoa: Hydra Colony: Tubularia crocea Class Hydrozoa cont. Life Cycle of Obelia • Gonozooids release free swimming medusae • Zygotes become planula larvae, which eventually settle to become polyp colonies • The medusae of hydroids are smaller than those of jellyfishes (C. Scyphozoa) • Also, the margin of the bell projects inward forming a shelf-like velum Class Hydrozoa Cont… Portuguese Man O' War • Actually a floating colony of four different polyps which are connected by tissues. • Body polyp consists of a nitrogen- filled bladder which floats on top of the water. • Reproductive polyp • Feeding polyp • Defense polyp - tentacles that are typically 10 m (30 ft) in length but can be up to 50 m (165 ft), which contain toxic nematocysts. Class Scyphozoa: The Jellies • Typical “Jellyfish” • Umbrella-shaped bell (medusa) and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey. • Contain massive amounts of mesoglea (95-96% water) • Bell – • Manubrium - stalk-like structure hanging down from the centre of the underside, will reach out for prey then grabs it with its mouth • Velum – shelf-like inward fold that increases water jet flow • Statocysts ( gravitational detectors or balance sensory ) • Ocelli – photoreceptor cells • Hydrostatic skeleton – based on water filling up cavaties. • Radial Canal – aid in moving food from stomach • Rhopalia - sensory structors • Gonads - sexual gland • Tentacles – • nematocysts • ~+500 million years, oldest tissued organism. Class Scyphozoa: The Jellies Scyphozoan Life Cycle - Aurelia • Gametes develop in gastrodermis of gastric pouches; eggs and sperm are shed through mouth • Fertilized eggs develop into a planula larva; settles on substrate and develops into a polyp - scyphistoma • Scyphistoma produces a series of polyps by budding - strobila • The polyps undergo differentiation and are released from the strobila as free swimming ephyra • Ephyra matures into an adult jellyfish Class Cubozoa: Box Jellies • Similar in form to scyphozoans • Box-shaped medusa allows it to move more rapidly than other jellyfish. • Four corners of the bell contains a cluster of 15 tentacles up to 3 meters long covered with millions of cnidocytes • Four eye-clusters with twenty-four eyes, complete with retinas, corneas and lenses. • Tests have shown that they have a limited memory, and have a limited ability to learn • Diet that consists of fish, worms, and crustacean arthropods. • Mostly found in the Indo-Pacific, but some species are found many other areas of the world • Chironex fleckeri -One of the most venomous creatures in the world. • Strong toxin, causes immediate, extreme pain • Death can occur 3-20 min after a sting Class Cubozoa: Irukandji jellyfish • Carukia barnesi • Extremely venomous jellyfish that inhabit marine waters of Australia • Bell about 5 mm - 10 mm wide and four long tentacles, which range in length from just a few centimeters up to 1 meter. • Nematocysts are in clumps, appearing as rings of small red dots around the bell and along the tentacles • Venom is very powerful, 100 times as potent as that of a cobra Class Anthozoa: Anemones • Do not have a medusa stage in their development. ONLY Polyp • Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which it grows • They attach to shells, rocks, timber, etc. by pedal discs; some burrow in mud or sand. • Most anemones can glide slowly on pedal discs; some can swim with limited ability. • A crown of tentacles (nematocysts) surrounds the flat oral disc. • A slit-shaped mouth leads into a pharynx. • The siphonoglyph is a ciliated groove that creates the water current into the pharynx. • Currents carry in oxygen and remove wastes, and maintain fluid pressure for a hydrostatic skeleton. • When in danger, water is rapidly expelled through pores as the anemone contracts to a small size. • Most harbor symbiotic algae; some have a mutualistic relationship with clown fish. Class Anthozoa: Anemones Class Anthozoa: Corals Scleractinian Corals •Also known as true or stony corals. •They are miniature sea anemones that live in calcareous cups they have secreted. •A sheet of living tissue forms over the coral surface, connecting all gastrovascular cavities. Coral Reefs •Living plants and animals are limited to the top layer above the calcium carbonate Coral Polyps deposits. •These corals require full salinity of seawater and warmth and light, limiting them to waters between 30 degrees north and south. Fringing Reefs Barrier Reefs Atolls Phylum Ctenophora: Comb Jellies • 8 comb rows • Have colloblasts: sticky ends that are used to capture prey • Catch food with tentacles • Bioluminescent • All marine • Most are pea-size to golf ball-size .