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PHYLUM CNIDARIA CNIDARIAN LIFE HISTORY Over 9000 species in Phylum Cnidaria Fossil cnidarians date to 700 mya All cnidarians have specialized cells Cnidocyte Contain a specialized stinging organelle called the Nematocyst Found only in this phylum – nowhere else in the animal kingdom CNIDARIAN LIFE HISTORY Cnidarians are mostly found in shallow, marine environments but a few are freshwater – none are terrestrial CNIDARIAN LIFE HISTORY Involved in symbiotic relationships Algae in reef building coral are critical to reef formation Cnidarian diet is almost exclusively algae Algae also feeds other reef inhabitants CNIDARIAN LIFE HISTORY 4 Classes of Cnidarians Hydrozoa CNIDARIAN LIFE HISTORY 4 Classes of Cnidarians Schypozoa CNIDARIAN LIFE HISTORY 4 Classes of Cnidarians Cubazoa CNIDARIAN LIFE HISTORY 4 Classes of Cnidarians Anthozoa CHARACTERISTICS OF CNIDARIA All are aquatic and most are marine Exhibit radial or bi-radial symmetry Most have tentacles which are extensible projections used for food capture CHARACTERISTICS OF CNIDARIA Internal body cavity is called the gastrovascular cavity CHARACTERISTICS OF CNIDARIA Simplest animals with nerve cells No nervous system Have a diffuse nerve net Covers the epidermis CHARACTERISTICS OF CNIDARIA Simplest animals with sense organs the statocyst,which sense gravity and the ocelli, which sense light intensity CHARACTERISTICS OF CNIDARIA Locomotion is by muscle contractions with an outer layer of longitudinal fibers and an inner layer of circular fibers Body support is a hydrostatic skeleton Means it depends on water pressure CHARACTERISTICS OF CNIDARIA Incomplete digestive system with a single opening serving as both anus and mouth No excretory or respiratory system Reproduction may be both sexual and asexual Bud CNIDARIAN FORM & FUNCTION 2 Basic Body Plans Polyp is a hydroid form This is an adaptation to sedentary life Tubular body with a mouth at the oral end surrounded by tentacles and a pedal disc for attachment to a substrate at the aboral end CNIDARIAN FORM & FUNCTION 2 Basic Body Plans Medusa is a bell or umbrella shaped free swimming form CNIDARIAN FORM & FUNCTION 2 Basic Body Plans Medusa is a bell or umbrella shaped free swimming form The mouth is directed downward and may be surrounded by tentacles Found in true jellyfish, class Schypozoa, medusa dominate the lifecycle In class Hydrozoa both life stages are present and alternating CNIDARIAN LIFE CYCLES Medusa and Polyp play different roles in cnidarian life cycles and the life cycles differ in the four classes. The zygote develops into a motile planula larvae which settles and develops into a polyp which may produce other polyps asexually by budding CNIDARIAN LIFE CYCLES The polyp produces medusa by strobilation Medusas are dioecious and reproduce sexually True jellyfish in class Schypozoa have a prominent medusa stage and very small polyps CNIDARIAN LIFE CYCLES Most Hydrozoans have both a polyp and a medusa stage except for the freshwater genus Hydra which has only a polyp stage Class Anthozoa has only a polyp stage CNIDARIAN CNIDOCYTES Most Cnidarians are very effective predators and this is possible because of the cnidocyte. The Cnidocyte holds an organelle that is discharged and contains either toxins or paralyzing agents to render prey helpless These organelles are called cnidae and there are over 20 different kinds of them The most common is called a Nematocyst CNIDARIAN CNIDOCYTES The cnidocyte contains the nematocyst, a trigger hair called the cnidocil a lid called the operculum Both organic molecules and vibrations will trigger nematocyst discharge After a cnidae has discharged, its cnidocyte is absorbed and a new one develops CNIDARIAN CNIDOCYTES Mechanisms of nematocyst discharge “stinging cells” Nematocysts are made of chitin and contain a coiled filament armed with barbs that may contain poisons The cnidocyte cell generates a high osmotic pressure within the capsule which can reach 140 atmospheres of hydrostatic pressure CNIDARIAN CNIDOCYTES When stimulated with vibrations or prey movement, the operculum opens and rapidly releases the coiled barbed threads, this traps the prey and injects the toxin This is the fastest reaction time in the animal kingodm @ 40,000 times the acceleration due to gravity There are only a few jellyfish that are harmful to humans: Sea Wasps or the Portuguese Man of War CLASSES OF CNIDARIA Class Hydrozoa – (hydra) Most hydrozoans are marine and colonial with both polyp and medusa stages: some freshwater hydra lack a medusa stage Freshwater hydra are found world wide with 16 species in North America. The body design is a small tube with a conical elevation at one end called the hypostome which holds the mouth surrounded by 6 – 8 tentacles CLASSES OF CNIDARIA Class Hydrozoa – (hydra) Feed on a variety of small crustaceans, insects and worms Entangle prey and tentacles move trapped prey to mouth. Inside the gastrovascular cavity, gland cells secrete enzymes to digest prey. CLASSES OF CNIDARIA Class Hydrozoa – (hydra) Most Hydra are Dioecious and reproduce sexually by the shedding of eggs and sperm which are produced by temporary gonads stimulated by lower temperatures or stagnant water Encysted larva survive the winter and young hydras hatch in spring Hydras also reproduce asexually by budding CLASSES OF CNIDARIA Class Hydrozoa – Colonial Hydrazoans Hydroid colonies are truly more representative of Class hydrozoa, genus Obelia is a common example studies in the lab Polyp form is predominate with a base, stalk and several types of zooids (An animal arising from another by budding or division, esp. each of the individuals that make up a colonial organism and typically have different forms and functions) Hydranths or gastrozooids are feeding polyps Reproductive polyps are called Gonozoids which release medusa Hydroid medusae are small with a mouth on the underside of the umbrella bell The bell margin holds statocyst and ocelli CLASSES OF CNIDARIA Class Scyphozoa – true jellyfish Most of the larger jellyfish belong to this class Nearly all are free floating in the open sea Bells vary in shape and size but all are mostly water 95% The margin of the umbrella bell has indentations, each bearing a pair of lappets which hold a club shaped rophalium which holds a statocyst that functions in equilibrium and an ocelli which functions in detecting light intensity. CLASSES OF CNIDARIA Class Scypozoa – true jellyfish The mouth leads to a stomach connected to four gastric pouches lined with gastric filaments covered with nematocysts Sexes are dioecious and fertilization is internal in the gastric pouch of the female CLASSES OF CNIDARIA Class Scyphozoa – true jellyfish A complex system of radial canals branch out from the gastric pouches to connect to a ring canal that circles the edge of the bell margin, this makes up the nervous system CLASSES OF CNIDARIA Class Cubozoa – the square / box jellies Square jellyfish with a dominant medusa form and most species have no polyp form The umbrella is square with tentacles extending from each of the four corners Strong swimmers Feed mostly on fish The most deadly of all the jellyfish are in this class Irukiandji and Sea Wasp Irukandji Sea Wasp Irukandji sting CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Anthozoans lack a medusa body form All anthozoans are polyp & are found in both deep and shallow water & vary in size 3 Subclasses of Anthozoans Zoantharia – “flower animals” Ceriantipatharia – “tube anemones” Alcyonarian – “soft corals” CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Sub-class Zoantharia – “flower animals” they are larger and heavier than hydra polyps They attach to rocks, timber and some burrow in mud A crown of tentacles surround a slit-like mouth CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Sub-class Zoantharia – “flower animals” They have a siphonoglyph which is a ciliated groove that leads food downward into the mouth When in danger, water is forcibly expelled through the mouth and the sea anemone contracts into a smaller size Most sea anemones can glide slowly on their pedal disc, some can swim with limited ability CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Sub-class Zoantharia – “flower animals” Symbiotic relationships include Hermit crabs Algae Clown Fish CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Sub-class Zoantharia – “flower animals” Some are dioecious and some are protandrous / monoecious Asexual reproduction takes the form of pedal lacerations when the sea anemone moves to a new location, a small piece tears off and becomes a new anemone Coral Reefs are miniature sea anemones that secrete CaCO3 cups to live in and then a sheet of living tissue forms over the calcareous cups that connects all the gastrovascular cavities, A coral reef is therefore considered one huge living organism CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Sub-class Ceriantipatharia – “tube anemones” Tube anemones live in soft sediment Thorny & black coral form colonies & attach to rocks Both are rare and have few species ; live in shallow seas CLASSES OF CNIDARIA Class Anthozoa – the “flower animals” Sub-class Alcyonarian – “soft corals” Show great variation Have octomerous tentacles around mouth Include Sea Fans, Sea Pens, Sea Pansies and other soft corals ; come in bright colors and help to create the “submarine gardens” of the coral reefs CORAL REEFS Have great biodensity rivaled only by the rain forests Living coral is limited to the top layer above the CaCO3 deposits Coral reefs are great recyclers of Phosphorus and waste CORAL REEFS In order to precipitate CaCO3 from seawater, coral anemones must use CO2 eliminated from photosynthetic algae, so coral reefs are only found where algae can grow They require warmth, light, and full salinity, and clear water This limits their growth to 30 N and 30 S of the equator o o CORAL REEFS Types of Coral Reefs – Fringing Reefs – near land with no lagoon or a very narrow one CORAL REEFS Types of Coral Reefs – Barrier Reefs – parallel to shore with a wide and deep lagoon Great Barrier Reef CORAL REEFS Types of Coral Reefs – Atoll Reefs – encircles a lagoon with a steep bank on the seaward side CORAL REEFS Types of Coral Reefs – Patch or Bank Reefs – located some distance from the shore