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-The coral is the external lime skeletal cup that is often part of a colony.
-Will form coral reef
-Corals only have a polyp stage
-Polyps have typical coelenterate tentacles armed with nematocytye.
-Coral Skeleton: the calcium cup secreted by the epidermal cells of the cup-enclosed column of the stony corals
-Polyp can withdraw into the cup for protection and the skeleton projects up into folds in the base of the polyp
-Individuals of the colony can be connected through lateral extensions of the body wall
^Such extensions include the gastrovascular cavity
-Internal lime skeleton that is carried radially and upward
-Coral Atolls: a very low lying island, more or less lo==circular in shape, which encloses a shallow lagoon
-Coral reefs can form from a volcanic island that builds a cone close to the surface. Then reef-building corals attach and build a fringing reef close around the island. The coral can continue to grow upward even if island starts sinking as long as the progression is slow, resulting in a barrier reef.
-Reef front (seaward face) grows outward, must of coral is left behind and dies, leaving an exposed reef crest and an area called a reef flat.

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-Although there is no universal agreement, members of this class (Scyphozoa) are sometimes referred to as the "true jellyfish."
-The medusa stage, which has been emphasized to the near or complete elimination of the polyp stage, has an extremely thick layer of the jelly like MESOGLEA making up the major portion of the body mass.
-The body plan is relatively simple, with a layer of EPIDERMIS on the upper and lower surface of the bell, a layer of GASTRODERMIS lining the gastrovascular cavity, and a mass of MESOGLEA contains a number of scattered amoeboid cells, which are not found in the MESOGLEA of hydrozoans.
-The convex upper surface is called the EXUMBRELLAR SURFACE and the concave lower surface is called the SUBUMBRELLAR SURFACE.
-Around the margin of the umbrella, the SUBUMBRELLAR surface contains a NERVE NET and a CIRCULAR MUSCLE layer responsible for the swimming pulsations of the bell.
-The opening to the GASTROVASCULAR CAVITY is through the centrally located MOUTH.
-The MOUTH is surrounded by the nematocyst-equipped ORAL ARMS, which are a drawn-out manubrium.
-Those ORAL ARMS function in capturing small organisms and transferring them to the MOUTH. The MOUTH opens into the gullet, which leads to the stomach.
-The STOMACH opens into four GASTRIC POUCHES, which open into the many RADIAL CANALS of the umbrella.
-These RADIAL CANALS lead into the RING CANAL.
-Digestion occurs within the STOMACH and CANALS of the gastrovascular cavity.
-These canals assure distribution of nutrients to all parts of the jellyfish.
-The four U-shaped GONADS are located in the floors of the GASTRIC POUCHES .
-Gametes (sperm cells and egg cells) are released into the GASTRIC POUCHES, from which they pass out through the MOUTH.
-Fertilization usually occurs in the folds of the ORAL ARMS, and the fertilized egg breaks free to form a larva with an independent existence.
-The margin of the umbrella is fringed with delicate tentacles.
-This margin is further divided into eight sections by indentations, each of which contains a projection called a RBOPALIUM.
-Each RBOPALIUM contains a set of sensory receptors, including a light sensor, two chemical sensors, and a balance sensor.
-The RBOPALIUM is somewhat protected by a pair of tissue flaps called LAPPETS, which some investigators think may also have a sensory function.

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-Oral Disc: circular area with an oval or slit-shaped mouth surrounded by hollow tentacles
-When a prey animal hits tentacles, it is paralyzed by the nematocysts and drawn into the mouth by the tentacles.
-Column: the bulk of the body below the oral disc
^Contains the digestive and reproductive systems.
^Body wall of the column is lined externally with the epidermis and internally with gastrodermis. The middle mesoglea layer is a true connective tissue with motive cells and collagen fibers.
-The MOUTH, with its ring-like canal (ostium), leads into the PHARYNX, which extends into the GASTROVASCULAR CAVITY.
^The PHARYNX, composed of an outer EPIDERMIS, a middle MESOGLEA, and an inner GASTRODERMIS, is suspended from the ORAL DISC and hangs down into the GASTROVASCULAR CAVITY like a circular curtain. Stabilized by its attachments to the complete SEPTA
^One or both sides of the mouth and pharynx will have a longitudinal groove called the SIPHONOGLYPH, which is lined with cilia that beat downward to create an incoming current of water (can bring oxygen/small particles of food)
^Elsewhere on pharynx, cilia beat upward to remove water from the anemone, carrying with it carbon dioxide and other wastes. Process can be reversed to draw food in.
-Interior of the column is divided into sections by partitions called mesenteries or septa.
^Oral end of cavity are paired complete septa, which extend all the way from outer wall of the column to the pharynx and between them are paired incomplete septa
-Cellular arrangement of the septum: two layers of gastrodermis with an inner layer of mesoglea continuous with the mesoglea of the column and the pharynx.
-Ostia: openings in the septa. Allows water to pass from one compartment to the next
-Gonads are located on the sides of the septa in the gastrovascular cavity
-Septal filaments: the interior, lower free margins of the septa that are modified into cords. Contain numerous digestive glands and nematocysts. (lower ends extend beyond the septa as free filaments called ACONTIA and contain digestive glands and nematocysts)
-The base of the anemone is the PEDAL DISC. Its glands secrete a slimy/sticky mucus that helps stick the anemone to the surface. Muscle arrangement includes circular fibers around mouth to retain prey until its digested, circular fibers around upper margin of the column to close the margin of the withdrawn oral disc when anemone is disturbed, longitudinal fibers in the septa and column wall which can cause animal to shorten, and muscle fibers in pedal disc which create a strong suction allowing the sea anemone to attach to an underlying rock.

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-It is shaped somewhat like a bell, with tentacles attached all around the rim. It swims in a pulsating fashion by contracting the bell forcibly to eject water from the opening.
-The convex exterior portion of the bell is called the EXUMBRELLAR SURFACE. The concave interior surface of the bell is the SUBUMBRELLAR SURFACE.
-Both are covered with EPIDERMIS (a layer of cube-shaped cells). The two layers of EPIDERMIS sandwich between them a thick layer of a viscous, jellylike material called MESOGLEA.
^The MESOGLEA stiffens the bell and provides the elasticity necessary to return the bell to its original shape after each of its swimming pulsations.
-Extending inward from the margin of the bell is the VELUM, a circular shelf of tissue containing contractile cells that aid in swimming by reducing the size of the subumbrellar opening, thereby increasing the velocity of the water jet expelled with each contraction.
-The VELUM has two layers of EPITBELIOMUSCULAR CELLS, whose MUSCLE FIBERS run in a circular direction, and two NERVE RINGS, arranged similarly.
-The nerve fibers send off branches to the MUSCLE FIBERS as well as the sense receptors (not shown), located in and between the TENTACLE BULBS.
-Around the external margin of the bell are found the TENTACLE BULBS, each of which gives rise to a TENTACLE.
^The TENTACLES are armed with batteries of SNIDOCYTES containing nematocysts for paralyzing prey.
-Gonolonemus is unusual in having ADHESIVE PADS on its TENTACLES, which it uses at times to attach itself to seaweeds.
-An intriguing feature of gonionemus and its relatives is the GASTROVASCULAR CAVITY, which combines the functions of digestive system and circulatory system,
-A projection of tissue called the MANUBRIUM is suspended inside the bell, and at its lower end is the MOUTH. Food taken into the MOUTH is passed through the GULLET into the STOMACH, where it is digested into a semiliquid state.
-It is then passed in turn into the four RADIAL CANALS, the CIRCULAR CANAL, and the TENTACULAR CANALS, which extend all the way to the tips of the TENTACLES.
-This entire passage is lined with GASTODERMIS, which secretes digestive enzymes to break down the larger pieces.
-These are then absorbed by the GASTRODERMIS for further intracellular digestion. Nutrients reach the cells and tissues by diffusion.
-The GONADS are located in the subumbrellar cavity, attatched to the RADIAL CANALS.
-Sexes are separate in gonionemus, and the eggs or sperm are simply shed into the subumbrellar cavity and pass into the surrounding sea for fertilization and development into polyps.

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-Obelia is a marine animal where a single colony can have hundreds of individuals which means it needs some support. The base and stem obtain this support by means of a base/stem covering, called the perisarc, which is secreted by its epidermal cells.
^Covering is generally transparent
-A colony is attached to rocks and other objects by a base.
^Base gives off branching stems that have numerous polyps on them.
-Polyps are of two kinds, the feeding polyps, and reproductive polyps
^Feeding polyps are like hydras, complete with tentacles and armed with nematocysts for capturing prey. Protected by its own feeding polyp covering into which it can withdraw if threatened. Its gastrovascular cavity, commencing at the mouth if continuous with the gastrovascular cavities (so food captured by one feeding polyp is widely shared)
^Reproductive polyps are protected by a reproductive polyp covering and have no tentacles for capturing food. Instead, they are specialized for budding off MEDUSAE (the free-swimming sexual forms)
-Medusae: capable of sexual reproduction, produce sperm and eggs which are released into the surrounding water.
^Gametes of the opposite sex make contact and fuse in the process of fertilization to form a ZYGOTE. the zygote divides into two cells, then four, then eight, and so on until a hollow ball of cells called a blastula is formed. The BLASTULA grows into a barrel-shaped, ciliated larva called a PLANULA. The planula attaches itself to a rock or some object and forms a NEW POLYP which then grows a new BASE, STEM, and buds new POLYPS to form a new COLONY

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-Examination of the surface of a tentacle shows it is made up of many epitheliomuscular cells
-Between these cells, there are specialized stinging cells called CNIDOCYTES (can be grouped together into "batteries.")
^Each battery consists of several small CNIDOCYTES with coiled, lasso-type (volvent) NEMATOCYTS and a central, large CNIDOCYTE with a penetrating NEMATOCYST.
-As prey passes close to the TENTACLE, it brushes against the long triggers (cnidocils) of the small NEMATOCYSTS.
This may cause an explosive release of threads that entangle the prey.
^The prey contacts the TRIGGER of the large CNIDOCYTE and is quickly impaled by the penetrating thread.
-At the base of a CNIDOCYTE is its NUCLEUS, which contains the genetic material of the cell.
-At the surface is the trigger, which protrudes into the surrounding water. The bulk of the interior of the cell is taken up with the stinging capsule or NEMATOCYST.
-Trigger must receive some chemical as well as mechanical stimulation from the prey, and there may be some nerve control as well.
-A recently fed hydra will fire few, if any, of its NEMATOCYST even in the midst of suitable PREY.
-The NEMATOCYST consists of a fluid-filled CAPSULE with a lid that opens at the time of firing to permit the coiled STINGING THREAD to be turned inside out by a sudden increase in hydrostatic pressure.
-The STINGING THREAD can extend a considerable distance. The BASE OF THE THREAD is often equipped with barbs to aid in holding the PREY.
-Most of the NEMATOCYSTS have open-ended threads that penetrate the PREY to inject it with a paralyzing toxin.

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-Solitary, cylindrical polyps whose mouths are surrounded by 6-10 tentacles
-The body wall of the hydra is soft and smooth
-Basal disc: provides some attachment to the underlying substrate
-Body wall often projects buds of various lengths-a form of asexual reproduction common in hydras
-Bud: a miniature hydra with developing tentacles.
^As the buds nears the end of its development, tentacles and a mouth appear and the bud pinches off the body wall to become an independent organism
-Gonads: ovaries or testes. Develope on the body wall. Situated deep to the epidermis, sex cells arise from the interstitial cells of that layer.
-Tentacles: hollow extensions of the body that surround the mouth. Employed capture of prey, feeding, and locomotion
-Cnidocytes: stinging capsules
-Body wall and tentacles consist of 2 layers of cells separated by a noncellular "connective tissue" layer called MESOGLEA
-Mesoglea: thing, muscuslike layer containing nerve fibers and connecting the epidermal and gastrodermal cell layers. Does not constitute a true connective tissue.
^Outer layer called the epidermis and consists of at least four cell types. EPITHELIOMUSCULAR CELLS are the principal lining cells (bases are contractile and may be stimulated by the nerves in the mesoglea). Contraction of these cells makes it possible for the hydra to alter its body shape significantly. CNIDOCYTES contain stinging capsules and may be fitted within previous cells like a glove. INTERSTITIAL CELLS are the "mother cells" and sex cells are formed from these. All replacement cells are generated from these. NERVE CELLS of the epidermis have nerve fibers that extend through the mesoglea and connect with epitheliomuscular cells (initiating contraction) as well as sensory nerve cells in the gastrodermis.
-Gland cells (2) secrete enzymes into the gastrovascular cavity and aid the digestive process. Interstitial cells (3) of the gastrodermis are associated with the regeneration of new cells. The nerve cells believed to be largely sensory and are sensitive to the gastrovascular cavity environment.
-Water and water-borne traffic come into the gastrovascular activity and leave via the same orifice (mouth)

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-Unattached, motile stage in cnidarians and is found swimming freely in the water column.
-Swimming is done by muscular contraction of the dome-shaped umbrella, or bell, which forces  water out and propels the medusa in the opposite direction.
-As the umbrella muscles contract the bell, fibers of the protein collagen in the umbrella are compressed
-When muscles relax, the elastic recoil of the compressed collagen fibers causes the bell to expand and refill with water
-POLYORCHIS: a high-domed umbrella that is transparent and clearly reveals the organs within the umbrella space.
^The elongate, mouth-bearing manubrium protrudes through the opening of the umbrella
^Opens to stomach then to radial canals
^Beneath are elongated gonads (reproductive organs)
^Tentacles bear nematocysts that sting and capture zooplankton/other small marine animals
-AURELIA: squat, milky translucent medusa. Jellyfish with no manubrium, relatively short tentacles. and four elongated oral arms that surround the mouth opening
^Does not catch prey with tentacles, instead, it is a suspension feeder. As it sinks, Aurelia catches plankton in the mucus on the inside of the umbrella. the mucus-covered food is then carried to the margin of the umbrella and scraped off by oral arms. Arms have ciliated grooves that carry food to the mouth.
-PELAGIA: purple and translucent gray umbrella.
^Four oral arms are very maneuverable; nematocysts bearing arms entrap and subdue small organisms swimming into them
-HALICLYSTUS: Attaches itself to surf grass unlike most medusae
^Small, stalked attachment disc protrudes from the upturned umbrella. Able to absorb pigment from the plant to which they attach, thus changing the color of their umbrella to match their substratum

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-The polyp is attached by its pedal disc to the substratum, with its mouth and tentacles facing upward
-Body is basically cylindrical in shape
-Oral disc at the top end, and a pedal disc.
-Pedal Disc: anchors the anemone to a solid substratum
-Some attach to solid surface, burrow, or attach themselves to the shells of other animals
-SQUAT ANEMONE: a giant green sea anemone of Pacific coast tidepools. Feeds on nearly any organisms that are washed or swim unaware into its green tentacles
-LONG-COLUMNED, WHITE-PLUMED SEA ANEMONE: numerous fine tentacles can reach into the current to capture small organisms carried by the moving water
-CORAL POLYP: similar to the sea anemone.
^The individual's polyps of a coral colony are connected by a      continuous layer of body tissue.
^Each polyp has a calcium carbonate skeleton into which the entire polyp can contract.
^The cup-shaped skeletons are secreted by the polyps epidermis and are the basic structural units that form tropical reefs
-Polyps of marine hydroids can occur in colonies, forming branched structures that may be attached to various substrata.
^An individual polyp is specialized for feeding or reproduction/
^Obelia are feeding polyps, called gatrozooids, and reproductive polyps are called gonozooids.
^Small medusae are produced asexually on the gonozooids and then swim away