Phylum Cnidaria -

Phylum Cnidaria -

Phylum Cnidaria Hydras, jellyfish, sea anemones, and corals belong to the phylum Cnidaria. these diverse animals are all armed with stinging cells called nematocysts The name Cnidaria comes from the Greek

word "cnidos," which means stinging nettle. Casually touching many cnidarians will make it clear how they got their name when their nematocysts eject barbed threads tipped with poison.

Cnidarians have two basic body forms, and both show radial symmetry. Medusa forms are free-floating, jellylike, and often umbrella-shaped. Polyp forms are tube like and are usually attached to a rock or some other object.

Polymorphic- alternates between polyp and medusa General Characteristics 1. Radial symmetry is primary 2. Gastrovascular cavity for digestion

3. Tentacles - feeding, locomotion, defense Reproduction in polyps is by asexual budding (polyps) or sexual formation of

gametes (medusae, some polyps). Cnidarian individuals may be monoecious or dioecious. The result of sexual reproduction is a planula larva, which is ciliated and freeswimming. Embryo --> planula --> polyp or medusa

Classes Class hydrozoa- hydra, fire coral, Portuguese man-of-war Class scyphozoa- jelly fish Class cubozoa- box jellies Class Anthozoa-anemones, corals

Hydrozoa 2700 species of hydras, colonial hydroids, fire corals

polyp, medusa, polymorphic Hydra

Freshwater Hydrozoa Hydras live in quiet ponds, lakes, and streams. They attach to rocks or water plants by means of a sticky secretion they produce in an area of their body called the basal disk

Marine hydrozoans are typically far more complex than freshwater hydrozoans. Often many individuals live together, forming colonies Most hydrozoans are colonial organisms whose polyps reproduce asexually by

forming small buds on the body wall. Many hydrozoans are also capable of sexual reproduction. During sexual reproduction, the medusas release sperm or eggs into the water. The gametes fuse and produce zygotes that develop into free-swimming, ciliated larvae

called planulae. Feeding Hydra mainly feed on small aquatic invertebrates such as Daphnia and Cyclops (water flea). When feeding, Hydra extend their body to

maximum length and then slowly extend their tentacles. Despite their simple construction, the tentacles of Hydra are extraordinarily extensible and can be four to five times the length of the body

Tissue Differentiation and Body Wall a. Epidermis interstitial cells - capable of forming other tissues nerve cells - sensory and motor

cnidocytes - discharge nematocysts, used once b. Mesoglea jelly-like matrix, mostly acellular, fluid or rigid c. Gastrodermis nutritive-muscle and enzymatic cells

Hydra dance video Hydra eating video Portuguese Man-of-war Despite its outward appearance, the man o'

war is not a jellyfish but a siphonophore, which differs from jellyfish in that it is not actually a single organism, but a colonial organism made up of many minute individuals called zooids. they are attached to one another and physiologically integrated to the extent that

they are incapable of independent survival The Portuguese man o' war lives at the surface of the ocean. The gas-filled bladder,

or pneumatophore, remains at the surface, while the remainder is submerged.Since the man o' war has no means of propulsion, it is moved by a combination of winds, currents, and tides

It is composed of four types of polyp. One of the polyps, a gas-filled bladder called the pneumatophore (commonly known as the sail), enables the organism to float. This sail is bilaterally symmetrical, with the tentacles at one end, and is translucent, tinged blue,

purple, pink, or mauve. It may be 9 to 30 centimetres (3.5 to 12 in) long and may extend as much as 15 centimetres (5.9 in) above the water.

The other three polyp types are known as dactylozooid (defence), gonozooid (reproduction), and gastrozooid (feeding).These polyps are clustered. The dactylzooids make up the tentacles that are typically 10 metres (33 ft) in length but can be up to 50 metres (160 ft

Diet The Portuguese man o' war is a carnivore. Using its venomous tentacles, a man o' war traps and paralyzes its prey. Typically, men

o' war feed upon small aquatic organisms, such as fish and plankton. The predators The loggerhead turtle feeds on the Portuguese man o' war, a common part of the loggerhead's diet.The turtle's skin is too thick for the sting to

penetrate. The sea slug Glaucus atlanticus also feeds on the Portuguese man o' war,as does the violet snail Janthina janthina. The blanket octopus is immune to the venom of the Portuguese man o' war; young individuals carry broken man o' war tentacles, presumably

for offensive and/or defensive purposes Fire Coral Fire corals are colonial marine organisms that look rather like real coral.

Fire corals have a bright yellow-green and brown skeletal covering and are widely distributed in tropical and subtropical waters. They appear in small brush-like growths on rocks and coral.

Divers often mistake fire coral for seaweed, and accidental contact is common. Upon contact, an intense pain can be felt that can last from two days to two weeks

Fire coral has several common growth forms, these include: branching Plate encrusting

Branching Branching adopts a calcareous structure which branches off, to

rounded fingerlike tips Plate Plate adopts a shape similar to that of the

smaller non-sheet lettuce corals; therefore erect, thin sheets, which group together to form a colony

encrusting, is where the fire coral forms on the calcareous structure of other coral Encrusting

Structure The polyps of fire corals are near microscopic size and are mostly embedded in the skeleton and connected by a network

of minute canals. All that is visible on the smooth surface are pores of two sizes: gastropores and dactylopores Dactylopores have long fine hairs that

protrude from the skeleton. The hairs possess clusters of stinging cells and capture prey, which is then engulfed by gastrozooids, or feeding polyps, situated within the gastropores Reproduction

Reproduction in fire corals is more complex than in other reef-building corals. The polyps reproduce asexually, producing jellyfish-like medusae, which are released into the water from special cup-like

structures known as ampullae. The medusae contain the reproductive organs that release eggs and sperm into the water. Fertilized eggs develop into freeswimming larvae that will eventually settle

on the substrate and form new colonies. Fire corals can also reproduce asexually by fragmentation Class Scyphozoa Jelly fish

Medusa form They are classified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles

Most jellyfish do not have specialized digestive, central nervous, respiratory, or circulatory systems.

The manubrium is a stalk-like structure hanging down from the center of the underside, with the mouth at its tip. The manubrim opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed.

It is joined to the radial canals which extend to the margin of the bell. Jellyfish do not need a respiratory system since their skin is thin enough that the body is oxygenated by diffusion.

They have limited control over movement, but can use their hydrostatic skeleton to navigate through contraction-pulsations of the bell-like body; some species actively swim most of the time, while others are

mostly passive. Depending on the species, the body contains between 95 and 98% water. Most of the umbrella mass is a gelatinous material (the jelly)called mesoglea which is surrounded by two layers of protective skin.

The top layer is called the epidermis, and the inner layer is referred to as gastrodermis, which lines the gut. Development The developmental

stages of scyphozoan jellyfish's life cycle: 13 Larva searches for site 48 Polyp grows 911 Polyp

1214 Medusa grows Jellyfish reproduce both sexually and asexually Sexual Reproduction

jellyfish spawn daily given enough food. In most species, spawning is controlled by light, so the entire population spawns at about the same time of day, (either dusk or dawn). Jellyfish are usually either male or female In most cases, adults release sperm and eggs

into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms. Asexual

After a growth interval, the polyp begins reproducing asexually by budding. Budding sites vary by species; from the

tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae Lifespan Jellyfish lifespans typically range from a few hours to several months. Life generally ends after the medusa has

begun spawning. Life span varies by species. Most large coastal jellyfish live 2 to 6 months, during which they grow from a millimeter or two to many centimeters in diameter.

Diet Jellies are carnivorous, feeding on plankton, crustaceans, fish eggs, small fish and other jellyfish, ingesting and voiding through the same hole in the middle of the bell. Jellies hunt passively using their tentacles

as drift nets Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom. Touching or being touched by a jellyfish can

be very uncomfortable, sometimes requiring medical assistance; sting effects range from no effect to extreme pain to death. Even beached and dying jellyfish can still sting when touched.

Class Cubozoa Box Jellies distinguished by their cube-shaped medusae The underside of the umbrella includes a flap, or velarium, concentrating and

increasing the flow of water expelled from the umbrella. As a result, box jellyfish can move more rapidly than other jellyfish. Box jellies

are known for the extremely potent venom produced by some species. Chironex fleckeri, Carukia barnesi and Malo kingi are among the most venomous creatures in the world . Stings from these and a few other species in the class are extremely painful and

sometimes fatal to humans. The box jellyfish actively hunts its prey ( zooplankton and small fish), rather than drifting as do true jellyfish. Each tentacle has about 500,000 cnidocytes

, containing nematocysts, a harpoon-shaped microscopic mechanism that injects venom into the victim. Many different kinds of nematocysts are found in cubozoans

Although the box jellyfish has been called "the world's most venomous creature",only a few species in the class have been confirmed to be involved in human deaths, and some species pose no serious threat at all.

In Australia, fatalities are most often perpetrated by the largest species of this class of jellyfish Chironex fleckeri. Class Anthozoa

Corals Sea Anemone

Largest class Only exist as polyps

They retain their nematocysts, or stinging cells, and may feed on large prey or particulate food, a number of them supplement their diet by growing symbiotic algae in their tissues

Sea anemones polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column-shaped body ending in an oral disc. Most are from 1.8 to 3 centimeters in

diameter, but anemones as small as 4 millimeters or as large as nearly 2 meters are known. They can have anywhere from a few tens to a few hundred tentacles

The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed. The venom is a mix of toxins, including neurotoxins, that paralyzes the prey so the anemone can move it to the mouth for digestion inside the gastrovascular cavity.

Both sexual and asexual reproduction can occur. In sexual reproduction males release sperm to stimulate females to release eggs, and fertilization occurs. Anemones eject eggs

and sperm through the mouth. The fertilized egg develops into a planula, which settles and grows into a single polyp.

Anemones can also reproduce asexually, by budding, binary fission (the polyp separates into two halves), and pedal laceration, in which small pieces of the pedal disc break off and regenerate into small anemones. coral

Most coral polyps live in colonies called reefs. Each polyp secretes a tough, stonelike outer skeleton of calcium carbonate that is cemented to the skeletons of its neighbors. Over thousands of years, these formations build up into coral reefs where hundreds of

thousands of polyps live together on top of old skeletons. Although some corals can catch small fish and plankton, using stinging cells on their

tentacles, like those in sea anemone and jellyfish, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular algae that live within the coral's tissue called zooxanthella

The polyps interconnect by a complex and well-developed system of gastrovascular canals, allowing significant sharing of nutrients and symbiotes.

Corals predominantly reproduce sexually. About 25% of hermatypic corals (stony corals) form single sex (gonochoristic) colonies, while the rest are hermaphroditic. Sexual

About 75% of all hermatypic corals "broadcast spawn" by releasing gametes eggs and sperminto the water to spread offspring. The gametes fuse during fertilization to form a microscopic larva called a planula. all corals spawn on the same night

Asexual Budding involves splitting a smaller polyp from an adult. Budding can be: Intratentacularfrom its oral discs,

producing same-sized polyps within the ring of tentacles Extratentacularfrom its base, producing a smaller polyp Types of Coral Reefs

Atoll Reef- extends all around a lagoon without a central island * when an island sinks below the oceans surface

Fringing Reef- directly attached to shore * grow up to the edge of the shore Barrier

Reef- separated from mainland by lagoon * only grow when there is a change of sea level on the coast adjacent from it * grow where land is sinking faster in the water

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