Phylum Cnidaria Hydras jellyfish sea anemones and corals

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- medusa alternates between polyp and

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 free-swimming. • 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 free-swimming 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 umbrellashaped 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 belllike 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: 1– 3 Larva searches for site 4– 8 Polyp grows 9– 11 Polyp 12– 14 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 � Only � They class exist as polyps 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 sperm—into 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: � Intratentacular—from its oral discs, producing same-sized polyps within the ring of tentacles � Extratentacular—from its base, producing a smaller polyp

Types of Coral Reefs v Atoll Reef- extends all around a lagoon without a central island * when an island sinks below the ocean’s surface

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

v 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