Phylum Cnidaria• A. Gr. knide – nettle) + L. aria, -like• 9,000 species.• Odd name = ph. Coelenterata, early 1900's •     coelenterate = Cnidaria + Ctenophora • Metazoans, have tissue but organs poorly defined • Tentacles present, can be fused • Mouth(=anus), digestive area = gastro-vasula cavity(GV) • Body can have covering skeleton, 98% of body is • Diploblastic ; 2 tissue layers(=ectoderm & endoderm) during

gastrula stage • In marine & fresh water

Phylum Cnidaria

-Body with 3 layers:epidermisgastrodermismesoglea (acellular)

-Gastrovascular cavity or coelenteron(often branched or divided with septa)

= with a single opening that serves as mouth and anus

Morphology and Digestion

• Radial or Biradial symmetry• Gastrovascular cavity• Most small; colonial organisms may be the most

massive on Earth• Tissue level of organization, a few organs• Extracellular digestion in gastrovascular cavity

intracellular in gastrodermal cells

Two basic forms: • Polyps

– Or hydroid form– Adapted to a sedentary

or sessile life

• Medusae– Or jellyfish form – Adapted for a floating or

free-swimming existence

• Polyps– Have tubular bodies– Mouth surrounded by tentacles (defines the oral

end)– Mouth leads into a blind gut or gastrovascular

cavity– Aboral end is usually attached to asubstratum by a

pedal disc or other device

Reproduce asexually by:› Budding› Fission› Pedal laceration

Zooids- buds that remains attached to the polyp:

•gastrozooids (for feeding)•dactylozooids (for defense)•gonozooids (for making sexually reproducing stages)

• Usually free-swimming• Have bell-shaped or umbrella-shaped bodies • Tetramerous symmetry (body parts arranged in fours)• Mouth is usually centered on the concave side • Tentacles extend from the rim of the umbrella

Jellylike layer of mesoglia is thicker – consisting the bulk of the animal and making it more buoyant medusae are commonly called jellyfishes

Medusae

Cnidaria – Excretion, Nervous System & Locomotion

• Simple excretion• Simple respiration by diffusion• Nerve cells and nerve net• Sense organs (statocysts and ocelli)• Some can swim by jet propulsion or through

cilia• Polymorphism in some species - medusa and

polyp

Skeleton and Reproduction

• hydroskeleton o exoskeleton or endoskeleton

• Reproduction can be sexual or asexual1. Asexual reproduction by budding

in polyps2. Sexual reproduction by gametes in

all medusae, some polyps3. Sexual forms monecious or

dioecious4. Planula larvae

Reproduction

• Hydra– Warm: Asexual (budding)– Dropping Temp triggers sexual

• Jellyfish– Polyps are asexual– Medusa are sexual

• Hermaphrodite– Anemone, mostly– Produce both egg and sperm

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Reproduction

• Individual Jellyfish are either male or female. The eggs and sperm develop in very colourful special areas called 'Gonads' inside the body wall. When all of the eggs and sperm are fully developed, they are released into the stomach and then through the mouth into the sea. In most cases, to reproduce, a male jellyfish releases his sperm into the surrounding water. The sperm then swims into the mouth of the female jellyfish, allowing the fertilization of the ova process to begin. Moon jellies, however, use a different process: their eggs become lodged in pits on the oral arms, which form a temporary brood chamber to accommodate fertilization.

Reproduction

• When the eggs are released into the sea they are fertilized by the sperm and continue to develop. As in all many-celled animals, the microscopic fertilized eggs begin a series of cell divisions which finally result in an embryo. However, the embryo does not develop directly into a baby jellyfish, but becomes a tiny, flattened creature called a 'Planula'.

• The Planula, which is covered with rapidly beating hairlike cilia (thin, tail-like projections), is able to swim and may be carried a considerable distance by ocean currents during its short swimming period, lasting from a few hours to several days. The tiny Planula then makes its way toward the sea bottom where it actively looks for a suitable place to attach itself. At this point, a amazing series of events take place.

Reproduction• The tiny Planula floating

in the sea.• Searching for a place to

attach itself.• Once attached, it feeds

on passing, floating food.

• At this stage, the Polyps mouth and tentacles are facing upwards.

• Grooves appear and become deeper, eventually cutting through the Polyps body.

• A pile of disc-shaped structures emerge and break away. Each being a baby Jellyfish.

• At this stage it is called a Medusa and is the Jellyfish form we recognise in our oceans.

Cnidaria - Ecology

– Mostly marine, some freshwater– Mostly freeliving– Feed by capture of prey; endosymbionts

Cnidocytes - stinging cells containing

nematocysts

• Nutrition: sting prey with nematocysts, push food into mouth with tentacles.

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Body Structure

a. Solitary

-forms remain as one polyp and one corallite. Colonial forms can reproduce the polyp asexually (cloning) and the new polyp forms another corallite that is attached to the first corallite. These colonial forms may have a general growth pattern that is somewhat horizontal, across a surface, like in the mounding or plate-like forms.

b. Colonial

-forms may grow vertically, branching like a tree. Each species of coral has its own polyp size (some tiny - less than a quarter of an inch, and some large - over a foot) and, if colonial, its own growth pattern.

The freshwater hydra is a simple organism with a basal

suction disk or foot, and apical tentacles.

• Nematocyst

Evolution and Taxonomy

– Cnidarians from ancestral radially symmetrical planula larva

– 4 Classes:o Anthozoa – sea anemones and corals (polyps; no medusa

stage)

o Hydrozoa – fire corals, Portuguese man-of-war, hydras

o Scyphozoa – jellyfish – medusa form is dominant but may begin as polyp

o Cubozoa – box jellyfish & sea wasp

Class Hydrozoa

– Gr. Hydra - water serpent + zoon, animal

– Dominated (in most) by the polyp form

– Mostly marine, mostly colonial– 2,700 species– Fresh water members of this class

live singly, but the marine forms live singly or form polymorphic colony.

– Though only polyp or medusa is found but sometimes both polyp or medusa may be found in the same animal.

– Gastrovascular cavity is directly connected with mouth.

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• Alternation of generation is found in the life cycle.

• Ciliated planula larva is found.• No stomodeum, velum present in

medusa.• Radial canals in medusa are not

branched.• Gametes develop from ectoderm

Kingdom Animalia  › Phylum Cnidaria 

Class Hydrozoa   Order Hydroida 

Suborder Hydrida  » Family Hydridae  

» Genus Hydra

Freshwater species Hydranths lack a chitinous covering With no medusa stage Length up to 25-30 mm

Hydra

• ZOOIDS• Mostly

HYDRANTHS (Gastrozooids – feeding polyp

• STALK

• BASE (basal disc or pedal)

Obelia• Class Hydrozoa

– Order Hydroida• Suborder Leptomedusae

Colonial or solitary Colonial marine hydroid that forms a minute

plantlike growth on rocks, pilings, and other substrates

Hydranths with chitinous covering

• Dioecious• Gametes are fertilized in the water and the

zygote develops into a planula larva which settles into substrate and metamorphose into colony

Class Scyphozoa

-Gr. skyphos, cup + zoon, animal dominated (in most) by the medusa form polyp (strobila) form free-swimming medusa

Some(Cassiopeia) with endosymbionts

200 species This Class contains the larger jellyfishes, with some

reaching two metres across the bell and with tentacles 30 metres long.

They are mainly marine and free floating, though they can "swim" by pulsations of the bell. In this Class the polyp stage is either reduced or absent. There are around 215 species.

Cassiopeia, the upside-down jellyfish, harbors endosymbionts which photosynthesize. Laying

upside-down in sunny areas brings light to the endosymbionts.

Class Cubozoa• Figure 13-20 (266)

• Gr. Kybos, cube + zoon, animal

• dominated (in most) by the medusa form

• about 100 species

• The cubozoan body is shaped like a square bell, with the mouth suspended inside it on a tube (the manubrium) that leads upward to the stomach, which is inside the top part of the bell. Extending around the inside bottom of the bell is a ring of tissue called the velarium, and at the bottom corners of the bell are muscular fleshy pads (pedalia), with one or more tentacles connected to each pedalium. Four sensory structures called rhopalia are located near the center of each of the four sides of the bell. Box jellyfish have eyes that are surprisingly complex, including regions with lenses, corneas, and retinas; however, box jellyfish do not have a brain, so how the images are interpreted remains unknown. Like all cnidarians, box jellyfish possess stinging cells that can fire a barb and transfer venom (Waggoner and Collins 2000).

Cubozoans are agile and active swimmers, unlike the more planktonic jellyfish. They have been commonly observed to swim a meter in just five to ten seconds, and there are unconfirmed reports of large specimens of Chironex fleckeri swimming as fast as two meters in one second (Waggoner and Collins 2000). The high speeds are achieved through a kind of squirting action in which the medusa contracts while the velarium at the bottom contracts even more, producing a constricted opening through which the water is forcefully expelled.

Box jellies can be found in many tropical areas, including near Australia, the Philippines, Hawaii, and Vietnam.

Class Anthozoa• Gr. Anthos, flower, zoon, animal• all polyps - no medusae• all marine• 6000 Species• Anthozoans include corals, sea anemones, sea pens,

and sea pansies.

- These animals are either solitary or colonial polyps that live attached to a substrate (surface).

- Of the 6,000 known anthozoan species, corals comprise about 2,500 species.

3 main groups of anthozoans:

(1) Sea anemones and hard corals

(2) tube anemones and thorny corals

(3) soft corals, horny corals, sea fans, sea

pens, sea pansies

• Sea anemones and corals have polyps and no medusae

• Corals are colonial and secrete calcium carbonate skeletons. Coral reefs are the accumulation of these skeletons.

• The sea anemone is considered to be the flower of the sea. Sea anemones look like plants, but they are really meat-eating animals.

• Sea anemones come in different sizes and many different colors.The sea anemone can attach itself to rocks or coral. In the center of the sea anemone is their mouth. In order for the sea anemone to eat, they must wait for their food to swim by. Then they sting it with their tentacles, and then push it into their mouth.

• Sea anemones spend most of their lives in one place. They can attach themselves to rocks. Some even bury themselves in the mud.

Anenomes are exclusively marine, as are all anthozoans.

Clownfish often live among the tentacles of the anenome. The clownfish are not stung by the anenome, and may help bring food to it. In return, the fish is protected by the stinging tentacles.

Rather than stinging, sun anenomes stick to their prey.

It is obvious as to how brain coral got its name.

Here is a young brain coral. These colonies

can build for thousands of years.

Other organisms, such as these Christmas Tree worms, make theur home in or on the coral.

Corals compete for light just the way plants do on land.

This is Elkhorn Coral.

Here a damselfish hides among the branches of fire coral. Fire coral has tiny spines which irritate the skin, much as a stinging nettle

does.

Soft corals such as dead-man’s fingers can bend with waves and

currents.

This is another soft coral.

Sea fans are also anthozoans along with sea anenomes, hard corals, tube anenomes, thorny corals, soft corals, sea pens

and sea pansies.

Specimen Class Colonial or Solitary Dominant stage

1. Hydra Hydrozoa Solitary Polyp

1. Obelia Hydrozoa Colonial Polyp and Medusa

1. Heliopora coerulea

Anthozoa Colonial Polyp

1. Montastrea curta Anthozoa Colonial Polyp

1. Oulastrea alta Anthozoa Colonial Polyp

1. Platygyra daedalea

Anthozoa Colonial Polyp

1. Mastigias papua Scyphozoa Solitary Medusa

1. Heterractis sp. Anthozoa Colonial Polyp

1. Fungia sp. Anthozoa Colonial Polyp

1. Galaxea fascicularis

Anthozoa Colonial Polyp

Heliopora coerulea

Pocillopora

Montastrea curtaPlatygyra daedalea

Trachyllia lekandia

Galaxea fascicularis

Porites

Goniopora undulata

Trachyphyllia lelandi

Herpolitha sp.

Galaxea fascicularisFavia stelligera

Platygyra sp.

Favia sp.

Fungia sp.Favites of halichora

Mastigias papua

Cryptodendrum adhesivumMastigias sp.