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28.2 The Simplest Invertebrates
Discuss how a sponge reproduces.
Compare the features of ctenophores to those of cnidarians.
The table summarizes the classification of organisms.
The most ancient and simplest animals are sponges, cnidarians, and ctenophores.
The only animals that lack true tissues are multicellular.
They don't have the nerve and muscle cells seen in more complex animals.
The body of a sponge is porous.
Sponges are mostly marine animals that vary in size, shape, and color.
They all have a canal system that allows water to move through their bodies.
Food particles in the water are trapped by the collar cells.
The amoebocytes transport vitamins and minerals from cell to cell.
Some sponges have internal skeletons.
The canals are lined with cells that look like choanoflagellates.
The cells in a sponge are called collar cells.
The beating of the flagella causes water currents to flow through the central cavity and out through the osculum.
A 10 cm sponge is enough to filter 100 liters of water a day.
The sponge's cells are able to get the oxygen they need from the water.
A suspension feeder is a sponge that filters suspended particles from the water by means of a straining device.
The food particles that pass between the microvilli are engulfed by the collar cells and eaten.
The body is protected from collapsing by the skeleton of a sponge.
The sponges are made from a modified form of collagen called spongin, and the bath sponges are made from a dried skeleton of it.
Sponges are usually synthetic.
Small, needle shaped structures called spicules are typically found in the sponge's endoskeleton.
The type of spicule has been used to classify sponges.
The success of sponges is due to their spicules.
A mouth full of spicules is an unpleasant experience.
Toxic substances are produced by some sponges.
Sponges can reproduce both sexually and asexually.
They reproduce asexually by fragmenting or budding.
A small protuberance appears and gradually increases in size until a complete organisms forms.
colonies of sponges can become large.
During sexual reproduction, eggs and sperm are released into the central cavity, and the zygote develops into a flagellated larva, which may swim to a new location.
sponges are capable of regrowth or growth of a whole from a small part.
If the cells of a sponge are mechanically separated, they will reassemble into a functioning organisms.
These two groups of animals have true tissues, and as embryos, they have two germ layers.
They are symmetrical as adults.
Ctenophora, or comb jellies, are usually found in warm waters.
Ctenophores are the largest of these animals and range in size from a few centimeters to 1.5 m in length.
Most ctenophores use sticky cells called colloblasts to capture their prey.
There is a difference between comb jelly and cnidarian.
Both animals have similar features.
Recent studies show that ctenophores have more ancient DNA than sponges.
There is still a lot of debate about their placement because of the uncertainty of the DNA evidence.
Some freshwater, brackish, and oceanic forms of the Cnidarian are known.
A fluid-filled capsule is called a (Gk.
Thebladder contains a long, spirally coiled, hollow thread.
The nematocyst is discharged when the cnidocyte is touched.
The body of a cnidarian has two layers.
The outer tissue layer is protective.
The inner tissue layer, which is derived from endoderm, is the source of the internal juices.
It functions in the digestion of food.
Flexibility is allowed by the fluidmuscle.
The two tissue layers are separated.
There are two basic body forms.
The medusa has more of a body than a polyp, and the tentacles are concentrated on the margin of the bell.
At one time, both body forms may have been a part of the life cycle of a cnidarian.
The motile medusan stage produces egg and sperm when both are present.
One stage is dominant and the other is reduced in some cnidarians.
The flower of the sea is called the sea anemone.
Corals are skeletons made of calcium carbonate.
The colony of modified polyps and medusae is called the Portuguese man-of-war.
Sea anemones are attached to submerged rocks, timbers, or other objects.
The sea anemones range in size from small to 10 cm in diameter and are often colorful.
Their oral disk Page contains the mouth and is surrounded by a large number of hollow tentacles.
Corals look like sea anemones in a house.
The coral can extend into the water and retreat into the house for safety.
Corals build coral reefs.
They have beautiful designs and colors.
Coral reefs are built from limestone.
The Great Barrier Reef along the eastern coast of Australia can be a result of hundreds of years of accumulating.
A diverse group of marine life call the coral reef home.
The hydrozoans have a dominant stage.
You might think the Portuguese man-of-war is an odd-shaped medusa, but it is actually a colony of polyps.
The gas-filled float keeps the colony afloat.
The bud from this one is specialized for feeding or reproduction.
A long, single tentacle armed with numerous nematocysts arises from the base of each feeding polyp.
Swimmers who come upon a Portuguese man-of-war can suffer serious injuries.
The buds become an animal.
There are two tissue layers in the body wall.
There are cells that contain nematocysts.
The medusa is the primary stage and the polyp is small.
Jellyfish depend on tides and currents for their primary means of movement.
An example of a cnidarian is hydras.
Most lakes and ponds have hydras attached to them.
The body of a hydra is a small tubular polyp about one-quarter of an inch in length.
The mouth and anus can be found in a raised area surrounded by a large number of nematocysts.
The cells of the skin contain muscles.
There are nematocyst- containing cnidocytes in the skin.
The body of a hydra can contract or extend, and the tentacles that ring the mouth can reach out and grasp prey and discharge nematocysts.
By forming buds, small outgrowths that develop into a complete animal and then detach, hydras reproduce asexually.
Interstitial cells can become other types of cells, such as an ovary and a testis.
When hydras reproduce sexually, sperm from a testis swim to an egg.
The embryo is encased in a protective shell that allows it to survive until it emerges and develops into a new polyp.
hydras can grow an entire organisms from a small piece, and cnidarians have great regeneration powers.
There are three ways in which cnidarians are more complex than sponges.
Define how a sponge gets its nutrition.
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