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CNIDARIA
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CNIDARIA
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Although many people are aware of corals, many do not realize that coral reefs are important not only to present day ecology but also in the geological past as major areas of oil formation. Coral reefs are a dominant feature of shallow tropical saline waters (at least 23.5 degrees centigrade). The northern and southern extend of present coral reefs define the extreme boundaries of the tropics. Cold water is not suitable for the formation of larger reefs, although some solitary corals can live in colder water. The Indo-Pacific region has the most diverse coral population that include over 700 species. In the tropical Atlantic there are only 35 species and are concentrated in the Caribbean area.
BIOLOGY. The characteristics of Cnidarians include the possession of radial symmetry, a sac-like body with a central body cavity, a body wall containing three basic cell layers, a single opening that acts as a mouth and anus and surrounded by food capturing tentacles, and possess stinging cells (nematocysts) situated on the tentacles. Cnidarians can be one of two forms a polyp (stationary) or a medusa (capable of movement). If you took your hands, palm down and opened and closed your fingers, that would represent a medusa. In this analog, the fingers would be the tentacles. If you placed your hand palm up and repeated the same motion this would represent a polyp or stationary formed (your arm would be attached to the substrate). In the figures below these two forms are illustrated.
The skeleton that corals make allows the polyp to retreat its
tentacles into the protection of its skeletons. Corals are suspension feeders.
The polyp has its tentacles out waiting for debris (goodies that fall in the
water column). When a tidbit hits its tentacles the polyp brings the food toward
the stomach where it is digested (raptorial feeding). The feeding mechanisms of
different reef coral species may vary in their retrieving this particulate
animal matter. Corals are stationary so they have developed different strategies
for protection and feeding. Corals can be solitary or colonial (more than one).
Massive colonial corals have individual polyps that range in size from 1-3 mm in
diameter, the solitary corals can reach up to 25 cm in diameter. Most people
think of corals as big massive structures, but few realize that these structures
are really a colony of the same species who have built a common skeleton.
Because calcium carbonate is more abundant in warm water, corals tend to build
larger structures in warm water. Corals in colder water tend to be smaller and
solitary. The Pacific coast has small solitary corals that are bright orange
which are commonly mistaken for sea anemones. The shape of the skeleton varies
from encrusting, spherical masses, to upright and branching growth forms. CLASSIFICATION. There are basically three taxonomic types of living corals: the cerianthipathanians (including black and thorny corals), hexacorallians (including stony corals), and octocorallians (including pipe and blue corals). In the geologic past, there have been many forms of coral that have become extinct. The cerianthipatharians have simple unbranched tentacles. Many of these corals have the fleshy part of the organism on the outside of the skeleton. Included in this group is the black coral, used in jewelry making. The hexacorallians are a diverse group with over 5300 living species. The group grows septa (supporting "bars" where the organisms "sits") in multiples of six, hence the derivation of "hexa." Included in this group are sea anemones and the scleractinia or stony corals. The stony corals are very common reef builders because they make a robust and white skeleton that tends to be massive. Also included are the brain, lettuce, and mushroom corals, The skeleton is composed of calcium carbonate and is secreted at the base of the polyp. The base contains radiating calcareous septa that help give the polyp support. The skeleton provides a substrate on which the polyp attaches with its fellow corals and protection against fish which like the tender corals for a snack. The octocorallian corals possess 8 tentacles that are pennate (looking like a feather). The skeleton is made of calcium carbonate and/or a horny (organic) material. The calcium carbonate however is not massive like in the stony coral and therefore not as robust. The octocorallian include the sea pens, sea fans, red coral, sea pansies, and pipe corals. This group tends to be more colorful in shades of red, blue, yellow, and brown. ECOLOGY. The ecology of living corals can be divided into two clearly defined groups, reef or hermatypic corals distinguished by symbiotic dinoflagellates and ahermatypic or "deep sea" corals which have no symbionts. Biologists have determined that there are certain limiting factors that influence the success of coral growth which include food, water movement, depth and illumination, temperature, salinity, sediment and substratum, and duration of the coral's larval stage. The growth of hermatypic corals adjusts to the water movement. Delicate, branching, and unattached colonies are unsuited to rough-water and are more characteristic of deeper water. Massive, encrusting, and stout colonies are capable of withstanding strong wave and current actions and are common on reef margins and exposed areas. Some species only live in certain niches, but there are other species that can change form, depending where they "live" (this is called plasticity of form). For example there have been many studies on the genus Acopora and its structure form in different water depths. In deep water Acropora are tall, branching, and erect; intermediate colonies are stouter with polyps in cone-like crest; in shallow water the colony is massive and very stocky. Growth form of the ahermatypic corals does not vary as much as hermatypic corals. The growth form is either small encrusting or massive colonies. The largest colonies are dendroid, and differ from hermatypic by having the individual polyps spaced farther apart. Solitary forms display a wide range of forms and adapted to various kinds of bottoms. FOSSIL CORALS. Living corals today are only a small portion of the different corals that lived throughout geologic time. Evidence for these corals can be seen in the interior of North America (especially in the southwest states), when a shallow, warm sea covered the area in the Paleozoic times. Many Americans know that Texas is a major produce of oil and are familiar with the beauty of the Carlsbad Caverns in New Mexico, but few realize that this area was one of the largest carbonate reef build-ups in the world during the end of the Paleozoic. The Guadalupe Mountains at one time the site of a reef that encircled the area of Texas and New Mexico. The ancient reef provided the organic material to produce the oil and the fossil reef provides the caves and porous rock to hold the oil. The Rugosa corals are now extinct ranging from the Cambrian to the Late Triassic. They were mostly solitary differing from the stony corals because its septa are in multiples of four (hence their other name and the tetracorals). Rugosa corals evolved from solitary (simple cup) horn-of-plenty looking coral, to branching individuals and then to massive colonial that lacked walls when the Rugosa corals went extinct. The subclass Tabulata, a colonial coral went extinct at the end of the Permian. They had a heavy calcareous skeletonal, with parallel tubes and horizontal platforms. The little organism did not have septa, so the platform or tabula acted as a base. INTERPRETING CORALS. Fossil coral reefs are interpreted by geologists, as representing warm, shallow, and clear water. The reef environment is ideal for many chemical reactions to take place, including increase of temperature, intense evaporation, influx of supersaturated water where calcium carbonate nuclei or other catalysts are present, upwelling, mixing of water, bacterial decay, rising pH , and removal of carbon dioxide by photosynthesis. These chemical reactions are all favorable for oil formation. Geologist can identify the different types of corals, which help them to interpret the environment of deposition. corals are awesome reef builders that are biologically and geological important. Biologically, corals provide the backdrop to a dynamic living community. Geologically, reefs turn into large carbonate deposits which means that there was organic matter to produce oil and enough porosity or holes in a ancient reef to keep or act as a reservoir for oil.
COMPARING CORALS - LAB Corals belong to the Class
Anthozoa within the Phylum
Cnidaria, which include hydroids, jellyfish, and sea anemones.
In many textbooks they are put in the phylum "coelenterate"
but many biologists feel that this term refers to the cnidarians and
ctenephores. Cnidarians have
stinging cells and ctenophores or the "comb jelly" do not.
The characteristics of Cnidarians include the possession of radial symmetry, a sac-like body with a central body cavity, a body wall containing three basic cell layers, a single opening that acts as a mouth and anus and surrounded by food capturing tentacles, and possess stinging cells (nematocysts) situated on the tentacles. Cnidarians can be one of two forms a polyp (stationary) or a medusa (capable of movement). If you took your hands, palm down and opened and closed your fingers, that would represent a medusa. In this analog, the fingers would be the tentacles. If you placed your hand palm up and repeated the same motion this would represent a polyp or stationary formed (your arm would be attached to the substrate). In figures below the two forms are illustrated. The skeleton that corals make
allows the polyp to retreat its tentacles into the protection of its
skeletons. Corals are suspension
feeders. The polyp has its tentacles out waiting for debris (goodies that fall
in the water column). When
a tidbit hits its tentacles the polyp brings the food toward the stomach where
it is digested (raptorial feeding). The
feeding mechanisms of different reef coral species may vary in their
retrieving this particulate animal matter.
Corals are stationary so they have developed different strategies for
protection and feeding.
Corals can be solitary or colonial (more than one).
Massive colonial corals have individual polyps that range in size from
1-3 mm in diameter, the solitary corals can reach up to 25 cm in diameter.
Most people think of corals as big massive structures, but few realize
that these structures are really a colony of the same species who have built a
common skeleton.
Because calcium carbonate is more abundant in warm water, corals tend
to build larger structures in warm water.
Corals in colder water tend to be smaller and solitary.
The Pacific coast has small solitary corals that are bright orange
which are commonly mistaken for sea anemones. The shape of the skeleton varies
from encrusting, spherical masses, to upright and branching growth forms.
There are basically three taxonomic types of living corals:
the cerianthipathanians (including black and thorny corals),
hexacorallians (including stony corals), and octocorallians (including pipe
and blue corals). In the geologic
past, there have been many forms of coral that have become extinct.
The cerianthipatharians have simple unbranched tentacles. Many of these corals have the fleshy part of the organism on
the outside of the skeleton. Included
in this group is the black coral, used in jewelry making.
The hexacorallians are a diverse group with over 5300 living species.
The group grows septa (supporting "bars" where the organisms
"sits") in multiples of six, hence the derivation of "hexa."
Included in this group are sea anemones and the scleractinia or stony
corals. The stony corals are very common reef builders because they make a robust and white skeleton that tends to be massive. Also included are the brain, lettuce, and mushroom corals, The skeleton is composed of calcium carbonate and is secreted at the base of the polyp. The base contains radiating calcareous septa that help give the polyp support. The skeleton provides a substrate on which the polyp attaches with its fellow corals and protection against fish which like the tender corals for a snack. The octocorallian corals
possess 8 tentacles that are pennate (looking like a feather). The skeleton is made of calcium carbonate and/or a horny
(organic) material. The calcium
carbonate however is not massive like in the stony coral and therefore not as
robust. The octocorallian include
the sea pens, sea fans, red coral, sea pansies, and pipe corals.
This group tends to be more colorful in shades of red, blue, yellow,
and brown.
The ecology of living corals can be divided into two clearly defined
groups, reef or hermatypic corals distinguished by symbiotic dinoflagellates
and ahermatypic or "deep sea" corals which have no symbionts.
Biologists have determined that there are certain limiting factors that
influence the success of coral growth which include food, water movement, depth and
illumination, temperature, salinity, sediment and substratum, and duration of
the coral's larval stage.
The growth of hermatypic corals adjusts to the water movement.
Delicate, branching, and unattached colonies are unsuited to
rough-water and are more characteristic of deeper water.
Massive, encrusting, and stout colonies are capable of withstanding
strong wave and current actions and are common on reef margins and exposed
areas. Some species only live in
certain niches, but there are other species that can change form, depending
where they "live" (this is called plasticity of form).
For example there have been many studies on the genus
Acopora and its structure form in different water depths.
In deep water Acropora are
tall, branching, and erect; intermediate colonies are
stouter with polyps in cone-like crest; in shallow water the colony is massive
and very stocky. Growth form of the ahermatypic corals does not vary as much as hermatypic corals. The growth form is either small encrusting or massive colonies. The largest colonies are dendroid, and differ from hermatypic by having the individual polyps spaced farther apart. Solitary forms display a wide range of forms and adapted to various kinds of bottoms. ANTHOZOA The
following are specimens that students will look at.
Have them rotate specimens, so all students can view them. CLASS ALCYONARIA = Octocorals
BLUE CORAL - Helipora species (blue colored specimen)
This Indo-Pacific blue coral, Heliopora, is relatively rare.
It has a massive lobed skeleton dissected
by cylindrical canals. The blue
tint of the skeleton is masked in life by the brown
polyps, and is due to the presence of iron salts.
It is used in jewelry because of its color.
BLACK SEA FANS
- Order Gorgonacea (black delicate fan structure)
The main stem is firmly attached to a hard surface by a plate or a tuft
of creeping branches.
The stems contain a central strengthening rod, consisting of a horny
material (gorgonin). The short polyps occur all over the branches of the colony
being absent only on the main stem.
RED ORGAN PIPE CORAL - Tubipora
sp. (red specimen)
The common name is derived from the parallel rows of tubes making up
the calcareous skeleton of the
colony. When the polyps are
expanded, the red skeleton may be completely obscured. Colonies can reach 30
cm or more in diameter. Found in
the Indo-Pacific. CLASS ZOANTHARIA = Hexacorals
STAGHORN CORAL - Acorpora species (white, long straight specimen)
Another of the fast growing reef builders, staghorn coral forms
thickets, sometimes of great
size, with a lattice-work of loosely connected branching coral colonies.
Colonies may be yellow, brown or cream color with white tips (where the
growth takes place). Staghorn thickets are found not often seaward of the reef
flat, where they may adorn the tops of buttresses at moderate depths.
They are also found forming patch reefs in protected
lagoons and shore zones in shallow water connected to other colonies
(if at all), and are encrusted with algae, sponges, and tunicates.
Damselfishes frequently stake out their territories in staghorn as well
as elkhorn coral.
ELKHORN CORAL - Acorpora species (creamy white, smoother specimen that looks like a
reindeer's horn) The fast growing branching
colonies of this coral are sometimes 4 meters or more across The flattened (or
thick and cylindrical) branches are brown to yellow with white tips (due
to the lack of symbiotic algae, the zooxanthellae, in these areas of
new growth).
Elkhorn coral competes by growing rapidly and by shading or
over-topping its neighbors. It
often dominates shallow fore reef zones on windward, wave-swept shores. It is sometimes toppled by storm surf, but may re-grow from
its new positions (broken
fragments regenerate to form new colonies) capability which may partially
explain its wide distribution
BRANCHING, BRUSH, OR BROWN STEM
CORAL - Madracis (specimen with
brown spots with branching tips)
These yellow to cream-colored colonies may be several meters across and
are formed of thin delicate
branches packed tightly together. The
more massive colonies form gently rounded
mounts.
This coral is found at moderate depths on buttress tops, flanks, and
fore reef slopes. Brittle
stars and other invertebrates are often harbored between the branches.
Inner parts of the branches
are dead and are encrusted with algae, sponges, and other attached
invertebrates. The brittle
branches of the coral are easily damaged by divers and
boat anchors.
POCA CORAL - Montipora
species white, small polyps, crinkled, some have small red
specks on them. Poca
forms flat, leafy colonies which may reach 2 meters or more across. It often grows in
dense masses over reef slopes in the Indo-Pacific.
MUSHROOM CORAL - Fungia
species (individual polyp, circular specimen with large
septa)
A common species reaching 20 cm in diameter, which is found on reefs
and lagoons in the Indo-Pacific.
As adults, all species are free-living, but when young they are often
seen in clumps, each polyp
attached to the bottom by a stalk.
CUP CORAL - Turbinaria
teltata
A normally dome shaped colonial coral which grows to over 30 cm in
diameter. The colony is cup
shaped when viewed with the underside uppermost.
found on reefs and adjacent sand in the Indo-Pacific.
FLOWER CORAL - Eusmilia species (white, large polyps that give the appearance of
being squished)
The branching colonies of this coral are brown, green, or yellow and
have one large polyp at the top
of each branch. Colonies form
mounds which may be 1 meter or more across. The polyps are generally retracted
during the day, but extend long transparent tentacles for feeding on plankton
at night.
LEAF CORAL - Montipora species (slightly green , small holes, flatten)
Leaf corals form flat, leafy colonies which may reach 2 meters or more
across. They often
grow in dense masses over reef slopes in the Indo-Pacific.
DOTTED LINE CORAL - Agaricia
species. The white star shaped
dos which run in grooves are conspicuous and mark the location of the polyps.
These colonies form flat, encrusting plates and are tan to brown.
This coral overgrows and encrust large areas of the reef in moderately
deep marine areas of the reef. Answers to Lab Sheet CNIDARIA
II 1.
Blue coral: this coral is
blue. It has a flat shape and has
many obvious pores. It is light
to heavy in weight and has sharp edges. 2.
Black Sea Fan: this coral
looks like a tree branch or twig. It
is brown to black in color and is brittle.
The pores are small and somewhat hard to see. 3.
Red Pipe Organ: this coral
is dark red in color. The
chambers that make up the living spaces of the polyps are tubular or
“pipe” in shape. The mass of
the coral is long and thick and is built upward from the base. 4.
Dotted-line: this coral is
flat in shape and has definite “chambers” for polyp pores.
It is white to light yellow in color and has small ridges in rows. 5.
Staghorn: this coral is long
with medium to small pores. It is
very sharp and brittle. It has a
branching and thick look. 6.
Elkhorn: this coral is
branching with thick obvious polyp chambers.
There are larger holes at the tips of the branches.
It is white to cream in color. 7.
Brown stem: this coral is
white with patches of brown color. It
has a branching shape and lots of pores everywhere. 8.
Poca: this coral is flat and
thin with small pores. It is
yellow in color and has small ridges along both sides. 9.
Mushroom: this coral is flat
with raised sharp gills. It is
very white in color and has a flat base for the bottom. It looks a little like a sand dollar. 10.
Flower: this coral looks
like a scallop. It has sharp gill
slits sandwhiched in between the fold. It
is brown to whitish in color. 11.
Cup: this coral is very
spiny and sharp. It has many
ridges and is white to yellow in color. 12. Leaf: this coral is a little thicker than the poca coral. It is flat with large pores. It is yellow to white in color.
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This
is from Coral Kit..... look at other material and merge
Corals
belong to the Class Anthozoa within the Phylum Cnidaria, which include
hydroids, jellyfish, and sea anemones. In many textbooks they are put in the
phylum "coelenterate" but many biologists feel that this term refers
to the cnidarians and ctenophores. Cnidarians have stinging cells and
ctenophores or the "comb jelly" do not.
