Download Lab 2: Phylum Cnidaria

Lab 2: Phylum Cnidaria
Name
: Wan Nursyuhada Bt Wan Mohd Rozihas
Matric No.
: A155843
Lecturer’s Name
: Dr. Wan Mohd Lotfi Bin Wan Muda
Date
:
1.0 – Introduction
The Cnidaria is a group of animals are well known to many people under their common
names, Sea Anemones, Corals and Jellyfish are all Cnidarians as are Hydras, Sea Whips, Sea
Fans and Sea Pansies. They are linked together by their carnivorous feeding habits their
simple anatomical design and the possession of nematocysts, though one species of
Ctenophora possesses nematocysts as well. The name Cnidaria has now pretty much replaced
the older term of Coelenterata which these days is often applied to both the Cnidaria and the
Ctenophora together, these two phyla are also known as the Radiate Animals because they
both have radial or biradial symmetry. The word Cnidaria refers to Cnidocysts, specialised
cells which contain the Nematocysts, the stinging organelles that allow the Cnidaria to
subdue their prey.
The Cnidaria are the oldest of the true metazoan phyla. A fossil Hydrozoan from South
Australia called Ediacara is 700 million years old, while numerous fossil Cnidarians exist
from the Cambrian 500 million years ago. The Cnidarians, particularly the corals often make
up an important component of the shallow marine fauna of tropical and subtropical seas. All
the Cnidaria are aquatic and nearly all are marine. Corals because of their shallow marine
environment and their habit of accumulating a mineralised skeleton (coralite) tend to fossilize
well and we know quite a bit about their evolution.
The Cnidarian body is basically a U shape with intact walls that surround a central digestive
area and a mouth at the opening, generally surrounded by tentacles, there is no distinct anus.
In Anemones the mouth faces up, and in Jellyfish it faces down. The Cnidarians show a more
complicated arrangement of cell layers as well as a greater range of cell types than the
Porifera. Their bodies show two distinct layers of cells and thus they are called 'Diploblastic
animals'. The two cell layers are an outer Epidermis or Ectoderm, and an inner Gastrodermis
or Endoderm. These two layers are separated by the mesoglea a non-cellular fibrous jelly like
material that is thin in some groups such as the Hydras but can be quite thick in other such as
the Jellyfish where it helps provide negative buoyancy (makes the animal more likely to
float). The ectodermis consists of five basic cell types, Epitheliomuscular cells which supply
some of the muscular capabilities of the animal, Interstitial cells which are basic cells that
give rise to the other cell types, Cnidocysts (see below), Mucous glands and sensory or nerve
cells. The endodermis consists of three or four basic cell types Gastromuscular cells which
help digest food items and provide some muscle power, Gland cells that secrete enzymes for
digestion, Mucous cells and in Anemones but not in Hydras, Cnidocytes.
One of the most important distinguishing characteristics of the phylum are the Nematocysts.
Nematocysts, and their enclosing Cnidocysts come in about 24 different forms, the
differences play a functional role in the classification of the phylum. A Cnidocyst is a cell
that secretes a nematocyst within it. A basic Nematocyst is a capsule made of something like
chitin within which rest a coiled thread. This thread can be shot out of the capsule to
encounter prey items, or in some cases to repel predators. The Cnidocyst has either a
modified flagellum called a Cnidocil, or a cone as a sensory trigger. If this trigger is touched
the nematocyst thread is rapidly ejected. Nematocyst threads come in 3 basic types. The
fundamental nematocyst is a thin tubular thread with barbs at the far end, though there may
be barbs near the base as well. When the nematocyst is discharged, the barbs penetrate the
skin of the prey and a toxin can be injected. Ptychocysts are uncommon, occurring only in the
Ceriantharians, they lack spines or barbs but are adhesive and can be used to line the tubes
the Ceriantharians live in as well as to entangle prey. Spirocysts also lack barbs or spines,
they are an enclosed tube that is adhesive, they are used to trap prey in a tangled net of sticky
threads.
The Cnidaria come in two basic forms, a 'Polyp' form typified by the Sea Anemones and a
'Medusa' form typified by Jellyfish. Generally speaking Polyps are tube shaped and sedentary
with a ring of tentacles around the mouth, Medusae are umbrella or bell shaped, free living
and have a central projection on the inside of the umbrella which supports the mouth and
their tentacles around the rim of the umbrella.
The Cnidarians are either carnivores or omnivorous filter feeders.The the carnivorous forms
do not hunt their prey, instead they use various 'sit and trap' or 'float/swim and trap' strategies,
using their Nematocysts, which are not only found on the stinging tentacles but can be all
over the animals body, to stun and or kill their prey. There are about 10, 000 species of
Cnidarians divided between 3 classes Hydrozoa, Scyphozoa and Anthozoa.
2.0 – Materials
-
Microscope
Slides
Cover slips
Dissecting set
Petri dish
Clorox
Rubber gloves
3.0 – Specimens
Hydrozoa
1. Obelia
2. Millipora (Fire coral)
Scyphozoa
1. Jellyfish (Moon jelly)
Anthozoa
1.
2.
3.
4.
5.
6.
7.
8.
9.
Sea Anemone
Fungia (Mushroom coral)
Acropora
Montipora
Pavona
Sea pen
Sea fan
Sea whip
Dendronephyta (Soft coral)
4.0 – Methodology
Observation of polyps and corallites:
1. In the lab, we were provided with specimens which were Hydrozoa, Scyphozoa and
Anthozoa.
2. For Hydrozoa, the specimens provided were Obelia and Millipora (fire coral). We
observed the polyps of the specimens under the microscope and made important
remarks about them.
3. For Scyphozoa, the specimen was jellyfish. Aurelia Aurita is the name of the jellyfish.
Its common name is Moon Jelly. After placing it on the petri dish, we observed its
gastric pouches, oral arms, mouth and tentacles.
4. The last one is Anthozoa. Under this class, there were many specimens provided and
were observed.
Extracting the spicules:
1. The soft coral was cut into a small piece and placed in a petri dish.
2. 5% of sodium hypochlorite solution (Clorox) was pipetted into the petri dish to
dissolve the soft coral.
3. The soft coral was left for it to dissolve for 20-30 minutes.
4. The spicules were pipetted and dropped onto glass slide and was covered with a cover
slip. The spicules were observed under a compound microscope.
5.0 – Results and Observation
1. Hydrozoa
A) Obelia (Obelia longissima)
The polyp is the asexual stage and the medusa the sexual stage. In such organisms the polyp,
by budding, gives rise to medusae, which either detach themselves and swim away or remain
permanently attached to the polyp. The medusae then produce new polyps by sexual
reproduction. A medusa produces eggs or sperm, which are usually shed into the water; when
an egg is fertilized, it develops into a swimming larva, which eventually settles and grows
into a polyp. In addition to this elaborate means of reproduction, the polyp can form new
polyps by budding. In some groups of coelenterates either the polyp or the medusa has
become highly developed, with the reduction or complete loss of the other form. During the
polyp stage, the mouth is situated at the top of the body, surrounded by tentacles. Its skeleton
is composed of chitin.
B) Millepora (Millepora alcicornis) – Fire coral
The skeleton of a fire coral is calcareous and is made up of Calcium Carbonate. Branching
adopts a calcerious structure which branches off, to rounded, finger-like tips.
The gonophores in the family Milleporidae arise from the coenosarc (the hollow living tubes
of the upright branching individuals of a colony) within chambers embedded entirely in the
coenosteum (the calcareous mass forming the skeleton of a compound coral).
Millepora and hard corals are different and Millepora cannot be classified as a hard coral
because their polyps are different. Polyp of Millepora does not have a pharynx or tentacles.
Its coralite too has no septa like those of in corals.
2. Scyphozoa
-
Jellyfish (Aurelia Aurita) – Moon jelly
Scyphozoans usually display a four-part symmetry and have an internal gelatinous material
called mesoglea, which provides the same structural integrity as a skeleton. The mesoglea
includes mobile amoeboid cells originating from the epidermis. Aurelia undergoes alternation of
generations, whereby the sexually-reproducing pelagic medusa stage is either male or female,
and the benthic polyp stage reproduces asexually. It feeds by collecting medusae, plankton,
and mollusks with its tentacles, and bringing them into its body for digestion. It is capable of only
limited motion, and drifts with the current, even when swimming.
3. Anthozoa
A) Sea Anemone (Metridium senile)
The base of Metridium senile is considerably wider than the column and is attached to rock or
another substrate. The column is long, smooth and cylindrical, of a fleshy consistency with a
slimy surface lubricated with mucus. There are no warts or suckers and the column is topped
by a parapet and deep groove. The oral disc is broad and deeply lobed into several curving
sections that overhang the column. The slender, pointed tentacles are very numerous in larger
specimens though fewer and relatively longer in smaller ones. Those near the margin are
crowded and short whereas further into the disc they are longer and more dispersed.
B) Fungia ( Fungia sp.) – Mushroom coral
Corals in the genus Fungia are mostly solitary, some attaining 30 centimetres in diameter.
However Fungia simplex is colonial. The juveniles attach themselves to rock but larger
individuals detach themselves and become free living. They are found in various bright
colours including white, pink, red, purple, blue and yellow and are popular with keepers
of reef aquariums. The discs are either round or oval and the central mouth, which is
surrounded by tentacles, may be a slit. The polypsits in a calcareous cup, the corallite.
The septa are vertical skeletal elements inside the corallite wall and the costae join the septae
and continue outside the corallite wall and underneath the coral.
C) Acropora (Acropora sp.)
Acropora is a genus of small polyp stony coral in the phylum Cnidaria. Some of
its species are known as table coral, elkhorn coral, and staghorn coral. Over 149 species are
described. Acropora species are some of the major reef corals responsible for building the
immense calcium carbonate substructure that supports the thin living skin of a reef.
Acropora species may grow as plates or slender or broad branches. Like other
corals, Acroporacorals are colonies of individual polyps, which are about 2 mm across and
share tissue and a nerve net.
The polyps can withdraw back into the coral in response to movement or disturbance by
potential predators, but when undisturbed, they protrude slightly. The polyps typically extend
further at night to help capture plankton and organic matter from the water. Acropora is most
common in shallow reef environments with bright light and moderate to high water motion.
Many small reef fishes live near their colonies and retreat into the thicket of branches if
threatened.
D) Montipora (Montipora sp.)
Montipora is a genus of small polyp stony coral in the phylum Cnidaria. Depending on the
species and location, Montipora may grow as plates or ridges, appearing to some as a bowl or
flower. Undisturbed, the plates expand radially and may encrust over surrounding rocks,
shells or debris. Members in this genus are usually thin corals that form leafy, plate-like,
encrusting or semi-massive colonies. The colours vary greatly. The calices are less than 2 mm
in diameter and are usually well separated by the coenosteum. The skeleton is lacy, the walls
are indistinct and the septa, when present are small and in 2 cycles. The columella is rarely
developed and the corallites are inconspicuous and appear empty as the polyps are very small.
E) Pavona (Pavona sp.)
Corals in this genus have a range of different forms including those that are massive,
meandering, columnar, leaf-like, and plate-like. A single species may vary in form according
to the current, wave action, lighting conditions, and depth of its location. Members of the
genus are distinguished from other corals by having no walls to thecorallites, but having
clearly delineated septocostae that connect each corallite to its neighbours, giving a flowerlike pattern on the surface of the coral. The corallites themselves are shallow depressions
with central columella and may be separated by ridges. The polyps are only extended at night.
The foliose and plate-like forms tend to be two-sided.
F) Sea Pen (Pteroides sp.)
Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 16
families within the order; they are thought to have a cosmopolitan distribution in tropical and
temperate waters worldwide. Sea pens are grouped with the octocoralia ("soft corals"),
together with sea whips or gorgonians.
Although named after their feather-like appearance reminiscent of antique quill pens, only
sea pen species belonging to the suborder Subselliflorae live up to the comparison. Those
belonging to the much larger suborder Sessiliflorae lack feathery structures and grow in clublike or radiating forms. The latter suborder includes what are commonly known as sea
pansies.
Sea pens are colonial animals with multiple polyps (which look somewhat like miniature sea
anemones), each with eight tentacles. Unlike other octocorals,
however, a sea
pen's polyps are specialized to specific functions: a single polyp develops into a rigid, erect
stalk (the rachis) and loses its tentacles, forming a bulbous "root" orpeduncle at its base.
G) Sea Fan (Gorgonia sp.)
The structure of a gorgonian colony varies. In the suborder Holaxonia, skeletons are formed
from a flexible, horny substance called gorgonin. The suborder Scleraxonia is one of the
varieties of gorgonians which is supported by a skeleton of tightly grouped calcareous
spicules. There are also species which encrust like coral.Most of Holaxonia and Sclerazonia,
however, do not attach themselves to a hard substrate. Instead, they anchor themselves in
mud or sand.
Research has shown that measurements of the gorgonin and calcite within several long-lived
species of gorgonians can be useful inpaleoclimatology andpaleoceanography, as the skeletal
growth rate and composition of these species is highly correlated with seasonal and climatic
variation.
H) Sea Whip (Sinularia sp.)
Colonies heavily branched, more or less in single planes; colonies up to 60 cm in height. Sea
whip has long, flexible, quite flat and wide branches which are tapered somewhat from the
base to the end. Polyps extend from a groove that runs along the thin edges. The color varies
from purple, white to cream. Sea whips inhabit a wide range of inshore environments, from
back reef areas of sand and rubble to patch reefs of moderate depth.
I) Dendronephyta (Dendronephyta sp.) – soft coral
Dendronephyta or soft corals, are an order of corals which do not producecalcium
carbonate skeletons. Soft corals contain minute, spiny skeletal elements called sclerites,
useful in species identification. Sclerites give these corals some degree of support and give
their flesh a spiky, grainy texture that deters predators.
Unlike stony corals, most soft corals thrive in nutrient-rich waters with less intense light.
Almost all utilize symbiotic photosynthesizing zooxanthella as a major energy source.
However, most will readily eat any free floating food, such as zooplankton, out of the water
column. They are integral members of the reef ecosystem and provide habitat for fish, snails,
algae and a diversity of other marine species.
Many soft corals are easily collected in the wild for the reef aquarium hobby, as small
cuttings are less prone to infection or damage during shipping than stony corals. Nevertheless,
home-grown specimens tend to be more adaptable to aquarium life and help conserve wild
reefs. Soft corals grow quickly in captivity and are easily divided into new individuals, and so
those grown via aquaculture are often hardier and less expensive than imported corals from
the wild.
Spicules of Dendronephyta