Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 11 PHYLUM: CNIDARIA (COELENTERATA) Cnida = nettle (stinging) Living Shores: Figure 180 A Detail of the body wall of a cnidarian Living Shores: Figure 180 B CHARACTERISTICS Multicellular animals. Body is essentially a sac with two cell layers in the body wall and a single opening, the mouth. The mouth is surrounded by tentacles, which contain stinging cells (nematocysts) that assist in capturing the prey. They are built on a circular body plan and are radially symmetrical. There are two common forms: (also see next section figure 180 A) o the polyp which attaches itself to the rock for example the sea anemone and o the medusa which is bell shaped and floats mouth downwards in the water for example the jellyfish.
CHARACTERISTICS Multicellular animals. Body is essentially a sac with two cell layers in the body wall and a single opening, the
mouth. The mouth is surrounded by tentacles, which contain stinging cells (nematocysts)
that assist in capturing the prey. They are built on a circular body plan and are radially symmetrical. There are two common forms: (also see next section figure 180 A)
o the polyp which attaches itself to the rock for example the sea anemone and o the medusa which is bell shaped and floats mouth downwards in the water
Jellyfish or jellies Sea anemones, zoanthids, sea fans, soft coral, hard coral
ORDER HYDROIDA SIPHONOPHORA
Hydroids Bluebottles
Polyps solitary or bud to form colonies
Floating colonies of several polyp-like or jelly-like individuals that are attached to a stem or disc.
Umbrella shaped jellies These animals have a barrel shaped body with a mouth at one end. The mouth is surrounded by a set of tentacles used for catching food. Medusoid stage completely lacking.
Clownfish living amongst the tentacles of a sea anemone
CLASS: ANTHOZOA
ANEMONES
Habitat Some anemones, such as the plum anemones live in small holes and cracks in intertidal zone in rock pools. Others live in caves and on reefs below the low tide. Sandy anemones crowd into sandy gullies.
Description Anemones are simple solitary polyps. They look like brightly coloured flowers and show a great variety of sizes and colours. Their bodies’ look like thin sacs filled with water – like water balloons. Its mouth is surrounded by tentacles and a curtain- like pharynx that hangs down inside the body and acts like a valve. This allows food to enter without water loss. When exposed to air they withdraw their tentacles, preventing them from drying out or being damaged.
Feeding They feed on small animals such as shrimps and fish, which they catch with the aid of the stinging cells in their tentacles. Many stinging cells (nematocysts) contain venomous liquid that subdues the prey. Some types of stinging cells are barbed and sticky, some actually wrap around the prey.
Predators They are eaten by some fish e.g. Butterfly fish and by some nudibranchs.
Did you know? Nemo and his dad Marlin – two clownfish- are exceptions to this, they live symbiotically with the giant anemone. The clownfish – also known as anemone fish - shelter amongst the tentacles of the sea anemone and are protected from the stings by a special coating of slime.
Habitat Soft coral is abundant in sub-tidal zones with a wide depth range off both the west and East Coast.
Description They form colonies of polyps with eight feathery tentacles and are sometimes brilliantly coloured to warn of their stinging capabilities. No solid limestone skeleton.
Feeding They catch zooplankton (small microscopic animals) with the stinging cells in their tentacles.
Predators
Soft corals cannot be very nutritious because much of their bulk is made up of watery mesoglea (jelly) and their energy content is among the lowest of all animals.
SEA FANS (Gorgonians)
Habitat Sea fans occur in deeper water growing in caves, on rocky reefs and in crevices where they are protected from the force of waves. They are common around the Cape Peninsula and along the south Coast.
Description The branched tree-like, colony has a stiff central rod made up of a flexible material known as gorgonia. They are usually coloured white, pink, orange or red. Tiny cup-like polyps are visible on the branches when they are feeding.
Feeding The tentacles catch minute food particles drifting in the water.
Habitat Hard or stony corals grow best in clear, warm waters and their occurrence is limited to the depth to which light can penetrate the water for the algae that are found associated with the hard coral. Coral growth is seldom found deeper than 60 metres.
Description The polyps of corals produce a limestone skeleton, secreted by the outer layer of the body wall. A few hard corals occur around the Cape for example Noble and Cup coral. Hard corals function as the main builders of coral reefs. As hard corals lay down more of their underlying limestone or calcium carbonate skeleton the reef grows. They are also important in providing both food and shelter to a large number of reef organisms.
Feeding Colonial corals cannot always obtain enough food from the water and in order to survive they have great numbers of microscopic algae (zooxanthellae) in their body walls. The algae use sunlight to make food for themselves and their hosts by means of photosynthesis. Through digestion, coral polyps release these nutrients to the algae. Coral and algae then apparently cycle these nutrients between them, reducing nutrient loss to the water. The coral also protects the algae. This relationship is called mutualism as both these organisms benefit from this arrangement. CO2 + H2O Food (Carbohydrates) + O2 + H2O
Predators Some species of fish such as parrotfish and butterfly fish, as well as some sea snails and sea slugs, feed on corals.
Coral bleaching Coral reefs have recently been affected by bleaching i.e. the discoloration or loss of its symbiotic algae. The cause of these widespread bleaching incidents is uncertain but recent research indicates that the cause may be unusually warm waters. The optimum temperature for coral growth is between 26°C and 27°C. Temperatures above 29°C cause the stressed coral polyps to actively expel the algae giving the coral a bleached appearance. Bleached corals have difficulty recovering; a reef can take years to recover, and subsequent bleaching incidents may make it impossible. Without their symbiotic algae, corals are unable to deposit the calcium carbonate skeleton that makes up the foundation of a coral reef. Not only corals, but also all reef organisms could potentially lose their habitat because of bleaching incidents, as the calcium carbonate structure of the reef erodes away.
Did you know? The activity of the zooxanthellae also assists in the release of lime for the
construction of a coral skeleton. The biggest threat to corals, apart from humans who collect them and pollute the
Habitat Ocean drifters found mainly in the open ocean, but often wash ashore.
Description Jellies have rounded bell-shaped bodies (medusae), which contain a layer of jelly that consists of approximately 95% water. This layer varies in thickness in different jellies. They have tentacles at the open end of the bell that is armed with stinging cells. There is a square mouth with oral arms called the manubrium.
Feeding They feed on small fish, shrimps and plankton e.g. fish larvae.
Predators They have very few predators of their stinging tentacles. However, they are an important source of food for some species of turtle and the ocean sunfish. Plastic bags drifting in the ocean are often mistaken for jellyfish by these animals resulting in them eating it by mistake.
Did you know? Some species are considered a delicacy in Japan. That the box jellyfish can give a painful sting and
that it’s Australian relative can kill a human being in 3 minutes.
Habitat Many of the tufts growing on rocks are hydroids and not seaweeds at all. Some hydroids are found growing on shells of snails. The hydroids protect the snail by deterring predators while the hydroids eat the scraps or waste products from the snail. This relationship is commensalism as the one organism benefits while the other organism is not harmed.
Description Hydroids form colonies, which often look like delicate trees or feathers. Other species of hydroids are branched in an orderly and elegant fashion. The tiny polyps are borne on the branches and may be housed in small cups. The polyps can extend for feeding and can retract into the cups after feeding. Some hydroids have an external sheath or perisarc made of chitin and protein. Divers avoid hydroids as they have a fairly powerful sting.
Feeding Hydroids are carnivorous and use their tentacles to catch minute shrimps, crabs, fish and eggs floating in the water. The digestive enzymes of hydroids are able to handle large prey.
Predators Predators are nudibranchs (sea slugs), flat worms and butterfly fish.
Polyps 2mm to hydroid colonies of 25cm
Did you know? Hydroids are named after Hydra, the multi-headed goddess of Greek mythology because they multiply by budding. The Goddess grew two heads in place of every one Hercules cut off.
Habitat Bluebottles live on the surface of the open ocean, but are often blown ashore by onshore winds.
Description They are unusual hydroid colonies, which consist of highly specialised individuals that are all interdependent.
Feeding They prey on small fishes that they catch with their tentacles.
Predators Marine turtles and sea swallows prey on bluebottles. Plough snails and sea slugs (nudibranchs) may eat bluebottles washed ashore.
Did you know? The painful stings of a bluebottle should be washed off with salt water and are best treated with sap from the leaf of a sour fig plant or vinegar. A medical practitioner using antihistamines should treat severe cases.
The smaller raft hydroid with a circular raft and the by-the-wind sailor with an oval raft and vertical sail are smaller colonies similar to the bluebottle. They set sail to the wind as a colony, producing a thin bright blue membrane of stiff material, orientated diagonally across the colony’s body.
Structure of the bluebottle or Portuguese man-o’-war
Identify the animals shown in the table below by giving the Phylum and the common name.
Phylum: ________________________ Common name:
Phylum: ______________________ Common name:
2. List three characteristics that all Cnidarians have in common.
3. Label the following parts on the animal below.
4. Name one interesting thing you would share with a visitor at the touch pool ________________________________________________________________________________
