CHAPTER 3 Cnidaria Kingdom Animalia SubKingdom Metazoa Phylum

CHAPTER 3: Cnidaria

Kingdom: Animalia Sub-Kingdom: Metazoa Phylum: Cnidaria (Coelentrata) General Characteristics 1. They are entirely aquatic including 9000 species, some in fresh water but mostly marine. 2. They are with radial symmetry. 3. The body with two layers (Diploblastic), epidermis and gastrodermis, between them there is a noncellular jelly-like material called mesoglea. 4. An internal body cavity called gastrovascular cavity, is lined by gastrodermis. The gastrovascular cavity is with a single opening (the mouth), which also serves as an anus.

Cnidaria: digestion n n Cnidarians have an internal body cavity, the gastrovascular cavity, but no one-way gut. Food enters and waste exits through the same opening, the oral cavity. Digestion takes place extracellularly within the gastrovascular cavity.

5. Nematocysts are special stinging organelles. They occur either in epidermis or gastrodermis or in both; nematocyss abundant on tentacles, they used for defense and numbing prey. 6. Two basic types of individuals are seen: a. Polyp form (Hydroid): • Tubular body, with the mouth at end directed upward. • Around the mouth is a whorl (circular) of feeding tentacles. • Only have a small amount of mesoglea. • Sessile or sedentary. b. Medusa form (Jelly fish form): • Bell-shaped or umbrella shaped body, with the centered mouth, which is directed downward. • Small tentacles, directed downward. • Possess a large amount of mesoglea • Motile or free swimming, move by weak contractions of body

Fig. 7. 2

Figure 7. 3

Cnidocytes n n Cnidocytes contain cnidae which are stinging organelles (the most common of which is the nematocyst). The cnida is a small capsule made of chitin that contains a coiled, often barbed, filament. In many cases a toxin is injected, but in others, the cnida entangles or sticks to the prey. Nematocysts of most cnidarians are not harmful to humans, but the stings of some (e. g. Portugese Man-of-war) are painful or even fatal (certain box jellyfish).

7. The reproduction is either a sexually by budding (in polyps) or sexually by gametes (in all medusa and some polyps). 8. No excretory or respiratory system present. 9. They haven't coelomic cavity (Acoelomte) 10. Cnidarians are the simplest animals equipped with nerve cells which are arranged into a nerve net, but there is no central nervous system.

Nerve net n n n The nerve net is a diffuse nervous system. Nerve impulses are transmitted between cells by the release of neurotransmitters from vesicles, which carry the signal across the synapse (gap) between cells. Unlike “higher animals” impulses can travel in both directions along a nerve because many synapses have vesicles on both sides. In cnidarians there is no brain, but in some medusae there are multiple nerve nets. For example, in Scyphozoan jellyfish there is a fast-conducting nerve net for coordinating swimming movements and a slower net to coordinate movements of tentacles.

Life Cycles n n In cnidarian life cycles polyps and medusae play different roles. Life cycles differ among groups, but usually a zygote develops into a planula larva, which is free-swimming. This larva settles and develops into a polyp.

Life Cycles n n n The polyp may reproduce asexually and generate other polyps. Or as in the Hydrozoa (hydras) and Scyphozoa (jellyfish) polyps bud off medusae. These medusae are generated asexually, but each medusa is either male or female and produces gametes, which are shed into the water and produce zygotes beginning the life cycle again.

7. 9 Life cycle of Obelia, a marine hydroid.

Classification of Cnidarias (4 Classes): n n 1. Hydrozoa 2. Scyphozoa 3. Anthozoa 4. Cubozoa

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida 1 -Sub-order: Anthomedusae Hydra sp. 1. They are solitary polyps and found in fresh water. The medusa stage is absent. 2. The body of hydra can extend to a length of 25 to 30 mm or can contract to tiny, gelatinous mass. 3. The body consists of three parts: 1. basal disc (pedal disc) for attachment to surfaces. 2. Colum, and 3. Hypostome encircled by 6 -10 tentacles. 4. The mouth opens into gastro-vascular cavity.

Pink-hearted hydroid (Hydrozoa) Porpita (a colonial Hydrozoan) Hydra (Hydrozoa)

n n n 5. They feed on a variety of small crustaceans. 6. Testes or ovaries where present, appears as rounded projections on the surface of the body, the testis is near the hypostome while ovary near the basal disc. 7. Reproduction is asexually by budding or sexually by forming eggs and sperms.

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida Sub-order: Anthomedusae Bougainvillia sp. 1. They live in the sea. 2. They form an arborescent (tree-like) colony. 3. The hydrantus possess a single whorl of filiform tentacles. 4. Free swimming medusa has four clusters of tentacles.

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida Sub Order: Anthomedusa Tubularia sp. 1. Is solitary, forms a large, pink colonies. 2. The hydranth has one basal and distal whorl or fili form tentacles. 3. Medusa attached to polyp. 4. Free swimming hydroid-like bodies are formed by medusa.

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida Sub order: Anthomedusae Pennaria sp. 1. Forms a regularly branching colony. 2. Hydranth possesses filiform basal tentacles and knobbed tentacles on the hypostome. 3. Medusa buds lack tentacles. 4. Medusa either sessile or free

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida 2 -suborder : Leptomedusa Obelia sp. 1. Is a colonial coelen terate, that lives in the sea, it is usually attached to rocks. 2. It is dimorphic, the life history includes both the polyp (hydroid) and the jelly fish (medusa) stage. 3. They hydroid form is colonial, sedentary and live attached to weeds and rocks reproduces a sexually giving the medusoid form. 4. The medusoid is solitary, free swimming and reproduces sexually giving the hydroid form.

5. The colong includes two kinds of polyps (also called zooids) a. the nutritive polyps (hydranths) or (feeding zooids) are similar to Hydra and protected by a cup-shaped structure, the hydrotheca. The hydranth has oral cone with a ring of tentacles (about 24) in the center of which the mouth opens. b. the blastostyle is the reproductive polyp which has lost the tentacles, mouth, and capacity of feed, it enclosed in a vas-shaped structure called gonotheca, and along the sides medusa-buds are formed them break away to become free swimming medusa.

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida 2 -Sub order: Leptomedusae Sertularia sp. 1. It has opposing pairs of hydrothecae along the stem. 2. The hydrothica may be bell like and not joined to the stem by a stalk. 3. They are moniliform in shape.

Phylum: Cnidaria Class: Hydrozoa Order: Hydroida 3 -Sub order: Limnomedusae Gonionemus sp. 1. It's a hydrozoan jellyfish or medusa like, it live near the sea coast. 2. In general form it is similar to the medusa of obelia, it is bell or umbrella shaped organism, the convexsurface (aboral surface) called the exumbrella while inner concave surface (oral surface) called subumbrella, which is partly closed by a membranous called velum. 3. The tentacles (which vary in number from 16 -80) are capable of contraction, and statocysts which are organs of equilibrium found between the bases of tentacles. 4. It's dioceous, the gonads either produce egg or spermatozoa.

Gonionemus sp.

Phylum: Cnidaria Class: Hydrozoa 2/Order: Hydrocorallina Sub order: Milleporina Millepora sp. 1. The suborder milleporina contain the single genus Millepora sp. 2. It's common member of coral reef fauna. 3. It forms a massive base, epidermis secret an external calcareous skeletal instead of perisarc. 4. Arising from skeletal pits and two types of polyps, nutritive polyp (concern with feeding) known as gastrozooids, and (dactylozooids) for capturing prey. Each gastro zooids surrounded by five or six dactylozooids. 5. Medusa is simple with four of five tentacles. 6. Sometimes called the stinging coral because of its powerful nematocysts.

Phylum: Cnidaria 2/class: Scyphozoa Order: Semaeostomeae Aurelia sp. 1. Is one of the commonest of the scyphozoan jellyfishes of worldwide distribution. 2. Members of the genus may be recognized by eight shallow lobes of the umbrella margin, and the fringe of many small tentacles. 3. The eight sense organs of Aurellia sp. Lie between the marginal lappets and are known as rhopalia. They contain organs of equilibrium. 4. Mouth is on a short marnubrium hangs centrally from subumbrella surface between four tapering oral arms. 5. Oral arms are grooved and bear nematocysts. 6. The mouth leads into gastric cavity, which is extended into fourgastric pouches (these contain the gonads).

7. There are four horse shoe-shaped gonads lie in the floor of the gastric pouches. Sexes are separate. 8. An alternation of generations of occurs in Aurelia.

3/class: Anthozoa (Actinozoa) Sub-class: Zoantharia Order: Actiniaria Metridium sp. 1. Sea anemone are cylindrical in shape with a crown of tentacles arranged in one or more circles around the mouth of the flat oral disc and it has a basal disc for adhesion to substratum. 2. The tentacles as well as the body or column can be expanded and contracted. 3. The Skin is soft but rough and contains no skeletal structures. 4. The tentacles capture small organisms by means of nematocysts and carry the food thus obtained into the mouth. 5. The slit-shaped mouth leads into a pharynx at one or both ends of the mouth is a ciliated groove called siphonoglyph, which extends into the pharynx-the siphonoglyph creates a water current directed into the pharynx.

6. Is solitary marine and cosmopolitan. 7. Sea anemons are carnivorous feeding on fish or almost any live (and sometimes dead) animals of suitable size.

class: Anthozoa 1/sub class: Zoantharia 2/Order: Mardreporaria 1/ Astrangia sp. 1. Is a coral polyp inhabited the oceans. 2. Appear in colonies, attach to rocks near the share. 3. Each polyp is look like a small sea anemone (cylindrical in shape possessing o crown of tentacles ) 4. The most noticeable difference is presence of basal cup of calcium carbonate (Ca. CO 3) called the corallite (coral).

2/ Fungia sp. 1. It's solitary, large, concave below and convex above. 2. Has no siphonoglyph. 3. It has a large shape. 4. Has calcareous exoskeleton. 3/ Acropora sp. 1. Is an important genus of reef building cards. 2. Most species of Acropora are branched colonies. 4/Oculine sp. Forms a dendritic compact colony with zooids spirally arranged and widely separated.

7. 27 Soft coral (Octocorallia)

Sea fan (gorgonian)

Red gorgonian

Coral Reefs n n n Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support and protect the coral polyps. Reefs grow best in warm, shallow, clear, sunny and agitated waters.

Coral Reefs n Many other cnidarians on reefs including octocorallians, sea anemones and hydrozoan corals also have zooxanthellae and are similarly restricted in their vertical distribution.

Types of Coral Reefs n Three general types of coral reef can be recognized. n n n Fringing reefs: are the commonest type and project into the sea directly from the shore. Barrier reefs: are separated from adjacent land by a lagoon. Great Barrier Reef is the longest at >1000 miles on NE coast of Australia. Atolls: rest on summits of submerged volcanoes. Usually circular/oval with a central lagoon. Parts of the reef platform may emerge as islands.

Shumann Island, Papua New Guinea (fringing reef).

Pohnpei Atoll Micronesia

Barrier reefs

Coral Reefs n n n A reef platform (the layer of coral rock) may extend considerably below the current photic zone (reefs more than 1000 m deep are known). How is this possible? Growth of reef platforms occurred as a result of changes in sea level or subsidence of the substratum.

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Coral Reef Diversity n n The waters in which corals are found are nutrient poor. The clear, blue color of the water is a tip-off to this. Productive waters have a lot of phytoplankton. As a result, they are usually green and light is absorbed quickly.

Coral Reef Diversity n n Despite being in nutrient poor water, coral reef ecosystems are some of the most productive marine environments. This is because the populations of algae and symbiotic zooxanthellae carry out a huge amount of photosynthesis and so form the basis for an extensive food web.

Coral Reef Diversity n n Besides cnidarians large numbers of sponges, molluscs, clams, tunicates, and bryozoans live on the reef. In addition, sponges, clams, and some worms bore into exposed coral.

Coral Reef Diversity n n The huge numbers of holes and crevices offer shelter to shrimps, crabs, worms, molluscs, fish and other animals. All of these smaller animals attract large number of predators including fish, turtles, and sharks.

nudibranch Puffer fish Blenny Green Sea turtle

Coral reef, Indonesia

Schooling jack fish

Phylum Ctenophora n n n The phylum Ctenophora is a small phylum of fewer than 100 species of comb jellies all of which are marine. Comb jellies are named for the 8 rows of short, comb-like plates of long cilia they beat in order to move. Most ctenophores are free swimming. Beating of the cilia in each row begins at the aboral end all plates beat in synchrony to move the ctenophore. An organ called the apical sense organ coordinates beating of the comb rows.

7. 28 7. 30

Phylum Ctenophora n n Ctenophores are quite similar to cnidarians in many ways: but there a number of differences: Similarities: both have: n n n nerve net diploblastic with thick gelatinous mesoglea Pelagic, transparent floating predators, slow moving Single oral cavity Tentacles solid not hollow Differences: n n n Biradially symmetrical rather than radially symmetrical. Ctenophores lack nematocysts, have colloblasts Ctenophore cells are multiciliated Cnidaria swim by jet propulsion, ctenophores by beating of combs Like cnidarians ctenohores have no anus but possess anal pores, small openings to the outside from the gastrovascular cavity.

Phylum Ctenophora n n n Many ctenophores possess two long tentacles that are covered with adhesive cells called colloblasts, not nematocysts as in the cnidarians. However, one species of ctenophore does carry nematocysts, which it appears to obtain from cnidarians it eats. Unlike cnidarian tentacles, those of ctenophores can be retracted into pits or sheaths. In ctenophores without long tentacles the body is covered with colloblasts and the whole surface is used to trap prey. Small tentacles transfer prey to the mouth.

http: //www. marlin. ac. uk/images/taxonomy_descriptions/Ctenophora. jpg

Phylum Ctenophora n n n Ctenophores can be major predators of larval fish and other zooplankton such as crustaceans. The introduction of Mnemiosis leidyi an invasive species of comb jelly into the Black Sea about 25 years ago caused the collapse of the local anchovy fishery. The comb jellies consumed fish eggs and larvae as well as competed with fish for zoo plankton