Unit 2: Cnidaria and Ctenophora

Unit-2 classmate Dele 30 Cnidaria & Ctenophora General Characteristics and classification of Cnidaria upto clases SN Definition The Coelenterata (en) Cnidaria may be defined as diploblastic metazoa with tissue grade of organisation having nematocysts and a single gastrovascular cavity". General characters All ane aquatics, Some fresh water and some marine. They are free-living Organisms. Metazoans with tissue grade of organisation.. Body may be Symmetrical, radial (ann) bircadial symmetrical. Exo-skeleton is chitinous Le made up of calcium Carbonate. Herce Known as Chitinous (an) Calcannious exoskeleton. Acoelomate animals (Coelom Body cavity & acoelomate absence of body Cavity) 1 T They are Uscially Carnivores Respiratory System, cinculatory System & excretory system are not well developed ie they are wanting. Reproduction is by both sexual & asexual methods. Development is indirect type including larval stage. *Direct type doesnot include larval stage.. Classification phyllum Coelentercata includes 111000 known species, half of which are extinct Phylum Coelenterata is divided into 3 classes. Class-1 (Hydrozoa): Freshwater Organisms, but some are marine They are firee-living. Exhibit radial Symmetry body. Medusae is present with vellum They are minoecaeus & dioeceous Sexcells are directly discharged to Outside, Ex÷ hydra, Obelia, Plumularia, Campantulania te 2 Class-2 (Scyphozoa) Includes lange jelly fishes They are exclusively menine organisms. Respimatony excretory system are not well developed. True medusoid form is absent sexcells are well developed. EX periphyla, Aunelia etc. Class-3 (Anthozoa) They are exclusively manine. All are polyps, nameduseid forums. are present Body exhibit birradial Symmetry Gastrovasculan Cavity is divided into 8 (on) mone compartments Exoskeleton is formed by Cacas de calcium Carbonate campound. Fertillization is external type.. Ex: Tubipora Hellopona etc. Metagenesis in Obelia In Obelia life cycle includes two clearly defined phases. fixed Polypeid phase (hydroid colony) and. Pelagi meclusoid phase. Hydroid colony has no yonads and reproduces by asexual budding to give nise to medusae alternation of generiations, a phenomenon in which a diploid asexual On the other hand medusas reproduce exclusively by sexual method to give rise to new hydroid colonies. This fact apparently seems to have given rise to the idea of phase and a haploid sexual phase regularly alternates with each other in the life history of an organism. But, in obelia medusaid phase doesnot represent Sexual generation because a true thapkid Medusa arises from blastastyle (diploid) by a process of asexual budding. It means medusa too is a diploid zeoid Sex cells danat Originate in Medusa, but in the epidermis of blastostyle, from where they migrate into gonads of medusa. These facts show that medusa dou's not represent a sexual genercation. It is simply a free swimming dipalid zooid specialised for dispersal of gametes of the sedentary tydroid colony Infact the so called sexual generation in Obelia is indistined & represented by haploid gametes only. Thus in abelia asexual hydroid colony & sexual medusa merely represent different phases on zavids, an example of polymerhism.. and belong to a single diploid generation. So, that a true alternation of generiation cannot be said to Occur in Obelia rather it is termed metagenesis lay some conkeres CORALS Corals arce marine, mostly Colonial and polypoid Coelenterates living in a skeleton of Calcium Carbonate Secreted by themselves. Some of them grow into massive structures while others forem lange branched Colonies. Most of the Corcals belongs to the class anthozoa and a few to Class hydrozea. STRUCTURE OF CORAL POLYP A typical Corral polyp is a small organism about 10mm long and 1-2mm in diameter. A basal dise is absent as its basal region is around by Calcareous exoskeleton. Mesenteries are restricted to the upper part of Coelentercon. Muscles are poorly developed. CORAL SKELETON Skeleton of Conal is known as Coralite It is Calcarious exoskeleton Secreted by epidermis. Each Conalite is like a Stony cup with a basal plate and a Sup wall is known as theca enclosing the abonal portion of the polyp.. Inner ends. are fused to forum an Known as Columella. regular Central skeleton which is In a calanial Cornal corialites of individual polyp fuse together to form a skeletal mass called Corallum TYPES OF CORALS IN DIFFERENT GROUP Hydrozoans Corals: The hydrozoan Corrals belong to Onden Milleparina Ex include Millepona It also includes another onder Styl asteriia and the example includes Sty lasten Within the exoskeletons two types of polypoid forms are found that ane gastrozooid and dactylozooid. Anthazoan Corrals: The anthozoan Cormal's belongs to the sub-class-Octa-Corallia and hexa.comallia. Subclass Octacomallia belongs to Creden - stoloniferca (Tubipora), Onden-Alcyonacea (Alcyonium), Orden - Coenothecalia (Heliopana) and Onden-Gorgonacia (gongonea). The sub-class hexacorallia belongs to Orden Madreportaria (Astraea, Madreporca) & Order - Antipathania (Antipathes) - Onden Stalonpherra include Ongan pipe Coral which is widely distributed in warm waters. These skeletons arce dull red in colour due to the presence of iron salli Ondere Coenothecalia includes single genus Helioporra which is known as Blue Coral Gorgonacea includes plant like colonies of sea fans Corralsalso known as horny coral's. Order-Auntipatharcia includes black corcals like Antipathes. It is also tree like structure... Onden-Madrepararia includes story Corals ore also known. Corrals as True These arce looks like the stone (Astroea) & also Known as Mushroom Corcals. Another example of madre pomarcia is fungiea which is known as Brain Corral. The corals have diverse in sex and sizes. Some are colonial with small polyps and same ane large branched Structures. Corcal Colonies are most abudant in tropical areas They are found mostly at a temperaturce above 22°c. Coral Reefs What are Coral reefs ? Coral colonies grow in size by budding of polyps Continuosly and of ten forum extensive masses, Known as coral reefs. According to Vaughan (1917), a Corcal reet is a ridge in mound of limestone, the Upper Surface of which is near the surface of the sea and which is formed chiefly of Caca secreted by Coral polyps. →The Corral meets are produced by Corcals belonging to Anthozoa, Particularly. Hence, these are supposed to be the principle builders of Coral reefs through there are other contributors also. Distribution Coral reefs are limited to the Indo-Pacific, the Centrial western pacific, and the Canibbean regions of north of Bermuda. Bermuda is a Conal island where houses are built of Corral blocks Around India, coral reets are found off part Okha and Dwarka in the gulf of kutch and also gulf of mannen between India and Srilanka Corral reefs are also located at Andaman and Nicobar island and at Lakshadweep islands Conditions of Reef formation: The coral reefs grow. best at a depth of about normally in warm waters upto about 20°c... 30 metres on less and. Light and amount of sediment also limit the reef forening Cocals... They also fail to grow in dark shaded areas and They Completely die In total darkness. Below 50 meines no reeef building Corrals are found... Components of Conal neefs In addition to stony corals, Other Components in the formation of Conal neets are millepona, Tubipana, Helioporia, Aleyon aria, Gongonians Foraminifera, wralline algae and branching algae etc. The coral reets ane also inhabited by a no of Startishes, Crabs, snails, bivalves etc. Sponges, à Sea- Types of coral reefs Conal reets are classified into & major types Keinging, Beets Coral reels lying close to the shores of some valcariic island termed fringing neefs on shore reefs. ane These are built from the sea bottom and extend from the shone upto quarter mile with the most active zone of the corral gorous facing the sea. This seaward zone is called edge on front However, sometimes reef beds are Channels called Lagoon.. broken to nesalt into irenegulan Such reefs are Composed of Corral sand, mud. Conal colonies and other animals... dead are living fringing reefs is very common in East Indies. 2 Barrier Reef The barrier reefs in the sea nearly are like Fringing reefs but they Ikim to 15 km away from the shorce. are Situated The Stretch of water, separating the barrier reef from land called Lagoon + may be half a mile to 10 miles ac morre in width. (feet) The Lagoon may-be 10-50 fathom's deep and hence suitable fore navigation. The Great Barrier Reef on the north-east Coast of Austraalia is about 2,000km long and up to 150km from share. Atoll Reef The atoll reeef, also referred to as Coral island on lagoon island is a Circulare on horse-shoe shaped meet enclosing a lagoon but not an island. The Lagoon varies from a few to about dokim across It ma may be complete are broken by feur are navigable (move) a no. of channels of which only a T The atoll of Bikine, lies in the pacific Ocean, famous for atomic hydrogen bomb tests. Formation of Corral reefs ↳ Many theorcies have been advanced to explain the Corral reef formation, but none are Two theories Seem to be entirely satis factory. of convincing Importance Darwin's Subsidence Theory: This theory states that corral reefs were first formed as fringing reefs on sloping shortes, they became barrriese reefs when the shorre Sank with water channel between them and the land. If the land is an island which sinks completely has caused the thickness of the reefs. then and subsidence 27 Daly's glacial-Control Theory: This theory states that during the east glacial period the formation of ice capsi lowers the Ocean Level by 160-70 metres below the present surface waves Cut the shorces to make feat platforms Suitable for growth of Corcals. As the ice Caps melts, Cortal's began to grow on the platforms and grows upwards with rising Ocean Level. 4 14 Observations of living corals shows that theirn rate of growth is from 5mm to 20cm per year. Most of the existing reefs could have formed within a period of 15,000 to 30,000 years. Economic Importance: 4 Corral reefs are much importance to oil industries because they are the favourable sites fore the accumulation of petroleum. deposits. Coral reefs serve as habitats for many plants and animals.. Some Corcals are highly priced fore their decorative value. 4 The red corral and organ pipe Coral are used in some indigenous syster of medicine in South India Corcal skeletons Serve as raw material force the preparcation of lime and Cement. Corral Skeletons are also helpful in making ridges that may act as natural barniens against sea erosion and Cyclonic storems.. Coral reefs serve as good nursery grounds for Commencially important fishes.