1 EXERCISE 5 CNIDARLA: OBSERVATION AND I I CLASSIIi'IIICATBBN OF SPECIMENS Structure I 5.1 Introduction I 0b.jcctives 5.2 Material Required 5.3 Observation of Cnidarians I Ol~elicrColony Mcdustl of Ohelia I I'lrysolia I A l~relio Aie~rrdi~r~ii rlcroporo 'J'.S. of I(vdro through Tostis T.S. 01'1-[vdrnthrough Clvtlry 5.4 Terminal Questions -,. , -. 5.1 INTRODUCTION Tlie phylum Cnidaria or Coelenterata, includes the faliiiliar hydras, jelly fishes, sea . anemones and corals. You have olreacly studied about Cnidarialis in Units 4 and 7 of LSE-09 course. These are often brilliantly colourcd. They exhibit radial sy~nnietry, The Cnidarians possess two basic metazoall structural features. Onc, there is an intenla1 space for digestion, called in Cnidarinns as gastrovasc~~larcavity. This cavity lies along the polar axis of the animal atid opens to tlie outside at one end to for111 n ~noutli,Tlie presence of a mouth a~iddigestive cavity permits the use of a mucll greater rnlige of food sizes than is possible in tlie protozoarls and sponges. Two, in C~lidariailsa circle of tentacles, representing exte~lsiollsof the body wall, surrounds tlie ~lioiltlito aid in tlie capture and ingestion of food. Tlie Cnidarian body wall consists of three basic layers: an outer lnycr of cpidennis, nn inner layer of elidoder~nalcells lining Ilie gastrovnsci~larcavity, and between these two a layer called mesoglea. The rnesoglea ranges from n tliin, no~~-celli~larmen~branc to a thick, fibrous, jelly-like, 111~1coidlnaterial with or without wanderillg a~noebocytes,A considerable i~umberof different cell types compose tlie epidermis and gastrader~nis,but there is only a limited degree of organ developme~lt, Tlie different stri~ctilraltypes are present within tlie phyli1111,One type, wl~icllis sessile, is k~~ownas the polyp, The other farm is free swim~ningand is called the medusa. Typically, the body of a polyp is a tube or cylinder in wllich tlie oral CII~,bearing the mouth and tentacles, is directed ilpward, and the opposite, or aboral elid is attached, The 111edusoid body resembles a bell ar an i~lnbrellnwith the convex side upward and the moutll located in tlie centre of tlie collcnve undersurface, The tentacles hnng dsw~i from tlie margin of the wall. In contrast to the polypoid ~i~esoglea(middle layer) wliicll is more ar less thin, the medusoid mesoglea is extreinely thick and'constitutes tlie bulk of tlie ani~nal,Becai~se of this mass ofjelly-like ~nesoglealmaterial, these Cnidarian forms are comrno~llyk~iow~i as Jellymfish.Some Cnidarians exhibit only tlie polyp farm, same only the merdusoid form, while others pass tl~rollgl~both in their life cycle. Except for the hydras that are foi111d ill fresh water, cnidarians are marine and are found in sl~allow waters. Qbjectives This exercise will ellable yo11 to: identify the specilne~~and give its scientific atid colnrnon [lame, classify LIPto CIBSS level, and give tl~creflsolis for tlie classificstia~llistad by yau, , Animal Diversity Lab. e draw a labelled diagram of tlie specimen, and e monitor any special features in the life liistory. 5.2 MATERIAL REQUIRED I. Museum specimens - Plvsalia, Aurelia, Sea Anemone, Acropora 2. Co~npou~idlnicroscope 3. Binocular In icroscope 4. Permanent slides - Obelia colony, Medusa of Obelia, T.S. of Hydra through testis a~idovary. 5.3 OBSERVATION OF CNIDARIANS C~iidariaare Radiata in which: I. Nernatocysts are present. 2. Adult movement is by muscular activity. 3. Tlie body is either a polyp or a medusa, and these alternate in the life-cycle of Inany species. 4. A plaliula larva is developed. 5.3.1 Obelia Colony Examine the slide under low power of mic~~oscope/binocular.Note tlie details of the colo~lystarting from its basal elid to the. terminal structure. On tlie brarlclies note different types of zooids and their distinctio.ns from each otlier. General Characters Obelia colony is a highly branched structure and consists of a liorizo~italliydrorrlliza attached to tlie substratum and several vertical branches or liydrocauli wllicli bear zooids. The cololiy is dimorpllic consisti~igof: i) Polyps or hydranttis that: are nutritive zooids having vase-shaped body with mouth and tentacles. Tlie polyp is enclosed by a perisarcal covering called hydrotheca. i i) Blastosty les are c lu b-shaped without tentacles. Tliese are enclosed in gonotlieca, the perisarcal covering. Buds arise from its axis, wliicli develop into medusae. iii) Life history exhibits regular alternation of asexual and sexual ge~ieratio~ior metagenesis. Habit and Habitat Marine, colonial, sedentary, in.sliallow water region, attached to substratu~n. Geographical Distribution Widely distributed froin ~rcticregion down to Gulf of Mexico and Pacific Coasts. Classification and its Justification Kiiigdo~n Animalia Animals, multi-cellular organisms with cel Is tliat lack a cell wall, many capable of movement or movement of some of their body parts or capable of movement at some time of their life cycle; heterotrophic nutrition. Phylum Cnidaria Nematocysts are present, adult movement is by muscular activity. The body is either a polyp or a medusa, and these alternate in the life cycle of many species. A planula larva is developed. I Cnidnria: Observation 1 Class Nydrozoa Tlle polyp typically alternate wit11 tlle medusa. and Classification of Tlle medusa possesses a velum and a nerve -Specimens ring. The eilteron is not subdivided by vertical septa, The gonads are ectodermal in origin. Tllere may or may not be a skeleton. The tentacles of tlle polyp are generally solid. The inembers alillost always for111 colonies. Genus Obelia , Medusabuds I Longitudinal seckion postome Blastostyb -"----- Fig. 5.1: 0l)clin colony. 5.3.2 Medusa of Obelia Examine tl~eslide of medusa of Obelia and note tlie followiilg characters. It is a life- liistory stage of Obelia. Genera1 characters The following are the identification characters of tl~eMedusa, i) Medusae are saucer-shaped. These bear gonads and produce sperm or ova for sexual reproduction. ii) Gonads are borne 01.1radial canals. iii) Medusa is a free swimming reproductive zooid of Obelia colony developing asexually on the blastostyles. Animal Diversity Lab. iv) Margin of the umbrella with a true velum and a circlet of tentacles. Medusae are craspedote i.e, with velum. v) Four adradial tentacles carry statocysts at their base. vi) Mouth rectangular borne on matiubrium which is present in the centre of inner or sub-umbrellar surface. Fig. 5.2: Medusa of Obelin. Habit and Habitat: It is a free living and swimming stage of Obelia. s Geographic Distribution: Widely distributed from Arctic region down to Gulf of Mexico and Pacific coasts. Classification and its Justification Kingdom Animalia Animals, multi-cellular orga~~ismswith cells that lack a cell wall, many capable of movement or movement of some of their body parts or capable of mqvement at some time of their life cycle; heterotrophic nutrition. Phylutn Cnidaria Netnatocysts are present. Adult movement is by muscular activity. 'The body is either a polyp or a medusa, atid these alternate in the life cycle of tnatiy species. C A planula larva is developed. Class Hydrozoa The polyp typically alternate with the medusa. The medusa possesses a velum and a nerve ring. The enteron is not subdivided by vertical septa. The gonads are ectoderrnal in origin. There may or may not be a skeleton. The tentacles of the polyp are generally solid. The members almost always form colonies. Genus Obelin 5.3.3 Physalia Observe the specimen in the jar from all sides. You will be able to observe the following characters. General characters i) It is a colonial form, brightly coloured, blue or purple unichambered float - the pneurnatophore, filled with gas having the composition of air. Cnidarin: Observation ii) The gas is secreted by gas gla~ldpresent in the underside oftlle pneumatophore. It and Classification of is hydrostatic in filnction. a Specimens iii) Upper sr~rfaceof the float is drawn into a sail or crest and has an opellin$ called pneumatopo~-e. iv) Physalicr exhibit the highest degree of polymorphism. Tlie colony consists of: - Gastrozooids or nutritive zooids with mouth but witlioirt tentacles. - Blastostyles or gonophores or reproductive zooids bear cl~~stersof medusae, - Dactylozooids or protective zooids with tentacles and nematocysts. - Tentacles are very long and coiled. Carry batteries of nematocysts. - Collection of all of the zooids for~liscormidia. v) It is popula~-lyknown as POI-tugueseman -of-war. ("Man-of-war" refer's to a warship denoting its l~iglilyaggressive ~lat~~reas a predator) nematocysts Fig. 5,3: Physnlio. , Habit and Habitat Marine? pelagic, colonial and floating form. -'. General ~i&riQution 4. Found in tropical and si~btropicalseas. Clsrssific~tionand its Justification Kingdom Animalfa Animals, multi-cellular orga~~ismswith cells that lack a cell wall, many capable of movement or moveme~lt of some of their body parts or capable of movetnent at some time of their life cycle; lieterotrophic nutrition. Phylum Cnidriria Ne~fiatocystsare present. Adult ~nove~nentis by tnuscular activity. The body is either a polyp or a medusa, and these alternate in the life cycle of many species. A planula larva is developed. Animal Diversity Lab. Class Myd rozoa The polyp typically alternate with tlie medusa. Tlie medusa possesses a velum and a nerve ring. TIie enteron is not subdivided by vertical septa. Tlie gonads are ectodermal in origin. Tliere ]nay or may not be a skeleton. Tlie tentacles of tlie polyp are generally solid. Tlie members almost always form colonies. Genus Pizysnlia Co~n~nollname Portugese Man of War 5.3.4 Aurelin Observe tlie specimer~in tlie jar from different sides, and study the details. General Characters Aurelia is disc-shaped with a convex exu~nbrellarsurface and a concave subumbrellar surface.