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#21
Saturday, April 25, 2009
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Protozoan reproduction.
Protozoan reproduction.
Although i have given a link of rep in protozoa its not comprehensive. the link i am mentioning now has both detailed description and diagrams of asexual and sexual reproduction. Clich here regards 
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Shali (Thursday, October 08, 2009) | ||
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#22
Sunday, April 26, 2009
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Zoology Glossary
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When you have to shoot, shoot. Don't talk. ~ The Good, The Bad, and the Ugly Last edited by Viceroy; Sunday, April 26, 2009 at 10:25 AM.
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AFRMS (Sunday, April 26, 2009) | ||
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#24
Sunday, April 26, 2009
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Porifera.
All about Porifera.Its a 17 page presentation and easily downloaded.
And in the end the classification is also given. With this most of the phylum porifera is complete now. Click Here Regards
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#25
Monday, April 27, 2009
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@afrms
You mentioned in some of your post about a couple of articles published in Dawn. I tried to find that peculiar post but couldn't succeed. Would you please write again about the title and date on which they were printed? Regards,
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#26
Monday, April 27, 2009
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Quote:
I think you are talking about post 3 in the thread linked here
__________________
When you have to shoot, shoot. Don't talk. ~ The Good, The Bad, and the Ugly
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| The Following 2 Users Say Thank You to Viceroy For This Useful Post: | ||
AFRMS (Monday, April 27, 2009), Lord AvaLon (Monday, April 27, 2009) | ||
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#27
Monday, April 27, 2009
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Quote:
Mohsin has mentioned the link.i was going through the Dawn news articles and found a good article on Irrigation System. The title is "giving irrigation system a facelift" By bilal hassan.(economic and bsuiness reveiw,feb 16-22 P.III. do check it might be helpful. regards
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| The Following User Says Thank You to AFRMS For This Useful Post: | ||
Lord AvaLon (Monday, April 27, 2009) | ||
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#28
Monday, April 27, 2009
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That was helpful afrms,
I request you to keep on pointing out the articles which appears important to you in anyway. Having the clippings would obviously help alot in the high times of exam. Regards,
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#29
Monday, April 27, 2009
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Quote:
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#30
Monday, April 27, 2009
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Phylum Coelenterata
Phylum Coelenterata
The radiate animals Phylum Coelenterata ( Cnidaria ) The Phylum Coelenterata includes the polyps, jellyfishes, sea anemones, and corals. All of these animals have a body wall consisting of two layers of cells, between which is a jellylike substance, the mesoglea. Within the body is a single gastrovascular cavity, or coelenteron. Because of the presence of two cellular layers, Coelenterates are side to have a tissue-level organization. They are also acoelomates; that is, they dont possess a second body cavity, the coelom . Position in animal kingdom Phylum Cnidaria are characterized by primary radial or biradial symmetry . Radial symmetry , in which the body parts are arranged concentrically around the oral-aboral axis , is particularly suitable for sessile or sedentary animals . The phylum has not advanced generally beyond the tissue level of organization, although a few organs occur . Biologic contributions a. The phylum has developed two well-defined germ layers , ectoderm and endoderm ; a third , or mesodermal ,layer , which is derived embryologically from the ectoderm , is present in some . The body plan is saclike , and the body wall is composed of two distinct layers , epidermis and gastrodermis , derived from the ectoderm and endoderm , respectively . The gelatinous matrix , mesoglea , between these layers may be structureless , may contain a few cells and fibers , or may be composed largely of mesodermal connective tissue and muscle fibers . b. An internal body cavity, the gastrovascular cavity , is lined by the gastrodermis and has a single opening , the mouth , which also serves as the anus . c. Extracellular digestion occurs in the gastrovascular cavity , as does intracellular digestion in the gastrodermal cells . d. Most radiates have tentacles , or extensible projections around the oral end , that aid in food capture . e. The first true nerve cells ( protoneurons ) occur in the radiates , but the nerves are arranged as a nerve net , with no central nervous system . f. Sense organs appear first in the radiates and include well-developed statocysts (organs of equilibrium ) and ocelli. g. Locomotion in the free-moving forms is achieved either by muscular contractions . However the groups are still better adapted to floating or being carried by currents than to strong swimming . h. Polymorphism (polyp stage and medusa stage ) in the cnidarians has widened their ecologic possibilities . i. Some unique features are found in this phylum , such as nematocysts ( stinging organoids ) in Cnidarians . characteristics a. Entirely aquatic , some in fresh water but mostly marine b. Radial symmetry or biradial symmetry around a longitudinal axis with oral and aboral ends ; no definite head c. Two basic types of individuals: polyps and medusae d. Exoskeleton or endoskeleton of chitinous, calcareous , or protein components in some g. Special stinging cell organoids called nematocysts in either or both epidermis and gastrodermis ; nematocysts abundant on tentacles , where they may form batteries or rings h. Nerve net with symmetric and asymmetric synapses; with some sensory organs; diffuse conduction e. Body with two layers, epidermis and gastrodermis, with mesoglea ( diploblastic ) ; mesoglea with cells and connective tissue ( ectomesoderm ) in some ( triploblastic ) f. Gastrovascular cavity (often branched or divided with septa ) with a single opening that serves as both mouth and anus; extensible tentacles usually encircling the mouth or oral region i. Reproduction by asexual budding ( in polyps ) or sexual reproduction by gametes ( in all medusae and some polyps ) ; sexual forms monoecious or dioecious ; planula larva ; holoblastic cleavage . j. No excretory or respiratory systems k. No coelomic cavity Classification a. Class Hydrozoa This class includes the freshwater polyps , the small jellyfishes , the hydroid zoophytes, and a few stony corals . b. Class Scyphozoa Most of the large jellyfishes are placed in this class . c. Class Anthozoa In this class are included the sea anemones , and most of the stony and horny corals . Class Hydrozoa (1) Characteristics a. solitary or colonial ; b. asexual polyps and sexual medusae , although one type may be suppressed ; c. hydranths with no mesenteries. d. medusae ( when present ) with a velum; e. both fresh-water and marine . (2) Typical animal Hydra a. The structure of hydra ; b. The physiological function of hydra ; c. The life cycle of hydra . Class Scyphozoa (1) Characteristics of Class Scyphozoa a. solitary ; b. polyp stage reduced or absent ; c. bell-shaped medusae without velum ; d. gelatinous mesoglea much enlarged ; e. margin of bell or umbrella typically with eight notches that are provided with sense organs ; f. all marine Typical animal Aurelia aurita a. The structure of Aurelia aurita b. The life cycle of Aurelia aurita Class Anthozoa (1) characteristics a. all polyps, no medusae ; b. solitary or colonial ; c. enteron subdivided by at least 8 mesenteries or septa bearing nematocysts; d. gonads endodermal ; e. all marine . (2) Typical animal sea-anemones Metamorphosis Generally, after swimming for a few hours to many days the planula attaches and develops into a polyp or polypoid form , which in colonial species subsequently gives rise to the colony . In some hydroids the planula remains in the gonophore, developing into the tentaculate actinula larva which is liberated and creeps about . After attachment, it develops into a polyp . In many hydrozoans with no polypoid phase the planula develops into an actinula and then a medusa . In most scyphozoans, after attachment, the planula develops into a polypoid scyphistoma, with a stalked trumpet-shaped body . At maturity, the scyphistoma produces a free-swimming medusa stage, the ephyra larva, by transverse fission or strobilization. Ephyrae may be produced singly or several at a time, and develop to adult medusae . In zoantharian anthozoans, the planula does not attach but develops into an anemone-like Edwardsia larva, then the Halcampoides larva. After attachment, tentacles develop and the adult polyp form is attained. Reproduction There are both dioecious and hermaphroditic species . Sexual reproduction Asexual reproduction Asexual reproduction is common, it may occur by : a. budding ; b. pedal laceration, e.g. in sea anemones ; c. transverse fission, e.g. in the production of ephyrae by scyphistomae d. longitudinal fission , e.g. in many sea anemones . Polymorphism In many cnidarians the life-cycle contains two morphologically dissimilar individuals , the pulp and the medusa . In colonial species, each of these types may occur in a number of different morphological forms , specialized to perform a particular function . The main types of modified polyp are : a. the gastrozooid ---- feeding polyp b. the gonozooid ---- reproductive polyp c. the dactylozooid ---- protective polyp , or tentaculozooid a, b and c are found in hydrozoan colonies d. the autozooid ---- feeding and reproductive polyp e. the siphonozooid ---- current producing polyp d, and e are found in some authozoan colonies A colony may also bear medusoid forms in different stages of formation or degeneration, which may or may not be freed . Medusae may become modified as swimming bells, floats , protective bracts or phyllozooids, or gonophores which serve only for reproduction . Phylum Ctenophora About 100 species known . Ovoid forms measure up to about 5 cm , flattened forms may be up to 1 meter or more in length . (1) Characteristics a. symmetry biradial ; arrangement of internal canals and the position of the paired tentacles change the radial symmetry into a combination of the two ( radial + bilateral ) b. usually ellipsoidal or spherical in shape , with radially arranged rows of comb plates for swimming c. Ectoderm , endoderm , and a mesoglea ( ectomesoderm ) with scattered cells and muscle fibers ; may be considered tripoblastic d. Nematocysts absent ( except in one species ) , but adhesive cells ( colloblasts ) present e. Digestive system consisting of mouth, pharynx , stomach , and a serious of canals f. Nervous system consisting of a subepidermal plexus concentrated around the mouth and beneath the comb plate rows; an aboral sense organ ( statocyst ) g. No polymorphism or attached stages h. Reproduction monoecious, gonads ( endodermal origin ) on the walls of the digestive canals , which are under the rows of comb plates ; determinate cleavage ; cydippid larva i. Luminescence common Comparison with Cnidaria A. Ctenophores resemble the cnidarians in the following ways: a. Form of radial symmetry ; together with the cnidarians , they form the group Radiata b. Aboral - oral axis around which the parts are arranged c. Well - developed gelatinous ectomesoderm d. No coelomic cavity e. Diffuse nerve plexus f. Lack of organ systems B. They differ from the cnidarians in the following ways: a. No nematocysts except in Euchlora b. Development of muscle cells from mesenchyme c. Presence of comb plates and colloblasts d. Mosaic, or determinate type of development e. Presence of pharynx generally f. No polymorphism Classification Class Tentaculata With tentacles. Tentacles may or may not have sheaths into which they retract . Some types flattened for creeping ; other compressed to a bandlike form . In some the comb plates may be confined to the larval form. Class Nuda Without tentacles; conical form; wide mouth and pharynx; gastrovascular canals much branched .  
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dr.atifrana (Thursday, April 30, 2009), Shali (Thursday, October 08, 2009) | ||
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