Cnidaria and Ctenophora PDF

CNIDARIA  DIAGNISTIC FEATURES Radially symmetrical which allows food capturing from all sides. However, there may be modifications. They are diploblastic; the epidermis and gastrodermis are separated by jelly-like mesoglea There is a single gastrovascular cavity that opens only thr...

CNIDARIA  DIAGNISTIC FEATURES Radially symmetrical which allows food capturing from all sides. However, there may be modifications. They are diploblastic; the epidermis and gastrodermis are separated by jelly-like mesoglea There is a single gastrovascular cavity that opens only through the mouth. There is no anus.  There is no head, brain and CNS. It has a simple nervous system of interconnecting nerve cell which form nerve net. Statocysts and oceli are usually the only sense organs. The skeletal system may be horny or calcerous, internal or external or continuous. There is no special structures for respiration, excretion and transport system (except sea water channels in some large jelly fish.  Possession of a unique stinging or adhesive structure called cnidae which risides in a cell called cnidocyte. The most common cnidae are called nematocyst.  They usually exhibit polymorphism. Existing either as a solitary or colonial sessile polyp or free floating medusa.  Most polypoid hyrozoans are colonial and polymorphic eg Obelia. Obelia Pedal disc or physa stalk or Stolon in colonial form  Commonly form colonies by asexual reproduction which help them to attend forms and sizes unattainable by a single individual.  Four CLASSES are recognized: Hydrzoa, Scyphozoa, Cubozoa and Anthozoa HYDROZOA The enteron is not divided up by mesenteries The tentacles of the polyp are usually solid The mesoglea is acellular Polypoid Hydra Hydra capturing water flea Very long pendant manubrium of a hydromedusa  Cnidocytes are only found in epidermis Skeleton is external and usually chitinous Hydromedusa are small and are the gamete producing individuals The gametes are ectodermal Craspedote  Ex-umbrallar surface Sub-umbrallar surface Medusa Hydra viridis  HYDROZOA HYDROIDA – GYMNOBLASTEA Hydra, Bougainvilla, Hydractinia,Calycopsis, Turbularia – Calyptoblastea Gonionemus, Obelia, Plumularia, Lovenella TRACHYLINA Polypodium, cunina, Myxidium SIPHONOPHORA Physalia, Eudoxoides, Apolemia CHONDROPHORA Velella, Porpita ACTINULIDA Halammohydra, Otohydra  Scyphozoa Medusa is usually the dominant form. Unlike hydromedusa, scyphomedusa lack velum acraspedote The margin of medusa is fringed by short tentacles and is divided by notches  The mesoglea contains amoeboid mesenchyme cells Cnidocytes occur in the gastrodermis as well as the epidermis Gametes are gastrodermal in origin CUBOZOA(BOX JELLY)  Medusa is square shaped with a marginal self or velum and have a tentacle or group of tentacles which hang from each corners of the square. They are strong swimmers and voracious predators of fish which relates to the elaborate image forming eyes with which they can maneuver obstacles. The stings of some species (eg. Chironex) can be lethal to humans.  ANTHOZOA(SEA ANEMONES AND CORAL) Only the polyp with limited mobility predominates. The oral end is expanded into an oral disc bearing hollow tentacles surrounding the slit-like mouth The gastrovascular cavity is divided into compartments by complete or incomplete mesenteries  Mesenteries bears cnidocytes and gonads The mesoglea contains amoeboid mesenchyme cells The mouth leads into a pharynx At one or both end of the mouth is a siphonoglyph which move water into the gastrovascular cavity Reef forming Anthozoa polyps  CTENOPHORA COMB JELLY, SEA WALNUT SEA GOOSE, SEA BERRY Comb jellies are biradial symmetrical transparent, fragile, acoelomate luminescent marine animal The outer surface bear eight meridonal bands of cilia that resemble comb between the oral and aboral poles. Stotocyst coordinated beating of the cilia move the animal through water Mnemiopsis  Comb jellies are the largest animals that move by means of cilia. They have gelatinous mesenchyme from which the musculature is formed. Monomorphic and without any kind of an attached sessile life stage. Pleurobrachia  Most are hermaphroditic, typically with a characteristic cydippid larval stage They have complete gut. The gut has pharynx which leads to a branching gastrovascular canal system that ends in two small anal pores. They do not have stinging nematocyst, however, the tentacles are equipped with adhesive glue cells called colloblast.  The colloblast releases sticky thread that traps prey that comes in contact with the tentacle Ingestion occurs as the tentacles are wipe across the mouth.  SIMILARITY WITH THE CNIDARIA Radial symmetry Possession of feeding tentacle Gelatinous medusa-like form Acoelomate Presence of relatively simple nervous system consisting of nerve net.  DISTINCTION FROM CNIDARIA No stinging nematocysts Have mouth for food intake and two anal pores for egestion of water and waste at the other end. Monomorphic throughout their life history Never colonial They have wholly mesenchymal musculature (perhaps mesodermal)