PHYLUM COELENTERATA

HISTORY

Phylum Coelenterates are full of natural beauties. They are all aquatic but chiefly marine, attached or pelagic. Originating from lower Cambrian, they are still flourishing and comprise about 10,000 species. Coelenterates are the first animals to have tissues. They may be solitary as Hydra or colonial like corals. Further, they may be either polypoid, medusoid existing in polyp form or medusa form or both. The phylum includes the hydroids and hydromedusae, jelly fishes, sea anemones and corals. Several hydroids may grow plant like colonies while jelly fishes and many hydroids swim freely. The flower like sea anemones stick on rocky ocean coasts and the corals with their tiny skeletons constitute reefs. Many Coelenterates are bioluminiscent. The corals are used for jewellery and other decorative purposes.

DIAGNOSTIC CHARACTERS​ OF PHYLUM COELENTERATA

  • Tissues grade animals. 
  • Diploblastic made of ectoderm, endoderm and intervening mesoglea. 
  • Only a single cavity, gastrovascular cavity or coelenteron present. 
  • Division of labour occurs.
  • Solitary or colonial, fresh-water or marine. 
  • Colony dimorphic consisting of feeding zooids or polyps and reproductive zooids or medusae, with several variations. Nematocysts present.
  • Reproduction sexual or asexual.

CLASSIFICATION OF PHYLUM COELENTERATA

PHYLUM COELENTERATA

CLASS I HYDROZOA

  • Either polypoid or medusoid or both.
  • Solitary or colonial

Order 1 Hydroidea

    1. Polypoid stage predominant.
    2.  Medusa present or absent.

Sub-order I Athecata or Anthomedusae

  1. Polyp athecate (perisarc does not form hydrotheca)
  2. Freshwater or marine
    Example :- Hydra. Ceratella, Hydractinia, Eudendrium,
    Pennaria, Bougainvillea, Tubularea.

Sub-order II Thecata or Leptomedusae

  1. Both polyp and medusae thecate (with hydrotheca and gonotheca).
  2. Statocyst mostly present.
    Example. Obelia, Plumularia. Companularia,
    Antennularia

Order 2 Hydrocorallina

    1. Exoskeleton calcareous.
    2. Polyps are gastrozooids and dactylozooids.

Sub-order I Milleporina

    1. Polyps scattered.
    2. Separate pores for gastrozooids and dactylozooids.
      Example :- Millepora

Sub-order II Stylasterina

  1. Calcareous exoskeleton, branching or encrusting.
  2. Dactylozooids surround gastrozooids.
    Example :- Stylaster.

Order 3 Trachylina

    1. Medusoid stage dominant polyps absent or poorly developed.
    2. Sense organs statocysts or tentaculocysts.

Sub-order I Trachymedusae

  1. Marginal tentacles oral.
  2. Gonads on radial canals.
    Example :- Gonionemus.

Sub-order II Narcomedusae

  1. Gonads on stomach floor.
  2. Tentaculocysts naked.
    Example :- Cunia, Aggina.

Order 4 Siphonophora

    1.  The animals show polymorphism.
    2. Different polypoid and medusoidzooids.

Sub-order I Calycophora

  1. Pneumatophore absent.
  2. Polypoid and medusoid.
    Example :- Praya, Abyla, Diphyes.

Sub-order II Physophorida

  1. Pneumatophore present.
  2. Polypoid and medusoid.
    Ex. Physalia, Porpita, Velella.
CERATELLA
CERATELLA
HYDRACTINIA
HYDRACTINIA

CLASS II SCYPHOZOA

  • Exclusively medusoid.
  • Medusae umbrella-shaped without velum.

Order 1 Stauromedusae

    1. Bell trumpet shaped.
    2. Sessile, attached by stalk.
      Example :- Lucernaria, Haliclystus.

Order 2 Cubomedusae

    1.  Bell cubical.
    2. Found in tropical and subtropical oceans.
      Example :- Charybdea, Chiropsalmus.

Order 3 Coronatae

    1. Bell conical with transverse construction.
    2. Deep see forms.
      Example :- Pericolpa.

Order 4 Semaeostomae

    1. Bell disc-shaped.
    2. Cosmopolitan.
      Example :- Aurelia, Cyanea, Pelagia, Chrysaora.

Order Semaeostomae

    1. Bell margin with no tentacle.
    2. Tropical and subtropical
      Example :- Rhizostoma, Cassiopea, Mastigias.
AURELIA​ (JELLY FISH)
AURELIA​ (JELLY FISH)
CHARYBDEA
CHARYBDEA (BOX JELLYFISH)

CLASS III ACTINOZOA (= ANTHOZOA)

  • Exclusively polypoid. No medusae.
  •  Gastrovascular cavity divided by 8 or more mesenteries.

Sub-class A :- Octocorallia

  • Tentacles and mesenteries 8 or multiple of 8.

Order 1 Stolonifera

    1. Organ pipe coral.
    2.  Polyps not fused and arise from a creeping mat or stolon.
    3. Skeleton of calcareous tubes or spicules or absent.
      Example :- Tubipora.

Order 2 Telestacea

    1. Lateral polyps on single or branched stem.
    2. Skeleton of calcareous spicules.
      Example :- Telesto.

Order 3 Alcyonacea

    1. Polyps and spicules embedded in fleshy coenenchyme
    2. Soft corals.
      Example :- Alcyonium.

Order 4 Coenothecalia

    1. Brown polyps. Skeleton massive and calcareous.
    2. Blue corals.
      Example :- Heliopora

Order 5 Gorgonacea

    1. Tree or feather like colony containing short polyps and central skeleton of Gorgonin.
      Example :- Gorgonia, Corallium.

Order 6 Pennatulacea

    1. Colony consists of stalk and rachis with lateral branches. bearing dimorphic polyps.
    2. Sea pens.
      Example :- Pennatula, Pteroides, Renilla.

Sub-class B :- Hexacorallia

  • Tentacles and mesenteries 6 or multiple of 6.

Order 1 Actiniaria

    1. Body muscular without skeleton.
    2. Tentacles and mesenteries.
      Example :- Metridium, Adamsia, Minyas, Tealia, Edwardsia,
      Actinia.

Order 2 Zoanthidia

    1.  Mostly epizoic, solitary or colonial.
    2. One complete and one incomplete mesentery in each pair.
      Example :- Zoanthus, Epizoanthus.

Order 3 Ceriantharia

    1.  Without pedal disc.
    2. Numerous mesenteries.
      Example :- Cerianthus.

Order 4 Madreporaria

    1. Solitary or Colonials hard corals.
    2. Hard calcareous skeleton.
      Example :- Madrepora, Astrea, Favia Fungia, Menadrina,
      Astrangia, Dendrophylla.
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