Characters Classification and Economic importance of Coelenterate.

1. +General Characters of Coelenterata:

The generl character of Coelenterate is discussed as below.

• All aquatic, some freshwater, mostly marine.
• Solitary or colonial. Sedentary or free- swimming.
• Symmetry radial or biradial about a longitudinal oral-aboral axis.
• Body organization of cell tissue grade. Cells mostly scattered and specialized for different functions. Some cells form tissues like nerve net or nervous tissue.
• Exoskeleton chitinous (perisarc) or calcareous (corals).
• Body wall diploblastic with two cellular layers -outer epidermis and inner gastrodermis- with a gelatinous acellular mesoglea in between. In advanced types mesogloea with cells and connective tissue, hence triploblastic.
• Two types of individuals occur attached polyps and free-swimming medusa.Some species are notable polymorphism or variety of forms.
• The mouth of polyps and bell margin of medusae often encircled by short and slender tentacles.
• Coelom and respiratory, circulatory and excretory system wanting.
• The muscular system includes longitudinal and circular fibers formed by epitheliomuscular and endothelial-muscle cells.
• A single internal cavity, lined with gastrodermis, called gastrovascular cavity or coelenteron, into which mouth opens. The anus is absent.
• Digestion intercellular as well as extracellular.
• One or both body layers as well as peculiar stinging cell organelles or nematocysts, which serve for adhesives, food capture and offence and defense.
• Nervous system primitive, consisting of a diffuse nerve net. Central nervous system absent.
• Sensory organs form ocelli and statocysts.
• Asexual reproduction by budding or fission.Sexual reproduction by ova and sperms. Sexual forms monoecious or dioecious.
• Development includes a free swimming ciliated planula larva.
• Life history illustrates a regular alternation between the asexual polypoid stage and a sexual medusoid stage.True alternation of generations absent.

Classification:

Phylum Coelenterata includes nearly 11,000 known species half of which are extinct. These are grouped into three classes as follows:

Class 1. Hydrozoa

(Gr., hydra, water+Zoon, animal)

1. Freshwater or marine. Solitary or colonial.
2. Only polyps or both asexual polyps and sexual medusa present.
3. Polyps without stomodaeum and septa (mesentery)
4. Medusae with true velum (craspedote).
5. Mesogloea noncellular.
6. Gonads epidermal.Sexes cells directly on the outside.

Order 1. Hydroida:

1. Solitary or colonial
2. Polyploid stage predominant.
3. Medusae short-lived or absent.
4. Sense organ of medusae exclusively ectodermal.

SuborderI. Anthomedusae (Gymnoblastea)

1. Polyps and blastostyles athecate, I,e,perisarc not forming hydrothecae and gonothecae.
2. Medusa with gonads on manubrium.
3. Statocysts absent. Ocelli present in medusa.

Example: Hydra, Ceratella, Tubularia, Hydractinia, Bougainvillea, Pennaria, Eudendrium, Hydractinia, Podocoryne,etc.

Suborder II. Leptomedusae (Calyptoblastea)

1. Polyps and blastostyles thecate i,e with hydrothecae and gonothecae, respectively.
2. Medusa with gonads on radial canals.
3. Both statocysts and ocelli present in medusa.

Example: Obelia, Sertularia, Campanularia, Plumularia, Aglaophenia.

Order 2. Trachylina

1. Medusoid stage large, dominant, free-swimming and may develop directly from fertilized egg.
2. Polypoid stage reduced or absent.
3. Marginal sense organs or statocysts with endodermal statoliths.

Suborder I. Trachymedusae

1. Tentacles inserted above bell margin.
2. Gonads develop on radial canals.

Example: Gonionemus, Craspedacusta.

Suborder Ii. Narcomedusae

1. Tentacles arise between bell margin and the vertex of exumbrella.
2. Gonads present on manubrium or on the starch floor.

Example: Cunina, Cunarcha, Polycolpa.

Order 3.Hydrocorallina:

1. Fixed, colonial polypoid. Hydrozoa in which coenosarc secretes a massive exoskeleton of calcium carbonate.
2. Polyps dimorphic with slender dactylozooids and short plump gastro zooids.

Suborder 1. Milleporina

1. Dactylozooids hollow, with capitate tentacles.
2. Medusae free and devoid of mouth, digestive canals, and tentacles.

Example: Millepore.

Suborder 2. Stylasterina

1. Dactylozooids solid, without tentacles.
2. Gonophores reduced to spore sacs. Medusae not free.

Example:Stylaster.

Order 4. Siphonophora

1. Pelagic colonial hydrozoan showing extreme polymerism of zooids.
2. Polyps without oral tentacles.
3. Medusae incomplete and rarely freed.

Suborder I. Catycophora

1. Pneumatophore absent.
2. The upper end of the colony has one or more swimming bells (nectophores).

Example: Diphyes, Praya, Abyla.

Suborder II. Physophorida

The upper end of colony forms a large gas-filled float (pneumatophore).

Example : Physalia, Halistemma, Stephalia.

Order 5. Chondrophora

1. Pelagic, polymorphic polypoid colony.
2. Upper-end forms a chitinous gas-filled, oval float (pneumatophore).
3. Gonozooids produce free medusae.

Example: Porpita,Velella.

Class 2. Scyphozoa:

1. Exclusively marine and solitary forms.
2. .Medusa stage dominant. Polyp stage reduced or absent.
3. Gastrovascular cavity with gastric pouches and endodermal gastric filaments.No stomodaeum.
4. Medusa acraspedote, without distinct velum.
5. Mesogloea extensive, gelatinous,ith fibers and cells.
6. Gonads gastro dermal.Sex cells released in the digestive cavity.

Order 1. Stauromedusae(Leucernariida)

1. Bell goblet or trumpet-shaped.
2. Sessile, attached by an aboral stalk.
3. No marginal sense organs or tentaculocysts.

Example: Leucernaria, Haliclystus.

Order 2. Cubomedusae: (Carybdeida)

1. Bell cubical, ith 4 flattened sides.
2. Four perradial tentaculocysts present.

Example: charybdea, Chiropsalmus.

Order 3. Coronate

1. Bell conical, divides by a deep circular coronary groove.
2. Tentacles long, borne on pedalia.
3. Four to sixteen tentaculocysts present.

Example: Periphylla, Pericolpa.

Order 4. Discomedusae (Semaeostomae)

1. Flat saucer or disc -like umbrella.
2. Eight tentaculocysts present.
3. Square shaped mouth extending into 4 long oral arms.

Example: Aurelia, Pelagin, Cyanea, Chryasora.

Order 5. Rhizostomae

1. Bell usually hemispherical, without marginal tentacles.
2. Typically 8 or more tentaculocysts.
3. No central mouth. Oral arms fused with several small mouths.

Example: Rhizostoma, Cassiopeia, Stomolophus.

Class 3. Anthozoa (Actinozoa)

(Gr., anthos, flower+Zoios, animal)

1. Exclusively marine. Solitary or colonial.
2. All polyps, no medusae.
3. The mouth leads into a tubular stomodaeum.
4. Gastrovascular cavity subdivided by 8 or more septa or mesenteries.
5. Mesogloea stout and cellular.
6. Mesenteries with nematocysts and gastro dermal gonads.

Subclass I. Octacorallia (Alcyonaria)

1. Exclusively colonial.
2. Polyps with 8 pinnate tentacles and 8 septa.
3. Gullet with one ventral siphonoglyph.

Order 1. Stolonifera

1. Polyps arising independently from a creeping mat or stolon.
2. The skeleton of calcareous tubes or separate calcareous spicules or absent.

Example: Tubipora,Clavularia.

Order 2.Telastacea

1. Lateral polyps on simple or branched stem arising from a creeping base.
2. The skeleton of calcareous spicules.

Example:Telesto

Order 3. Alcyonacea:

1. Polyps proximally embedded in a fleshy mass or coenenchyme.
2. The skeleton of separate calcareous spicules.

Example: Soft corals,Alcyonium.

Order 4. Coenothecalia

1. Polyps embedded and connected by solenial tubes.
2. Skeleton massive, calcareous and blue-green from iron salts.

Example: Heliopora.

Order 5. Gorgonacea

1. Colony usually of plant-like branching from bearing short polyps.
2. Axial skeleton composed of horn-like gorgonin, separate or fused calcareous spicules, or both.

Example: Gorgonia and Corallium.

Order 6. Pennatulacea

1. Colony elongated, sessile. Lower part embedded in mud. The upper part consists of a very long axial polyp ith lateral branches bearing dimorphic polyps.
2. Axial skeleton of separate calcareous spicules or Horney substance.

Example: Pennatula, and Pteroeides, (Sea Pens), Renilla (sea Pansy).

Subclass II. Hexacorallia (Zoantharia)

1. Solitary or cononial.
2. Tentacles usually unbranched, numerous but never 8.
3. Gullet commonly ith 2 siphonoglyphs.

Order 1. Zoanthidea

1. Small or colonial. No skeleton.Mostly epizoic.
2. Polyps small and usually united by basal stolons.
3. Only single ventral siphonoglyph present.

Example: Zoanthus, Epizoanthus.

Order 2. Actiniaria

1. Simple, often large-sized , solitary anemones.
2. Body muscular. often with an aboral pedal disc.
3. Skeleton absent.
4. Tentacles and mesenteries are numerious.
5. Siphonoglyphs usually one or two.

Example: Sea-anemones. Metridium, Edwardsia, Adamsia, Actinia.

Order 3. Ceriantharia

1. Long, solitary, anemone-like forms, without pedal discs and skeleton.
2. Tentacles simple, numerous, arranged in two whorls - oral and marginal.
3. Siphonoglyphs single and dorsal.

Example: Cerianthus

Order 4. Antipatharia

1. Colonial and tree like
2. Tentacles and mesenteries comparatively few (6-24) in number.
3. Skeleton as branched, chitinoid axis.
4. Siphonoglyphs two.

Example: Black corals, Antipathes.

Order 5. Madreporaria

1. Solitary or colonial.
2. Exoskeleton hard, compact, often massive, calcareous.
3. Polyps small, living in cup -like cavities on the exoskeleton.
4. Siphonoglyph absent and muscles feeble.

Example: True or stony corals.Flabellum, Fungi, Favin, Oculina.

Subclass 3. Tabulata

Extinct colonial anthozoans with heavy calcareous skeletal tubules containing horizontal platforms or tubules.

Example: Favosites, Halysites.

Reference:

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L.,Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.iaszoology.com/classification-of-coelenterata/

https://en.wikipedia.org/wiki/Coelenterata