Coelenterata : General Characters and Classification

Coelenterata : General Characters and Classification

GENERAL CHARACTERS:

1. The cell-tissue grade of body organization with most of the cells scattered and specialized for different functions and some forming a tissue, like a nervous tissue or nerve net.

2. All aquatic, some in fresh water, but mostly marine.

3. Solitary or colonial, sedentary or free swimming. 4. Radial or biradial symmetry about a longitudinal oral-aboral axis.

5. Two types of individuals, free or attached polyp and free-swimming medusa. 

6. Body wall diploblastic with two cellular layers-outer epidermis and inner gastro dermis-with a gelatinous mesogloea in between. In some, mesogloea with cells and connective tissue.

7. The inner gastrovascular cavity often branched and divided by mesenteries (septa) and with only one opening, the mouth; mouth often encircled by short and slender tentacles.

8. One or both body layers with peculiar stinging cell organelles, called nematocysts, very abundant on tentacles.

9. Nerve net of spnaptic or non-synaptic pattern with diffuse conduction; sensory organs simple or complicated, some with ocelli and statocysts.

10. Muscular system of epithelio and endothelio muscle cells. In some, independent fibres in the mesogloea.

11. Digestion intra as well as extracellular. 

12. Respiratory, circulatory and excretory systems wanting. 

13. Asexual reproduction by budding or fission; sexual reproduction by gametes. Sexual forms monoecious or dioecious; development exhibits plamla larva. 

14. Life history commonly jillustrates alternation of generations or metagenesis, in which a sexual, free medusoid generation alternates with an asexual, sessile usually colonial, polypoid generation.

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CLASSIFICATION:

Class: 1. Hydrozoa

(Gr., hydra, water+zoios, animal) 

1. Solitary or colonial.

2. Either only polyps or asexual polyps and sexual medusae. 

3. Hydranths without pharynx and septa or mesenteries. 

4. Medusae with true velum.

5. Gonads epidermal.

6. Freshwater or marine; sessile or free.

Order: 1. Hydroida

1. Solitary or colonial. 

2. Polypoid stage predominant.

3. Medusa stage present or absent: when present, short-lived. 

4. Sense organs of medusa exclusively ectodermal (epidermal).

Suborder: I . Anthomedusae

(=Gymnoblastea)

1. Polyp or blastosyle athecate, i.e., perisarc not forming hydrotheca or gonotheca.

2. Medusa with gonads on manubrium.

3. With ocelli; no statocysts. 

4. Freshwater or marine.

Examples: Hydra, Chlorohydra, Pelmato hydra, Tubularia, Clava, Bougainvillea, Pennaria,Podocoryne.Eudendrium, Hydractinia,

Suborder: II.Leptomedusae 

(-Calyptoblastea)

1. Polyp as well as blastostyle thecate, i.e., with hydrotheca and gonotheca, respectively.

2. Medusa with gonads on raidal canals. 

3. Usually with statocysts or eye-spots.

4. Marine.

Examples: Obelia, Sertularia, Campanu laria, Phumularia, Abietineria, Polyorchis.

Suborder: III. Limnomedusae

1. Polypoid stage witout perisarcal skeleton. 2. Some only with medusa stage.

3. Freshwater.

Examples: Craspedocusta (a hydroid), Gonionemus (a medusoid).

Order: 2. Trachylina

1. Medusoid stage dominant; no or poorly developed polypoid generation.

2. Medusa large, large, free swimming and develops directly from fertilized egg. 

3. Medusa bears marginal sense organs such as statocysts or endodermal statoliths. 

4. Gonads on radial canals or on floor of gastric cavity. 

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Suborder: I . Trachymedusae

1. Marginal tentacles oral.

2. Gonads on radial canals.

3. Tentaculocysts in pits or vesicles.

4. Manubrium present. Examples: Liriope, Aglantha. 

Suborder: II . Narcomedusae

1. Marginal tentacles oral.

2. Gonads on stomach floor. 

3. Tentaculocysts naked.

4. No manubrium.

Examples: Cunina, Cunoctantha. 

Suborder: III .Pteromedusae

1. Body elongated along oral-aboral axis. 

2. Four equatorial swimming flaps, each with two statocysts.

3. Nematocysts atrichous isorhizas.

Example: Tetraplaria. 

Order: 3. Hydrocorallina

1. Fixed and colonial.

2. Exoskeleton calcareous.

3. Polyps gastrozooids or nutritive and dactylotooids for capturing prey and protrude through pores in surface layer of the exoskeleton.

4. Sexual form medusa.

Suborder: I. Milleporina

1. Polyps scattered.

2. Separate pores for gastrozooids and dactylozooids.

3. Medusa free, minute and simple, with four or five tentacles.

Example: Millepora. 

Suborder: II . Stylasterina

1. Polyps arranged in systems.

2. Calcareous exoskeleton branching encrusting.

3. Tentacle-free dactylozooids surround the gastrozooids. 

4. No medusa.

Example: Stylaster.

Order: 4. Siphonophora

1. Pelagic and colonial, colony highly polymorphic.

2. Individuals polypoid and medusoid and of several kinds. 

3. A pneumatophore or swimming bell helps in floating of the colony. 

4. Perisarc absent. 

5. Largely in warm seas.

Suborder: I. Calcophora 

1. No pneumatophore.

2. Nectocalyces at the upper end.

3. Individuals polypoid and medusa. 

Examples: Praya, Abyla, Diphyes.

Suborder: II .Physophorida 

1. Pneumatophore at the upper end.

2. Individuals polypoid and medusoid. 

Examples: Physalia of war), Nectalia (Portuguese-man)

Suborder: III .Chondrophora 

1. Pneumatophore at the upper end.

2. Only polypoid individuals. 

Examples: Velella, Porpita.

Class: 2. Scyphozoa

(Gr., skyphos, cup+zolos, animal)

1. Solitary and medusoid.

2. Polypoid stage reduced or absent.

3. Bell or umbrella-shaped medusa without velum.

4 Much enlarged gelatinous mesogloca with fibres and cells.

5. Margin of bell with eight notches bearing sense organs. 

6. Exclusively marine.

Order: 1. Stauromedusae 

(=Lucernariida) 

1. Sessile, attached by a stalk aborally. 

2. Bell, goblet or trumpet-shaped.

3. Tentacles perradial and interradial; no thopalia.

4. A pharynx or stomodacum suspended by four septa. 

5. No alternation of generations 

6. Chiefly in cold littoral water

Examples: Lucernaria, Haliclysmus. 

Order: 2. Cubomedusae 

(=Carybdeida)

1. Bell cubical with four flattened sides and simple margins.

2. Tentacles interradial; four perradial rhopalia.

3. Gastrovascular septa present.

4. No alternation of generations

5. In tropical and subtropical oceans. 

Examples: Charybdea, Chiropsalmus.

Order: 3. Coronatae

1. Bell conical with transverse constriction (coronary groove). 

2. Tentacles perradial and adradial; four interradial rhopalia.

3. A pharynx or stomodaeum suspended by four septa. 

4. No alternation of generations. 

5 Many deep sea species.

Examples: Periphylla, Atolla, Nausithoe.

Order: 4. Semaeostomae 

1. Bell disc-shaped.

2. Tentacles inter radial, perradial, adradial and subradial; four or more perradial and four or more interradial thopalia.

3. Mouth quadrate with four oral lobes. 

4 No gastric pouches or septa.

5. In all oceans of the world. 

Examples : Aurelia, Pelagia, Caynea, Chrysaoro.

Order: 5. Rhizostomac

1. Bell margin with no tentacles,

2. Typically eight rhopalia. 

3. Central mouth obliterated by growth across it of eight very large and branched oral arms bearing numerous funnel-shaped mouth on their edges.

4. No septa.

5. In tropical and subtropical water.

Examples: Rhizostoma, Cassiopea, Mas rigias, Stomolophus.

Class: 3. Anthozoa 

(-Actinozoa) (Gr., anthos, flower+zoios, animal) 

1. Solitary or colonial.

2. All polyps, no medusae,

3. Mouth leads into pharnyx or stomodacum.

4. Gastrovascular cavity subdivided by eight or less or more septa or mesenteries.

5. Mesenteries with nematocysts gonads.

6. Exclusively marine.

Subclass: 1. Octocorallia 

(Alcyonaria) 

1. Exclusively colonial.

2. Polyps with pinnate tentacles,

Order: 1. Stolonifera

1. Polyps arising from a creeping mat or stolon.

2. Skeleton absent or of calcareous tubes or separate calcareous spicules. 

3. In temperature and tropical oceans, in shallow water. 

4. Found on coral reefs in old and new worlds.

Examples. Tubipora, (organ pipe coral). Clavularia.

Order: 2. Telestacea

1. Lateral polyps on single or branched stems. 

2. Skeleton of calcareous spicules.

Example: Telesto. 

Order: 3. Alcyonacea

1. Polyps embedded in fleshy coenenchyme. 

2. Colony massive lobate. or mushroom-like

3. Skeleton of separate calcareous spicules. 4. Largely tropical.

Examples: Soft corals-Alcyonium, Ger semia.

Order: 4. Coenothecalia

1. Polyps brown.

2. Skeleton massive, calcareous and blue-green from iron salts. 

3. In Indo-Pacific waters.

Example: Heliopora (blue coral).

Order: 5. Gorgonacea

1. Colony usually of plant-like branching form bearing short polyps.

2. A central skeletal axis composed of a horn like organic matter, gorgonin. Separate or fused calcareous spicules may be present.

Examples: Horny corals-Gorgonia (sca fan), Corallium (red coral).

Order: 6. Pennatulacea

1. Colony is usually elongated and made of two parts. The lower part of stalk is embedded in the mud of the sea bottom. The upper part or rachis consists of a very long axial polyp with lateral branches bearing dimorphic polyps.

2. Stem is supported by an axial skeleton of separate calcareous spicules or horny substance.

Examples: (Sea pens, Sea pansies), Pennatula, Pteroeides, Renilla. 

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Subclass: 2. Hexacroallia 

(=Zoantharia)

Order: 1. Zoanthidea 

1. Solitary or colonial, mostly epizoic. 

2. Without skeleton and pedal disc but body wall may contain foreign calcareous bodies.

3. Polyps small and usually united by basal stolons. 

4. Only single ventral siphonoglyph present.

5. Pairs of mesenteries mostly composed one complete and one incomplet mesentery. 

Examples: Zoanthus, Epizoanthus.

Order: 2. Actiniaria 

1. Simple, often large-sized solitary and brightly coloured, sessile but not fixed. 

2. Skeleton absent.

3. Body muscular, often with an aboral pedal disc.

4. Tentacles and mesenteries are numerous. 5. Siphonoglyps usually one or two.

Examples: (Sea-anemones), Metridium, Edwardsia, Adamsia, Actinia, Urticina.

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. 

4. Mesenteries numerous, single and complete. 

Example: Cerianthus.

Order: 4. Antipatharia 

1. Colonial and tree-like.

2. Tentacles and mesenteries comparatively few (6-24) in number. 

3. Skeleton composed of a branched, chitinoid axis derived from ectoderm

4. Siphonoglyphs two. Example: (Black corals), Antipathes.

Order: 5. Madreporaria

1. Solitary or colonial

2. Ectoderm secretes a hard, compact, often massive, calcareous exoskeleton. 

3. Polyps small or minute, living in cup-like cavities on exoskeleton.

4 Siphonoglyph absent aud muscles feeble. 

Examples: (True or stony corals), Flabellum, Fungia,(mushroom coral), Astran gia, Astraea (star coral), Favia, Oculina, Acropora (=Madrepora), Meandrina or Meandra (brain coral).

Subclass: 3. Tabulata

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

Examples: Favosites, Halysites.

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