17 Representative Types of Coelenterata | Zoology

The following points highlight the seventeen representative types of Coelenterata. The types are: 1. Bougainvillea 2. Physalia 3. Halistemma 4. Velella 5. Porpita 6. Lucernaria 7. Cyanea 8. Rhizostoma 9. Tubipora 10. Gorgonia 11. Corallium 12. Pennatula 13. Renilla 14. Adamsia 15. Fungia 16. Madrepora 17. Astraea.

Coelenterata: Representative Type # 1.

Bougainvillea:

Bougainvillea (Fig. 35.1) is a dimorphic colony; a creeping hydrorhiza gives off branches which produce numerous polyps and medusae. The polyp has a long stalk and a hydranth. The hydranth has a mouth on a manubrium. Just below the manubrium is a ring of tentacles, there is a second ring of larger aboral tentacles around the lower part of the hydranth.

Both kinds of tentacles are solid with an axis of vacuolated endoderm cells. A stiff perisarc covers the hydrorhiza, branches and stalks, but it stops short at the base of the hydranth, and it does not form a hydrotheca. From the coenosarc of the stalk arise several buds, within each bud a single medusa develops. The medusa is like a deep bell, it breaks from the stalk and swims away; there is no blastostyle.

Coelenterata: Representative Type # 2.

Physalia (Portuguese Man-of-War):

Physalia (Fig. 35.2) is a polymorphic colony of bright blue colour. It is found floating in tropical and sub-tropical oceans. The members of the colony arise from the coenosarc. There is a large gas-filled pneumatophore, formed by several medusoids, it floats above the surface, it contains gas glands which produce a gas having 90% nitrogen, 9% oxygen and 1% argon.

In some species, but not in Physalia, the pneumatophore has a pore through which gas can be let out to sink the colony.

Below the pneumatophore hangs a colony of several non-linear cormidia; a cormidium is a group of polymorphic individuals which are modified polyps, they are dactylozooids, gonozooids, and gastrozooids. Dactylozooids are of various sizes, each is a tubular, mouthless individual with a long tentacle having strong muscles and a twisting ribbon of nematocysts.

Dactylozooids may be up to 12 metres long, they form a drift net for capturing fish for food, the tentacles pull them up.

Gastrozooids are tubular with a mouth and a long tentacle may be present. The lips of gastrozooids are applied to the fish and partly digested food is sucked up in liquid form. Gonozooids or gonodendra are branching blastostyles having leaf-like gonopalpons and male and female medusae or gonophores.

The female gonophores are degenerate, they are set free for a short time, the male gonophores are degenerate but are permanently attached.

The germ cells form a planula larva which gives rise to a new colony. The pneumatophore and gonophores are modified medusoids. A small fish Nomeus lives near the deadly tentacles in a commensal relationship with Physalia. The members of the colony of Physalia show a division of labour and, thus, simulate the organs of Metazoa.

Coelenterata: Representative Type # 3.

Halistemma:

Halistemma (Fig. 35.3) is a polymorphic colony consisting of a long, slender, floating stem to which polymorphic zooids are attached along its length.

The upper end of the stem has a small pneumatophore which is like an invaginated cup, it is gas-filled. Below the pneumatophore are several closely set nectocalyces or swimming bells, they are transparent and look like medusae without manubria, but they have a velum, muscles and canals.

Nectocalyces contract rhythmically to take in water and pump it out at once by which they propel the colony in sea water. Below the nectocalyces on the stem are several cormidia in groups one after another in a linear series. A cormidium has a gastrozooid, dactylozooid, hydrophyllium and gonozooids. Gastrozooid is tubular with a mouth and a tentacle which is long and branched and bears numerous nematocysts.

Dactylozooid is tubular with no mouth, but an unbranched tentacle which is sensory. Gonozooids or sporosacs lie in groups, they bear male and female medusae or gonophores. Hydrophyllium is a shield-shaped leaf which covers and protects the rest of the cormidium. The upper end is the proximal end, it corresponds to the attached end of Obelia.

Coelenterata are radially symmetrical, but Halistemma shows bilateral symmetry. Germ cells form a zygote which develops into a planula, one end of the planula invaginates to form the pneumatophore, while the lower end forms a polyp, this first polyp by elongation and budding forms the colony.

Coelenterata: Representative Type # 4.

Velella:

Velella (Fig. 35.4) is a polymorphic colony which looks like a single medusa. It has a rhomboidal body on whose upper surface is an oblique sail. Dorsally there is a pneumatophore like a chitinous chambered disc which contains air, the chambers communicate with the exterior. From the middle of the body hangs a single large gastro-zooid having a mouth.

All around the gastrozooid are numerous gonozooids or blastostyles, each having a mouth, they produce free-swimming medusae. On the margin of the body is a circle of long tentacle-like dactylozooids having nematocysts.

In the body are numerous ramifying canals of ectodermal and endodermal origin, the endodermal canals communicate with the enteron of gonozooids and gastrozooid, while the ectodermal canals open into the chambers of the pneumatophore.

The pneumatophore and its sail are a modified medusoid, but the gastrozooid, gonozooids, and dactylozooids are modified polyps, Velella is found along the Southern Atlantic coast where the colony is carried about by the wind.

Coelenterata: Representative Type # 5.

Porpita:

Porpita (Fig. 35.6) is a polymorphic colony allied closely to Velella. The colony resembles a medusa. It has a large disc-like body with a chitinous, chambered pneumatophore containing air each chamber communicates with the exterior by two pores.

From the body, hangs a single gastrozooid, numerous tubular gonozooids or blastostyles bearing medusae, and many long marginal dactylozooids with nematocysts. Body has ramifying canals, some open into the pneumatophore, while others communicate with the enteron of zooids.

Coelenterata: Representative Type # 6.

Lucernaria:

Lucernaria (Fig. 35.7) is a sessile, marine Scyphozoa found in the British coasts. Body is trumpet-shaped provided with an aboral stalk by which it is attached to sea weeds and other objects. The margin of the umbrella is divided into eight short and hollow ad-radial lobes.

Each lobe bears a group of short knobbed hollow tentacles at its end. Mouth is cruciform (four-cornered) with small oral lobes and a short manubrium. Gastro vascular system consists of a central stomach and four per-radial pouches divided by four inter-radial septa. Gastric filaments are numerous. Gonads are band-like borne on the septa. Marginal sense organs or tentaculocysts and velum are absent.

Coelenterata: Representative Type # 7.

Cyanea:

Cyanea (Fig. 35.8) is a common jelly-fish found in coastal waters of America and also extend in the polar regions. The disc or umbrella is usually 5 to 40 cm in diameter but the largest species Cyanea arctica may reach up to 2 metres in diameter. The’ umbrella is saucer or bowl-like with its margin scalloped into eight lappets. It is purple and red in colour. Each lappet contains a rhopalium in its niche.

Eight tentacles are arranged in V-shaped clusters arising from the sub-umbrella ad-radially. Mouth is four cornered situated in the centre of sub-umbrella.

The four corners of the mouth extend into four very long frilly oral arms. Four large bunches of gonads are situated between the oral arms and tentacles. Numerous radial canals branch into the rhopalia and tentacles near the margin. Ring canal is absent. Cyanea arctica is commonly known as sea blubber.

Coelenterata: Representative Type # 8.

Rhizostoma:

Rhizostoma (Fig. 35.9) is a large jelly-fish found in the shallow waters of Indo-Pacific region.

It has a saucer-shaped umbrella with a scalloped margin having eight or sixteen tentaculocysts in different species, there are no marginal tentacles. In a young Rhizostoma there is a central mouth, but in the adult the mouth is closed by the overgrowth and folding of four oral arms, and it is replaced by thousands of pore-like sectorial mouths which lie along the closed grooves of oral arms, they are connected to the canals.

The oral arms become organs of external digestion, they digest the food and the fluid is absorbed by sucking mouths.

This polystomatous (many-mouthed) condition is unique in animals. Oral arms are bifurcated distally to form eight long, club-shaped terminal appendages. Tentacles lie only on oral arms in two groups, they look like filamentous roots and bear nematocysts. Additional mouth-bearing outgrowths called scapulets occur on the oral arms just below the bell.

Coelenterata: Representative Type # 9.

Tubipora:

Tubipora (Fig. 35.10) is commonly known as organ pipe coral. Elongated polyps lie parallel to each other, their internal skeleton made of fused spicules, from mesogloea forms erect parallel tubes which arise from-a basal plate and are joined by calcareous platforms. Polyps lie in the tubes partly projecting above. Polyps are green and the skeleton is dark red due to iron salts. Tubipora is widely distributed on coral reefs.

Coelenterata: Representative Type # 10.

Gorgonia:

Gorgonia (Fig. 35.11) is commonly known as sea fan. It forms large, upright lattice-like branching colonies of yellow and red colour, they are up to 50 cm in height. The colony is fixed by a basal plate from which branches arise in one plane only. The branches anastomose in some species.

Branches bear slender polyps with eight pinnate tentacles. Branches are joined by cross connections in G. flabellum, but in G. verrucosa, there are no cross connections. The skeleton is not calcareous but is made of a horny protein called gorgonin around which the mesogloea forms calcareous spicules.

The skeleton is secreted by the outer surface of the animal but it appears internal. Within the mesogloea is a network of branching tubes called solenia which are tubular extensions of enteron carrying water, oxygen, and food. The sexes of colonies are separate. Sea fans flourish in shallow tropical seas forming plant-like grooves and thickets in the sea near Malaya, West Indies, and Indo-Pacific Ocean.

Coelenterata: Representative Type # 11.

Corallium:

Corallium rubrum (Fig. 35.12) is commonly known as red coral. It is an upright branching colony. Spicules from mesogloea are compacted with a cement-like substance to form a hard axial skeleton which is the precious red coral of commerce.

The skeleton is covered by a delicate coenosarc which has two kinds of polyps:

(a) Autozooids are normal nutritive polyps with eight pinnate tentacles and mesenteries, they bear gonads,

(b) Siphonozooids have no tentacles, mesenteries are reduced, they are small and pump water into the canals of the colony; thus, Corallium is a dimorphic colony. It is found near Japan and in deep Mediterranean. It is highly valued as it is used for making jewellery.

Coelenterata: Representative Type # 12.

Pennatula:

Pennatula (Fig. 35.13) is commonly called sea pen. It forms a quill-like bilaterally symmetrical colony which looks like a fern frond. The central stem is a huge axial polyp. It has a lower peduncle and a distal rachis. The stem contains an unbranched horny skeletal rod, an enteron cavity, and mesogloea within which are solenia as tubular extensions of the enteron.

The peduncle is buried in sea mud by an enlarged end bulb, by peristaltic contractions of the peduncle sea pens can burrow in the mud and even change their position.

The rachis bears lateral branches, the branches are formed by nutritive polyps called anthocodia lying side by side in rows on each side of the rachis with their bases fused together in one plane and inserted diagonally into the sides of the rachis, they give the colony a feather-like appearance. Autozooids have tentacles, mesenteries and gonads.

On the back of the rachis, lying in two zones are reduced polyps called siphonozooids, they have no tentacles, their mesenteries are reduced, but their siphonoglyphs are enlarged, they cause circulation of water in the canals of the colony. The skeleton has a horny axis in the stem, and calcareous spicules in the mesogloea, there is no axis in the branches.

Pennatula sulcata has a bright orange-red colour, some species may be 3 metres long. It is found in the warm coast of the Atlantic and Pacific Oceans.

Coelenterata: Representative Type # 13.

Renilla:

Renilla (Fig. 35.14) is commonly called sea pansy. Colony consists of a short peduncle which is embedded in the mud and a circular kidney-shaped (reniform) leaf-like rachis. Rachis is broad on the ventral surface and devoid of polyps. The dorsal surface is pink or violet in colour and covered with white zooids or polyps.

The colony is dimorphic, bears two kinds of zooids:

(i) Autozooids or anthocodia are scattered irregularly on the dorsal surface and nutritive in function,

(ii) Siphonozooids are arranged in clusters and maintain the circulation of water within the colony. A median bare track devoid of polyps extends from the peduncle to about the middle of the rachis where it terminates at a special exhalent siphonozooid. An axial skeleton is entirely absent. Renilla is a colonial form and occurs in shallow waters of coasts of North and South Carolina and West Indies.

Coelenterata: Representative Type # 14.

Adamsia:

Adamsia (Fig. 35.15) is found attached to the empty shells of gastropods inhabited by hermit crab, Eupagurus, Body is large cylindrical and divisible into three distinct regions, the pedal disc, column and oral disc. Pedal disc is flat, sucker-like and bilobed by which it is attached to the molluscan shell.

Column is cylindrical bears a band of cinclidal tubercles at its base. Two siphonoglyphs and six pairs of mesenteries are present. Oral disc bears a central mouth surrounded by large number of tentacles.

Adamsia furnishes a good example of commensalism (mutual benefit). Adamsia protects the hermit crab from the attacks of its enemies by covering the body and stinging by means of nematocysts.

On the other hand, Adamsia gets the advantage of transportation from one place to another by hermit crab and also receives variety of food supply. This kind of partnership between individuals of two different species is known as commensalism.

Coelenterata: Representative Type # 15.

Fungia:

Fungia (Fig. 35.16) commonly known as mushroom coral, is solitary found in warm seas usually in Gulf of California.

The mushroom coral is of large size, with discoidal corallite, convex on the upper and concave on the lower surface, Septa are numerous and connected together by small synaptacula. Theca is present only on the lower surface. Adult animal bears a single large polyp with many tentacles. Siphonoglyph absent. Reproduction resembling more or less transverse fission.

Coelenterata: Representative Type # 16.

Madrepora:

Madrepora (Fig. 35.17) commonly known as horn coral is colonial and found in Australian seas. Colony is branched with small polyps in cylindrical cups separated by perforated coenosteum. Terminal polyps bear six tentacles, while lateral polyps bear twelve tentacles. Mesenteries are bilaterally arranged. Madrepora is economically important because it takes part in the formation of coral reefs.

Coelenterata: Representative Type # 17.

Astraea:

Astraea (Fig. 35.18) is a massive stony coral found on the coasts of warm seas. The colony comprises numerous closely fitted polygonal cups or theca.

Theca are so closed to each other as to have common walls. Skeleton is very hard made up of calcium carbonate and is secreted by the ectoderm for support of delicate tissues. The colony is formed by buds. The coenochyme is produced by calcification of coenosarc and also gives rise to corallites which lie in close contact to each other.