BSc 1st Year Lower Non chordates Phylum Cnidaria Sample Model Practice Question Answer Papers
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BSc 1st Year Lower Non chordates Phylum Cnidaria Sample Model Practice Question Answer Papers
Ans.1. The term Coelenterata includes animals having special stinging cells or nematoblasts. The classification of this phylum is based on the duration of polypoid and medusoid generations.
1. Primitive metazoans having low grade of tissue construction.
2. Aquatic animals, solitary or colonial.
3. Body radially or biradially symmetrical with oral-aboral axis.
4. Exhibit cell tissue-grade of organisation i.e. cells specialised for different functions remain scattered.
5. Body wall diploblastic with an outer layer of epidermis or ectoderm and an inner layer of gastrodermis or endoderm separated by a non-cellular, jelly-like, cementing layer of mesogloea, which may be fibrous with wandering amoebocytes in higher forms.
6. The body wall encloses a single central cavity, the gastrovascular cavity, or the coelenteron. It acts as digestive tube and has a single opening to the exterior, which serv es both for intake of food and ejection of undigested residue, the anus being absent. This opening is called mouth.
7. Mouth is situated on a hypostome and is surrounded by tentacles.
8. These possess batteries of stinging cells or nematocysts that serve for adhesion, offence, defence and food capture.
9. The coelom, excretory, circulatory and respiratory organs are absent.
10. Muscular system includes circular and longitudinal muscle fibres of endothelio-muscular and epithelio-muscular cells respectively.
11. Locomotion is brought about by smooth muscle fibres.
12. Digestion is both extracellular (inside the gastrovascular cavity and intracellular (within nutritive cells of gastrodermis).
13. Nervous system is in the form of diffused network of unpolarised nerve cells in the body wall.
14. Sense organs are ocelli and statocysts.
15. Skeleton either calcereous or horny and external or internal but absent in few.
16. Two types of individuals are found: polyps and medusae.
(i) Polyps are sedentary, cylindrical and asexual.
(ii) Medusae are free-swimming, bell-shaped or umbrella-shaped and sexual.
17. Asexual reproduction by budding or fission and form colonies; sexual reproduction by forming gametes.
18. Development includes free-swimming ciliated planula larva or stereo gastrula larva.
19. Life history exhibits regular alternation of asexual polypoid phase and sexual medusoid phase. This is called metagenesis.
Phylum Coelenterata is divided into three classes based on the presence or absence of polypoid and medusoid phases :
Class 1. Hydrozoa
1. Mostly colonial and marine, a few are fresh-water and solitary.
2. Only polypoid forms or with both polypoid and medusoid forms that exhibit alternation of generations.
3. Polyps simple without stomodaeum, nematocysts, gastric filaments, septa and mesenteries.
4. Medusa with a true velum (Craspedote), but without oral arms.
5. Gonads are epidermal in origin. Sex cells are shed directly to the outside.
6. Mesogloea is non-cellular and jelly-like.
7. Perisarc is the horny, cuticular or calcareous covering outside the body of polyp. It is secreted by epidermal cells.
The class is divided into following orders :
ORDER 1. Hydroidea
1. Polypoid generation well-developed and predominant.
2. Medusa stage short-lived or absent.
3. Mesogloea non-cellular.
4. Sense organs exclusively ectodermal.
5. Freshwater or marine forms; solitary or colonial.
Suborder (1) Anthomedusae or Athecata or Gymnoblastea
1. Hydranths and gonophores without hydrotheca and gonotheca.
2. Medusa bell-shaped.
3. Gonads on the manubrium of medusa.
Examples: Bougainvillia, Hydra, Tubularia, Eudendrium, Hydractinia, Pennaria, Ceratella, Chlorohydra, Protohydra.
Suborder (2) Leptomedusae or Thecata or Calyptoblastea
1. Hydranths and gonophores with hydrotheca and gonotheca respectively.
2. Medusa saucer-shaped
3. Gonads in relation with radial canals of medusa.
Examples: Obelia, Plumularia, Sertularia, Companularia, etc.
ORDER 2. Hydrocorallina
1.Colony with dimorphic polyps, the dactylozooids and gastrozooids.
2. Sexual form is medusa.
3. Polyps with calcareous exoskeleton or corallum, secreted by coenosarc.
Suborder (1) Milleporina
1. Polyps scattered; corallum with separate pores for dactylozooids (small pores) and for gastrozooids (large pores).
2. Medusa very small with four or five tentacles.
Suborder (2) Stylasterina
1. Dactylozooids solid and with tentacles.
2 Gonophores reduced to sporosacs.
3. Medusa not free.
ORDER 3. Trachylina
1. Hydroid phase reduced or absent, medusoid phase dominant.
2. Medusae large, free-swimming and develop from the fertilised eggs.
3. Statocysts with endodermal statoliths.
Suborder (1) Trachymedusae
1. Tentacles inserted above bell margins.
2. Gonads on radial canals.
Examples: Gonionemus, Aglantha, Craspedacusta.
Suborder (2) Narcomedusae
1. Tentacles arise between bell margin and vertex of exumbrella.
2. Gonads present on manubrium or on stomach floor.
Examples: Polycolpa, Cunina, Cunarcha.
ORDER 4. Siphonophora
1. Form large floating (pelagic) colonies.
2. Colony highly polymorphic showing different types of zooids.
3. Polyps and medusae remain attached to a stem.
4. Pneumatophore may or may not be present.
5. All are marine forms.
Suborder (1) Calycophora
1. Pneumatophore absent.
2. Upper end of colony with one or more swimming bells (nectophores).
Examples: Abyla, Diphyes, Praya.
Suborder (2) Physophorida
1. Upper end of colony with a large gas-filled float or pneumatophore.
2. Both polypold and medusold forms present
Examples: Physalia, Halistemma, Stephalia
ORDER 5. Chondrophora
1. Free-floating (pelagic) forming polymorphic polypold colony.
2. Upper end with a chitinous, gas-filled, oval float (pneumatophore).
3. Gonozooids produce free medusae.
Examples: Porpita, Vellela
Class 2. Scyphozoa
1. Exclusively marine and solitary forms.
2. Gastro-vascular cavity with gastric pouches and endodermal gastric filaments but without stomodaeum.
3. Medusa bell-shaped or umbrella-shaped and devoid of velum.
4. Mesogloea cellular and with fibres.
5. Gonads gastrodermal in origin. Sex cells are released in digestive cavity.
6. Gastrovascular cavity without stomodaeum but with gastric pouches.
7. Perisarc is absent.
8. The gonads are endodermal in origin.
9. Exclusively marine.
ORDER 1. Stauromedusae (Lucernarida)
1. Umbrella conical or vase-shaped.
2. Attached to some objects by aboral stalk i.e. (exumbrella peduncle).
3. Tentaculocysts absent.
Examples: Lucernaria, Haliclystus.
ORDER 2. Cubomedusae (Charybdeida)
1. Umbrella cuboidal or four-sided cup-shaped with a false velarium.
3. Tentaculocysts four and per-radial.
ORDER 3. Coronatae
1. Umbrella conical and divided by a horizontal coronary groove.
2. Tentaculocysts four to sixteen.
Examples: Periphylla, Atolla, Pericolpa.
ORDER 4. Semaeostomae (Discomedusae)
1. Umbrella flattened, saucer-shaped or cup-shaped.
2. Tentaculocysts 8, (4 per-radial + 4 inter-radial)
3. Mouth squarish and its corners are produced into four long oral arms.
Examples: Aurelia, Pelagia, Cyanea.
ORDER 5. Rhizostomae
1. Umbrella hemispherical and without marginal tentacles.
2. Tentaculocysts 8 or more in number.
3. Arms bear numerous funnel-shaped mouths along their edges
Examples: Rhizostoma, Cassiopea, Pilema.
Class 3. Anthozoa or Actinozoa
1. Polypoid coelenterates with no medusa phase.
2. Mouth leads into stomodaeum. Oral end expanded into oral disc with tentacles.
3. Gastrovascular cavity subdivided by septa or mesenteries.
4. Mesenteries carry nematocysts and gonads.
5. Mesogloea thick and cellular and in the form of fibrous connective tissue.
6. Ectoderm secretes exoskeleton of CaCO3 or keratin and often forms corals. Endoskeleton is also found.
7 Exclusively marine, majority are coloinal.
Subclass (1) Octocorallia (Alcyonaria)
1. Exclusively marine and colonial.
2. Polyps with 8 pinnately branched tentacles and 8 complete unpaired
3. Only one siphonoglyph.
ORDER 1. Stolonifera
1. Polyps not fused but are connected by the basal stolon.
2. Skeleton of each polyp in the form of a separate tube or absent.
3. Tubes are connected by horizontal platforms.
Examples: Tubipora (Organ pipe coral), Clavularia.
ORDER 2. Telestacea
1. A colony consists of lateral polyps on simple or branched stems arising from a creeping base.
2. Skeleton of calcareous spicules.
ORDER 3. Alcyonacea
1. Soft corals.
2. Colony fleshy and mushroom-shaped or branched into stout blunt processes.
3. Polyps dimorphic-autozooids and siphonozooids.
4. Basal portion of polyps fused to form fleshy part of the colony-coenenchyme.
5. Skeleton formed of unfused calcareous spicules strewn in the colony-coenenchyme.
Examples: Alcyonium, Sclerophyton.
ORDER 4. Coenothecalia
1. Skeleton massive, bluish (blue corals) and formed of crystalline fibres of aragonite fused into lamellae.
2. Skeleton perforated by large and small vertical tubes.
3. Large tubes contain basal part of polyps and small tubes enclose solenial tubes.
Example: Heliopora (blue coral)
ORDER 5. Gorgonacea
1. Branched tree-like forms.
2. Skeleton calcareous or of horny substance-gorgonin, ectodermal in origin.
Examples: Gorgonia, Corallium (red coral).
ORDER 6. Pennatulacea
1. These are called sea pens.
2. Colony elongated and sessile. Lower part embedded in mud, upper part consists of a long, axial polyp with lateral branches bearing dimorphic polyps.
3. Skeleton of calcareous spicules or horny substance,
Examples : Pennatula, Renilla, Pteroeides.
Subclass (2) Zoantharia or Hexacorallia
1. Solitary or colonial.
2. Tentacles and mesenteries numerous but never eight.
3. Gullet commonly with 2 siphonoglyphs.
ORDER 1. Zoanthidea
1. Mostly colonial, some may be solitary.
2. Polyps small and usually united by basal stolons.
3. Skeleton and pedal disc absent.
4. Only single, ventral siphonoglyph present.
Examples: Zoanthus, Epizoanthus, Polythoa.
ORDER 2. Actiniaria
1. Solitary anemones without skeleton.
2. Body muscular, often with an aboral pedal disc.
3. Tentacles and mesenteries numerous.
4. Siphonoglyphs one or two.
Examples: Edwardsia, Metridium, Adamsia.
ORDER 3. Ceriantharia
1. Long, solitary, sea-anemone-like forms with an oral disc but without pedal disc and skeleton.
2. Tentacles simple and numerous, arranged in two whorls: oral and marginal.
3. Siphonoglyph single and dorsal.
ORDER 4. Antipatharia
1. Colonial and tree-like forms.
2. Tentacles and mesenteries comparatively few in number (6-24).
3. Polyps arranged around an axial skeleton.
4. Polyps with two siphonoglyphs.
Examples: Antipathies (black coral).
ORDER 5. Madreporaria
1. Colonial, reef-building stony corals.
2. Colony secretes a heavy, external, calcareous skeleton.
3. Polyps small and enclosed in cup-like depressions in an exoskeleton.
4. No siphonoglyph.
Examples : Fungia, Astraea, Favia, Meandrina, Madrepora.
ORDER 6. Corrallimorpharia
1. Solitary with radially arranged tentacles.
2. Resemble true corals, but without skeleton.
Examples: Corynactis, Ricordea.