BSc 1st Year Lower Non-chordates Phylum Porifera Sample Model Practice Question Answer Papers
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BSc 1st Year Lower Non-chordates Phylum Porifera Question Answers
Q.1. Classify phylum Porifera up to orders giving salient features and at least two examples of each group.
Ans.1. Distinguishing Features of Phylum Porifera
1. Multicellular organisms having cellular grade of construction.
2. All aquatic, exclusively marine but a few freshwater.
3. Plant-like, fixed forms with variable body form.
4. Solitary or colonial.
5. Body either asymmetrical or radially symmetrical.
6. Body surface perforated by numerous pores, the ostia, serving for the inflow of water. The water current passes through ostia into the chambers and the central cavity and finally comes out of the body through terminal aperture, the osculum.
7. Body wall with outer pinacoderm (dermal epithelium), inner choanoderm (gastral epithelium), and gelatinous non-cellular mesenchyma in between.
8. No definite organs for feeding and digestion. Digestion intracellular. The water current serves to bring food organisms and oxygen in the body and carry away the excretory and reproductive products.
9. Cells loosely arranged and do not form definite layers. Thus these are not truly diploblastic.
10. Choanocytes (flagellated collar cells) usually line special chambers. Choanocytes are present only in sponges.
11. Sensory and nerve cells absent, but each cell is directly stimulated and transmits sensations to other cells also.
12. All sponges are hermaphrodite but cross fertilisation is a rule.
13. Asexual reproduction by buds or gemmules.
14. Sexual reproduction by ova and sperms
15. Sponges have great power of regeneration.
16. Development indirect through a free-swimming ciliated larva, the amphiblastula or parenchymula.
Phylum Porifera includes more than 5,000 species of sponges grouped in 3 classes. Recently Bergquist, 1978, has divided sponges into the following four classes based on the nature and character of the skeleton :
Class 1. Calcarea or Calciospongiae
1. Small-sized calcareous sponges below 10cm in height.
2. Solitary or colonial.
3. Body cylindrical or vase-like in shape.
4. Skeleton formed of calcareous spicules which may be one, three or four-rayed.
5. Body organisation may be asconoid, syconoid or lenconoid type.
6. All are marine.
Class Calcarea has been divided into two orders:
ORDER 1. Homocoela
1. Asconoid sponges with radially-symmetrical and cylinderical body.
2. Body wall thin and unfolded; choanocytes line the spongocoel.
3. Often colonial.
Examples: Leucosolenia, Clathrina.
ORDER 2. Heterocoela
1. Syconoid and leuconoid sponges with thin-walled vase-shaped body.
2. Choanocytes are found in radial canals or in the flagellated chambers only.
3. Solitary or colonial.
Examples: Schypha (Sycon), Grantia.
Class 2. Hexactinellida or Hyalospongiae
1. Commonly known as glass sponges.
2. Medium-sized sponges; some may reach one meter in length.
3. Skeleton made of triaxon (six-rayed) siliceous spicules.
4. Body cylindrical, funnel-shaped or cup-shaped.
5. Dermal epithelium absent.
6. Canal system complicated and body organisation syconoid type.
7. Choanocytes restricted to finger-shaped chambers.
8. All marine; many found in deep sea. This class has been divided into two orders:
ORDER 1. Hexasterophora
1. Spicules star-shaped (six-rayed) i.e. hexasters.
2. Amphidiscs absent.
3. Flagellated chambers regularly and radially arranged.
4. Usually attached to substratum directly.
Examples: Euplectella (Venus’s flower basket), Farnera, Staurocalyptus.
ORDER 2. Amphidiscophora
1. Spicules with amphidiscs, i.e. with a convex disc bearing backwardly directed marginal teeth at both the ends-Hexasters absent.
2. Attached to the substradium by root length.
Examples : Hyalonema (glass-rope sponge), Pheronema (bowl sponge).
Class 3. Demospongiae
1. Small to large-sized, solitary or colonial sponges.
2. Body like a cup or vase or compact.
3. Skeleton of siliceous spicules or spongin fibres or of both.
4. Spicules are either monaxon or tetraxon, but never triaxon. These are differentiated into microscleres (small-sized) and macroscleres of system or megascleres ( large sized ).
5. Canal system leuconoid type. The Choanocytes are restricted to small rounded chambers.
6. All are marine but there is one family of freshwater sponges (Spongillidae).
Class Demospongiae is divided into three subclasses :
Subclass (1) Tetractinellida
1. Spicules siliceous and tetraxon (four rayed) or absent.
2 Spongin fibres are absent.
3. Mostly found in shallow water.
It includes following three orders :
ORDER 1. Myxospongida
1. Both spicules and spongin fibres are absent.
2. Structure simple.
Examples: Oscarella, Halisarca
ORDER 2. Carnosa or Microsclerophora
1. Micro and megascleres are indistinct.
2. All spicules are monaxons. Tetraxons are absent.
Examples: Chondrilla and Plankia.
ORDER 3. Choristida
1. Both micro and megascleres are present. Tetraxon spicules with long axis.
Examples: Thenea, Geodia.
Subclass (2) Monaxonida
1. Spicules siliceous and monaxon type.
2. Spongin fibres may be present or absent.
3. Mostly occur in shallow water, but some may live in deep sea or in fresh water.
ORDER 1 Hadromarina
1. Spongin fibres absent.
2. Megascleres knobed at both ends. These are called tylostyles.
3. Microscleres star-shaped when present.
Examples: Cliona (boring sponge-that bores in the molluscan shell), Pterion, Donatia.
ORDER 2. Halichondrina
1. Spongin fibres very little.
2. Megascleres of many kinds; usually 2-rayed.
3. Microscleres usually absent.
Examples: Halichondria (crumb of bread sponge)
ORDER 3. Poecilosclerina
1. Large spicules or megascleres of many type and united with spongin fibres and form a regular network.
2. Microscleres (small spicules) C-shaped, curved or bow-shaped.
Examples: Microciona, Myxitta.
ORDER 4. Haplosclerina
1. Megascleres are only of one type, having 2-rays only.
2. Microscleres may be present or absent.
3. Spongin fibres present.
Examples: Chalina (mermaid’s gloves), Spongilla, Ephydatia.
Subclass (3) Keratosa
1. Horny sponges.
2. Skeleton contains spongin fibres only.
3. Spicules absent.
Examples : Euspongia (bath sponge), Hippospongia (horse sponge), Hircinia.