Q.1. Write the classification of phylum porifera upto classes and add a note on the importance of spicules in classification. (2005)
Related Questions -
Q. Write classification of phylum porifera upto classes with characteristic features. (2018)
Ans. Classification of Phylum Porifera: -
Class I Calcarea: -
(1) Small sized calcareous sponges, never exceeding 10cm in height, solitary or colonial.
(2) Body shape cylindrical or base like.
(3) Skeleton of separate calcareous spicules, one or three or four rayed.
(4) Body organization of asconoid, syconoid on leuconoid type.
(5) Exclusively marine.
Class II Hexactinellida: -
(1) Moderate sized glass sponges some reach 1 meter in length.
(2) Skeleton of six rayed triaxon siliceous spicules.
(3) No dermal epithelium or exopiracodesm.
(4) Choanocytes restricted to finger-shaped chambers.
(5) Exclusively marine, many in deep sea.
Class III Desmospongiae: -
(1) Small to large sized, solitary or colonial.
(2) Skeleton absent on of silecous spicules or of spongin fibres or of both.
(3) Silecous spicules monotone or six rayed.
(4) Body shape vase like, cuplike or cushion like.
(5) Body organization leuconoid, choanocytes restricted to small rounded chambers.
(6) Montly marine, some fresh water.
Importance of Spicules in Classification: -
Class Demospongea: -
These Sponges are present with skeletons of spongin, and siliceous spicules, or a skeleton of fused opaline silica. When present, spicules are commonly monaxon, tetraxon, or polyaxon, but never triaxon.
Class Hexactinellida (Previously Hyalospongae): -
Sponges with siliceous spicules that are usually triaxons and commonly fused to form a net or box-like pattern. They are often called glass sponges.
Class Calcarea: -
Sponges that have calcareous spicules as in Astaeospongia (the disc shaped fossil in the following image) or more commonly, non-spicular porous chambers (the other three fossils in the image). When spicules are present, they are not fused and are typically monaxons and/or tetraxons.
“Class Stromatoporoida”: -
The sheet-like or hemispherical skeletons of stromatoporoids are of two types. The first type have small mounds called mamelons from which canals called astorhizae radiate. This group has horizontal partitions called laminae and vertical partitions called pillars. The space between the laminae and pillars is called the gallery.
The second type of stromatoporoid is similar to the first in having laminae and possibly pillars, yet it lacks the astorhizae and mamelons. This form is quite similar to algal stromatolites, but differ in possessing a true calcareous skeleton.
various types of spicules
Q.2. Giving salient features of phylum porifera, classify it upto classes, with suitable examples. (2013)
Ans. 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 inflew 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.
Classification: -
Recently Bergquist, 1978, has divided sponges into following four classes based on the nature and character of 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:
Order1. Homocoela: -
1. Asconoid sponges with radially - symmetrical and cylindrical 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.
Example: - 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.
Example: - Hyalonema (glass-rope sponge), Pheronema (bowl sponge).
Order 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 or megasclleres (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).