Phylum Porifera | Classification, Characters, Examples

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What is the Phylum Porifera?

The term phylum Porifera is derived from Latin. Porifera is derived from the Latin language Poros which means pore. There are many pores on the body of the animal of this association, they are commonly called sponges.

Characters of phylum Porifera –

• A multicellular organism is having a Cellular grade of construction.
• All aquatic exclusively marine but a few freshwaters.
• The plant likes fixed forms with variable body forms.
• Solitary or colonial.
• The body is either symmetrical or radially symmetrical.
• The body surface is perforated by numerous pores, the ostia serving for the inflow of water.  The water current passes through the ostia into the chambers and the central cavity and finally comes out of the body through the terminal aperture The osculum.
• Body wall with outer pinacoderm (dermal epithelium) Inner choanoderm (Gastral epithelium)  and gelatinous Non-Cellular mission mesenchyma in between.
• No definite organ for feeding and digestion. digestion intracellular. The water current serves to bring food organisms and oxygen into the body and carry away the excretory and reproductive products.
• Cells are usually arranged and do not form definite layers. Thus these are not truly diploblastic.
• Choanocytes ( Flagellated collar cells)  usually line special Chambers. Choanocytes are present only in sponges.
• Sensory and Nerve cells are absent but each Cell is directly stimulated and transmutes sensation  To other cells also.
• All sponges are hermaphrodites but cross-fertilization Is a rule.
• Asexual reproduction by  Buds   or  gemmules.
• Sexual reproduction by ova and sperms.
• Sponges have the great power of regeneration.
• Development indirectly through a free-swimming ciliated Larva the amphiblastula or parenchyma.

Classification of phylum Porifera –

Phylum Porifera includes more than 5000  species of sponges grouped into three classes. Recently Bergquist 1978 divided sponges into the following four classes based on the nature and character of the Skeleton.

Classes –

1. Calcarea or Calciospongiae
2. Hexactinellida or Hyalospongiae
3. Demospongiae

Class 1, Calcarea or Calciospongiae –

• The small-size calcareous sponge is below 10 cm in height.
• Solitary or colonial.
• Body cylindrical or vase-like in shape.
• Skeleton formed of calcareous spicules which may be one, three, or four – rayed.
• Body organization may be asconoid, syconoid, or leuconoid type.
• All are marine.
• Class Calcarea has been divided into two orders.

ORDER 1. Homocoela

• Cool and sponges with radially symmetrical and cylindrical bodies.
• Body wall thin and unfolded choanocytes line the spongocoel.
• Often colonial.
• Example – Leucosolenia, Clathrina

ORDER 2. Heterocoela

• Syconoid and leuconoid sponges with thin-walled vase-shaped bodies.
• Choanocytes are found in radial canals or in the flagellated chambers only.
• Solitary or colonial.
• Example – Schypha (Sycon), Garantia.

Class 2. Hexactinellida or Hyalospongiae

• Commonly known as glass sponges.
• Medium size sponge may reach one meter in length.
• Skeleton made of triaxon (six-rayed) siliceous spicules.
• Body cylindrical funnel-shaped or cup-shaped.
• Dermal epithelium absent.
• The Canal system is complicated and body organization is syconoid type.
• Choanocytes are restricted to finger-shaped chambers.
• All marine; many are found in the deep sea. This class has been divided into two orders:

ORDER 1. Hexasterophora

• Spicules star-shaped (six-rayed) i.e. hexasters.
• Amphi Discs are absent.
• Flagellated chambers are regularly and radially arranged.
• Usually attached to substratum directly.
• Examples – Euplectella (Venus’s flower basket), Farnera, Staurocalyptus.

ORDER 2. Amphidiscophora

• Spicules with amphidisc, i.e. with a convex disc bearing backwardly directed marginal teeth at both the ends-hexasters are absent. 
• Attached to the substradium by root length.
• Examples – Hylonema (glass-rope sponge) and Pheronema (bowl sponge).

Class 3. Demospongiae

• Small to large-sized solitary or colonial sponges.
• Body like a cup or vase or compact.
• The skeleton of siliceous spicules or spongin fibers or both.
• Spicules are either monaxon or tetraxon, but never triaxon. These are differentiated into microscleres (small-sized) and macro. Sclerosis or megascleres (large-sized).
• Canal system leuconoid type. The choanocytes are restricted to small rounded chambers.
• All are marine but there is one family of freshwater sponges (Spongillidae).
• The class Demospongiae is divided into three subclasses.

Subclass (1) Tetractinellida

• Spicules are siliceous and tetraxon (four rayed) or absent.
• Spongin fibers are absent.
• Mostly found in shallow water.
• It includes the following three orders:

ORDER 1. Myxospogida

• Both spicules and spongin fibers are absent.
• Structure simple.
• Example – Oscarella, Halisarca.

ORDER 2. Carnosa or Microsclerophora

• Micro and megascleres are indistinct.
• All spicules are monaxons. Tetraxons are absent.
• Example – Chondrilla and Plank.

ORDER 3. Choristida

• Both micro and megascleres are present. Tetraxon spicules with long axes.
• Example – Thea, Geodia.

Subclass (2) Monaxonida

• Spicules are siliceous and monaxon.
• Spongin fibers may be present or absent.
• Mostly occur in shallow water, but some may live in deep sea or in freshwater.

ORDER 1. Hadromarina

• Spongin fibres are absent.
• Megascleres knobed at both ends. These are called tylostyles.
• Microscleres are star-shaped when present.
• Examples – Cliona (boring sponge-that bores in the molluscan shell), Pterion, Donatia.

Order 2 : Halichondrina

• Spongin fibers are very little
• Megascleres of many kinds: usually 2-rayed.
• Microscleres are usually absent.
• Example – Halichondria (crumb of bread sponge)

ORDER 3. Poecilosclerina

• Large spicules or megascleres of many types and united with spongin fibers and form a regular network.
• Microscleres (small spicules) C- shaped, curved or bow-shaped.
• Example – Microciona, Myxitta.

ORDER 4. Haplosclerina

• Megascleres are only of one type, having  2-rays only.
• Microscleres may be present or absent.
• Spongin fibers are present.
• Examples – Chalina (mermaid’s gloves), Spongilla, and Ephydatia.

Subclass (3) Keratosa

• Horny sponges.
• The skeleton contains spongin fibers only.
• Spicules absent.
• Examples – Euspongia (bath sponge), Hippospongia (horse sponge), Hircinia.

Describe briefly the origin of Porifera.

Porifera was once considered to be a colonial protozoan related to the choanoflagellates. evidence in support of this view are:

1. Presence of choanocytes.
2. Method of skeleton production.
3. Lack of farmed tissues.
4. Protozoan mode of feeding.
5. Totipotency of cells.
6. Lack of integration within the sponge body.

 However, most now believe that Sponges had a common origin with other metazoans but diverged early in metazoan history.

There can be little doubt that sponges diverged early from the main line of M zone evolution and have given rise to other members of the animal kingdom.

Because of the Year isolated phylogenetic position the sponges have been placed in a separate subkingdom The parazoa is distinct from other multicellular animals the eumetazoans.

Conclusion

Today, in this article, we know about the Phylum Porifera, its characteristics, and its classification.

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