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 –

  • The body of multicellular organisms is made of cellular grade.
  • All aquatic animals are found only in brackish water or in seawater. But some animals are also found in freshwater.
  • They are in definite form like a plant with a changing body.
  • They are solitary or colonial animals.
  • Their body is either asymmetric or radially symmetrical.
  • There are many pores on the surface of their body, and this hole is for water to come in, and this ostia acts as an inward flow for the water. Water enters the chamber through the ostia. It then reaches the central cavity from the chamber and is finally ejected through the osculum, the last orifice of the body.
  • Their body wall is accompanied by pinacoderm (dermal epithelium) on the outside, choanoderm (gastral epithelium) on the inside, and a thin noncellular mesenchyma in between.
  • They do not have fixed organs for food and digestion. Digestion in these is intracellular.
  • In these, the water current serves to bring food organisms and oxygen into the body and carry forward the products of excretion and reproduction.
  • These cells are loosely arranged, and they are not in the form of fixed layers. Hence, they are not properly diploblastic.
  • Choanocytes are mainly specialized lined cells. Choanocytes are present only in sponges.
  • They do not have sensory and nerve cells. But each cell is directly stimulated and transmits the sensations to other cells as well.
  • All sponges are hermaphrodites, but cross-fertilization is a rule.
  • In these asexual reproduction occurs by buds or gemmules.
  • In these sexual reproduction takes place by ovum and spermatozoa.
  • Sponges have the great power of regeneration.
  • The development of a free-swimming ciliate larva occurs indirectly through the amphiblastula or parenchyma.

Classification of phylum Porifera –

The three classes of the phylum Porifera include more than 5000 species of sponge groups. Recently, the scientist Bergquist 1978 divided the sponges into three classes based on their nature and skeletal features, which are as follows.

phylum porifera
Red Tube Sponge images source – Wikimedia commons

Classes –

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

Class 1, Calcarea or Calciospongiae –

  • Calcareous sponges are small in size, and their height is less than 10 cm.
  • They are solitary or colonial.
  • Their body is cylindrical or pitcher-shaped.
  • Their skeleton is made up of calcareous spicules containing calcium. Which is made up of one, three, or four rayed.
  • Their body organization may be of asconoid, syconoid, or lenconoid type.
  • All these are found in seawater.
  • Class Calcarea is divided into two orders.

ORDER 1. Homocoela

  • The conoid sponge has a body in the form of a radius symmetrical and cylindrical.
  • Their body wall is thin and unfolded, choanocytes are lined in sponges.
  • These are often colonial.
  • Example – Leucosolenia, Clathrina

ORDER 2. Heterocoela

  • The body of these sponges is syconoid and leuconoid with a thin wall and pitcher shape.
  • Choanocytes have radial grooves or only flagellated chambers.
  • They are solitary or colonial.
  • Example – Schypha (Sycon), Garantia.

Class 2. Hexactinellida or Hyalospongiae

  • They are commonly known as glass sponges.
  • These sponges are of medium size, and some sponges reach up to 1 meter in length.
  • Their skeleton is made of spicules containing Triaxon (six-rayed) silica.
  • Their body is cylindrical, funnel-shaped, or cup-shaped.
  • They do not have dermal epithelium.
  • Their tubule system is complex, and their body organization is of syconoid type.
  • Choanocytes are confined to finger-shaped chambers.
  • All are marine. Most are found in the deep sea. This class is divided into two orders.

ORDER 1. Hexasterophora

  • Their spicules are six-rayed. That’s why they are called hexasters.
  • Amphidiscs are absent.
  • The flagellated chamber is arranged regularly and radially.
  • Mainly it is directly attached to the base or foundation.
  • Examples – Euplectella (Venus’s flower basket), Farnera, Staurocalyptus.

ORDER 2. Amphidiscophora

  • Amphidisc has convex discs with posteriorly directed edge teeth at both ends, in which Hexasters are absent.
  • It is attached to the base by the length of the roots.
  • Examples – Hylonema (glass-rope sponge) and Pheronema (bowl sponge).

Class 3. Demospongiae

  • These sponges range in size from small to large and are solitary or colonial.
  • Their body is like a cup or a vase or a compact.
  • Their skeleton is made up of silica-rich spines or spongy fibers or both.
  • The thorn is either a monaxon or a tetraxon, but is never a triaxon. These are differentiated into microscleres (small size) and macroscleres or megascleres (large size).
  • Their placental system is of leuconoid type. Choanocytes are restricted by small circular cells.
  • All are marine, but sponges of one family live in freshwater, named Spongillidae.
  • The class Demospongiae is divided into three subclasses.

Subclass (1) Tetractinellida

  • The spines are silica-rich and made of tetraxon (four rays), or absent.
  • They do not have spongin fibers.
  • They are mainly found in shallow water.
  • It is included in three orders.

ORDER 1. Myxospogida

  • It lacks both spines and spongin fibers.
  • Their structure is simple.
  • Example – Oscarella, Halisarca.

ORDER 2. Carnosa or Microsclerophora

  • These micro and megascleres are obscure.
  • All spines are monaxons, tetraxons are absent.
  • Example – Chondrilla and Plank.

ORDER 3. Choristida

  • It contains both micro and megascleres. Along the long axis is the tetraxon.
  • Example – Thea, Geodia.

Subclass (2) Monaxonida

  • The spines are silica-rich and of monaxon type.
  • The spongin filament may be present or absent.
  • It is mainly found in shallow water, but some live in deep sea or in fresh water.

ORDER 1. Hadromarina

  • They do not have spongin fibers.
  • Megascleres have knots at both ends, it is called Tylostyles.
  • Microscleres when present. It is shaped like a star.
  • Examples – Cliona (boring sponge-that bores in the molluscan shell), Pterion, Donatia.

Order 2 : Halichondrina

  • The spongin fibers are very small.
  • There are many types of Megascleres. These are mainly 2-rayed.
  • Microscleres are mainly absent.
  • Example – Halichondria (crumb of bread sponge)

ORDER 3. Poecilosclerina

  • They have large thorns or there are many types of megascleres. and are organized along with the spongin filament. and occurs as a regular mesh.
  • Microscleres (small spines) are C-shaped, bent, or bow-shaped.
  • Example Microciona, Myxitta.

ORDER 4. Haplosclerina

  • Megascleres are of only one type. They only have 2-rayed ones.
  • Microscleres may be present or absent.
  • Spongin fiber is present.
  • Examples – Chalina (mermaid’s gloves), Spongilla, and Ephydatia.

Subclass (3) Keratosa

  • These are arousal sponges.
  • Their skeleton consists only of sponges.
  • The spines are absent in them.
  • Examples – Euspongia (bath sponge), Hippospongia (horse sponge), Hircinia.

Conclusion

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

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