Phylum – Porifera – (Pore-bearing)
Introduction: The porifers are commonly known as sponges. Porifers consisting the most primitive multicellular animals. These are pore-bearing animals, the body does not consist of organs and they can regenerate their lost parts.
The phylum includes around 5ooo species. These are the first multicellular animals. They are called sponges because of their spongy appearance. They show a symbiotic relationship with algae.
Characteristic features of phylum Porifera:
- Habitat: The members of this phylum are generally marine and some are found in freshwater.
- Level of Organisation: Cellular level of organization. (These are primitive Multicellular animals). The cells are loosely organized.
- Symmetry: these are found mostly in asymmetrical animals.
- Water transport or canal system –
- Sponges consist of Water transport or canal system, water enters through a pore called Ostia.
- From Ostia, the water goes to the body wall into the central cavity that is called spongocoel from here the water goes out through the osculum.
- The function of the pathway of the water transport system
- This water transport pathway helps gather food.
- Respiratory exchange
- Removal of waste
- Choanocytes or collar cells: These function to line the spongocoel and canals.
- Digestive system: In sponges, They exhibit holozoic nutrition. The digestive system is found intracellular.
- Intracellular digestion: Breakdown of food or energy-providing substances within the cell.
- Skeleton: In Sponges, the body is supported by a skeleton. The skeleton is made up of Spicules or spongin fibers.
- Sexes: These are hermaphrodites (sexes are not separate), i.e. sperm and eggs are produced by the same individual.
- Indirect development is found in sponges during the larval stage and adult stages. The larval stage in porifers is morphologically distinct from the adult stage. The larva is ciliated and free-swimming, called parenchymulla and amphiblastula.
- Sponge Cliona is detrimental to the pearl industry
- Spongiolla is an example of a freshwater sponge
Classification of Phylum Porifera
The phylum is classified into three classes these are:
- Habitat: Marine, shallow coastal water
- Body: skeleton is composed of calcareous spicules made up of calcium carbonate.
- Symmetry: They show radial symmetry, with cylindrical bodies.
- The organization of the body is asconoid, syconoid, or maybe leuconoid.
- Example: Clathrina, Scypha
- Habitat: Marine
- Skeleton made by six-rayed siliceous spicules.
- Symmetry: radial with shape cylindrical
- The Canal system is found in Sycon or Leucon
- Example: Euplectella, Hyalonema
- Habitat: Freshwater or Marine
- Body: asymmetrical and cylindrical in shape
- Leuconoid-type canal system
- Skeleton consists of spongin fibers, siliceous spicules, and are monoaxon and triaxon.
- Example: Spongia, Spongilla, etc.
Some examples of porifers: Sycon (Scypha), Euspongia (Bath sponge), Hylonema, and Spongilla (Freshwater sponge)
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