General characteristic features of phylum Porifera

  • Poriferans (Pore bearing animals) are the first multicellular animals.
  • They are commonly called sponges because of their appearance.
  • They are aquatic, mostly marine, rarely fresh water (e.g. Spongilla).
  • They may be solitary or colonial.
  • All adults are sessile attached to the substratum but their larva is motile.
  1. Body pores:
  • Body is porous (provided with pores) i.e. ostia and
  • Ostia, also called inhalant pores or inlet canals are small and many in number distributed throughout the body surface.
  • Osculum, also called exhalent pore or outlet canal is a single large opening on the top of their bodies.
  • Body of sponge has a large spacious cavity called spongocoel or paragastric cavity which opens through osculum at the top.
  1. Body symmetry:
  • They are asymmetrical, some are radially symmetrical.
  • They have cellular level of organization and cell-aggregated body plan.
  • The whole body consists of a group of well differentiated cells.
  1. Body wall:
  • They are diploblastic. i.e. body wall with 2 layers; outer dermal layer or pinacoderm, and inner gastral layer or choanoderm.
  • Pinacoderm consists of pinacocytes and porocytes. Pinacocytes are flat and multinucleated polygonal cells.
  • Porocytes are oval and uninucleated cells with intercellular pore called prosopyle.
  • Choanoderm consitsts of only collar cells or choanocytes or flagellated cells.
  • In between outer and inner layer, there is a mesenchyme, a non-cellular layer. It contains collagen fibers, spicules and amoebocytes.
  • Almost all sponges possess an internal skeleton of tiny calcareous or siliceous spicules or of fine sponging fibers or of both.
  1. Mode of nutrition:
  • They are filter feeder and holozoic and take solid food.
  • Digestion is intracellular and takes place in food vacuole and chonaocytes.
  1. Circulation and excretion:
  • Circulation takes place by wandering of amoebocytes.
  • Excretion occurs through general body surface by diffusion and they are ammonotelic.
  1. Reproduction:
  • Asexual reproduction takes place by budding and gemmule formation.
  • They are hermaphrodite and protogynous (female reproductive organ maturing faster than male) animals.
  • Sexual reproduction occurs by the production of ova and sperm.
  • Development is indirect and larva (amphiblastula or parenchymula) is free swimming.

Classification of Porifera:

Phylum porifera is classified into three classes on the basis of skeleton or spicules they possess.

Class: Calcarea

  • They all are marine, shallow and coastal water species.
  • Body is vase shaped and comparatively simple in structure.
  • They have a radially symmetrical body.
  • Skeleton consists of calcareous spicules made up of carbonate of lime.
  • Spicules may be monoaxon, triaxon, tetraxon.
  • Canal system is Ascon or Sycon
  • e.g. Sycon, Grantia, Leucosolenia.

Class: Hexactinellida

  • They all are marine and deep sea species.
  • Body is vase shaped or cylindrical.
  • They are radially symmetrical.
  • Skeleton consists of siliceous spicules which are triaxons with six rays.
  • Canal system may be Sycon or Leucon
  • e.g. Hyalonema, Euplectella

Class: Demospongiae

  • They may be fresh water or marine.
  • Their body is massive and asymmetrical.
  • Canal system is Leucon type.
  • Skeleton consists of Spongin fibers, siliceous spicules which are monoaxon and triaxon.
  • e.g. Euspongia, Spongilla

General characteristic features of phylum Porifera