12/03/2021
Animal Kingdom
Phylum Porifera
➢ Porifera means pore bearers.
➢ Members of this phylum are commonly known as sponges.
➢ Body is perforated with many pores called ostia.
➢ Ostia are mouthlets and allow entry of water.
➢ A larger aperture called osculum allows exit of water.Phylum Porifera
Habit and Habitat
➢ These are generally marine and mostly asymmetrical animals.
➢ Some sponges are found in fresh water also like Spongilla.
➢ Adult sponges are sessile or sedentary but their larvae are motile.
➢ Study of sponges is Parazoology.Phylum Porifera
Habit and Habitat
➢ These are primitive multicellular animals and have cellular level of organisation.
➢ Sponges are on a blind branch of evolutionary tree.
➢ Sponges have evolved from colonial choanoflagellates.
➢ Connecting link between Protozoa and Porifera is Proterospongia.Phylum Porifera
Body Structure
➢ Body wall has two layers i.e.
○ Outer Pinacoderm
○ Inner Choanoderm
➢ In between these two layers, a non-cellular jelly-like layer called mesenchyme is
present.
➢ Body cavity is called spongocoel or paragastric cavity or atrium.Phylum Porifera
MesenchymePhylum Porifera
Body Structure
➢ Pinacoderm has pinacocytes.
➢ Choanoderm has choanocytes.
➢ Choanocytes are also called collared
flagellated cells.
➢ These line the spongocoel and the canals.Phylum Porifera
Gas Exchange
➢ All body systems are absent.
➢ Gas exchange occurs through general body surface.
➢ There are no specialised respiratory structures.Phylum Porifera
Excretory System
➢ Excretion occurs through general body surface.
➢ Specialised excretory structures are absent.
➢ Excretory product is ammonia(Ammonotelic).Phylum Porifera
Food and Feeding
➢ These are microphagous animals.
➢ These feed on microscopic food particles like bacteria, protozoans etc.
➢ Digestion is intracellular.
➢ Food is captured by flagella of choanocytes which digest it partially.
➢ Partially digested food is passed on to trophocytes which digest it completely and
distribute it.Phylum Porifera
Skeletal System
➢ The body is supported by a skeleton made up of spicules or spongin fibres.
➢ Spicules are small needle like structures which are of two types.
○ Calcareous Spicules (made up of CaCO3)
○ Siliceous Spicules (made up of silica)Phylum Porifera
Nervous System
➢ There are no neurons but these are sensitive to external environment.
➢ Pinacocytes are contractile cells.
➢ These can increase or decrease overall surface area of sponge body.Phylum Porifera
Canal System
➢ Sponges have a water transport or canal system.
➢ It is also called aquiferous system.
➢ It is lifeline of sponges.
➢ Water enters through minute pores (ostia) in the body wall into a central cavity,
spongocoel(Paragastric cavity) from where it goes out through the osculum.Phylum Porifera
Canal System
➢ It is a system of pores, chambers and canals through which water circulates.
➢ This pathway of water transport is helpful in
○ food gathering
○ respiratory exchange
○ removal of wastes
○ reproduction.Phylum Porifera
Reproductive System
➢ Sexes are not separate.
➢ These are hermaphrodite animals, i.e., eggs and s***ms are produced by the same
individual.Phylum Porifera
Reproductive System
➢ Reproduction is asexual as well as sexual.
➢ Asexual reproduction is by
○ Fragmentation,
○ Budding
○ Branching
○ Gemmule formation.
➢ Sexual reproduction is by formation of gametes.Phylum Porifera
Fertilisation and Development
➢ Fertilisation is internal.
➢ Scypha sponge is protogynous i.e. ova matures earlier than s***matozoa.
➢ Flagella of choanocytes captures s***m and passes it to ova developing in
mesenchyme.Phylum Porifera
Fertilisation and Development
➢ Development is indirect having a larval stage, which is morphologically distinct
from the adult.
➢ Larvae are ciliated and free swimming.
➢ Larval stages are
○ amphiblastula
○ parenchymula
○ rhagon.Phylum Porifera
Examples
➢ Spongilla (freshwater sponge)
➢ Euspongia (common bath sponge)
➢ Sycon (crown sponge or urn sponge)Phylum Porifera Examples
➢ Hyalonema (glass rope sponge)
➢ Euplectella - Venus’s flower basket (It is given as a wedding gift in Japan).