Phylum Porifera-General Characters

Phylum – Porifera
The animal nature of sponges was established by Ellis
Name porifera was coined by Robert Grant
Study of sponges is called parazoology
• Phylum Porifera: sponges are sessile with porous bodies and choanocytes
• The sponges, in the phylum Porifera, are the only members of the subkingdom Parazoa
• due to their unique development and simple anatomy (see Campbell, Figure 33.1).
• Approximately 9000 species, mostly marine with only about 100 in fresh water
• Lack true tissues and organs, and contain only two layers of loosely associatedunspecialized cells
• No nerves or muscles, but individual cells detect and react to environmentalchanges
• Size ranges from 1 cm to 2 m
• All are suspension-feeders (= filter-feeders)
• Possibly evolved from colonial choanoflagellates
• Parts of the sponge include (see Campbell, Figure 33.2):
• Spongocoel = Central cavity of sponge
• Osculum = Larger excurrent opening of the spongocoel
• Epidermis = Single layer of flattened cells which forms outer surface of thesponge
• Porocyte = Cells which form pores; possess a hollow channel through the centerwhich extends from
the outer surface (incurrent pore) to spongocoel
• Choanocyte = Collar cell, majority of cells which line the spongocoel; possess a flagellum which is
ringed by a collar of fingerlike projections. Flagellarmovement moves water and food particles which are
trapped on the collar andlater phagocytized.
• Mesohyl = The gelatinous layer located between the two layers of the spongebody wall (epidermis
and choanocytes)• Amoebocyte = Wandering, pseudopod bearing cells in the mesohyl; function infood
uptake from choanocytes, food digestion, nutrient distribution to othercells, formation of skeletal fibers,
gamete formation
• Spicule = Sharp, calcium carbonate or silica structures in the mesohyl whichform the skeletal fibers
of manysponges Spongin = Flexible, proteinaceous skeletal fibers in the mesohyl of somesponges
• Most sponges are hermaphrodites, but usually cross-fertilize.
• Eggs and sperm form in the mesohyl from differentiated amoebocytes or choanocytes.
• Eggs remain in the mesohyl.
• Sperm are released into excurrent flow of the spongocoel and are then drawn in with incurrent flow
of anothersponge.
• Sperm penetrate into mesohyl and fertilize the eggs.
• The zygote develops into a flagellated larva which is released into the spongocoel and escapes with
the excurrent water through the osculum.
• Surviving larvae settle on the substratum and develop. In most cases the larva turns inside-out
during metamorphosis, moving the flagellated cells to the inside. Sponges possess extensive regeneration
abilities for repair and asexual reproduction
• Members of this phylum are commonly known as sponges.
• They are generally marine and mostly asymmetrical animals.
• These are primitive multicellular animals and have cellular level of organisation.
• Water Transport System in Sponges: Sponges have a water transport or canal system. Water enters
through minute pores (ostia) in the body wall into a central cavity, spongocoel, from where it goes out
through the osculum. This pathway of water transport is helpful in food gathering, respiratory exchange
and removal of waste. Choanocytes or collar cells line the spongocoel and the canals.
• Digestion is intracellular.
• The body is supported by a skeleton made up of spicules or sponging fibres.
• Reproduction: Sponges are hermaphrodite animals. Sexes are not separate, i.e., eggs and sperms
are produced by the same individual.
• Sponges reproduce asexually by fragmentation and sexually by formation of gametes.
• Fertilisation is internal and development is indirect having a larval stage which is morphologically
distinct from the adult.Larva is amphiblastula and parenchymula.
Examples:
Spongilla:Fresh water sponge
Euspongia:bath sponge
Euplectella:Venus flower
basket
Pheronema:Bowel sponge
Hyolema:glass rope sponge
Cliona:Boring sponge
Chalina:dead mans
finger,Mermaids gloves
Sycon:Scypha
Phyllospongia:Leaf sponge