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The Sponges Phylum Porifera
Commonly known as sponges. • ~ 9,000 species • They are pore-bearing multi-cellular animals. • lack germ layer. • No internal organs. • No muscles. • Sessile, fixed, immobile. • Asymmetric.
Three types of cells involved in sponge formation • Pinacocytes. • Choanocytes. • Mesenchyme. • Pinacocytes: • Will form pinacoderm. • Some specialized as porocytes, and regulate water circulation.
Choanocytes: • Will form inner layer choanoderm. • They are flagellated collar cells. • Flagellum and collar together, are used to gather food.
Mesenchyme cells: • These cells specialized to perform function in: • Reporoduction. • Transport. • Storing food.
Sponge Structure • Simple in structure. • One end attach to solid substratum. • Other end has opening, Osculum. • Ostia present over the body surface. • Outer layer is pinacoderm. • Inner layer is choanoderm. • Between them is mesohyl. • Large internal cavity is spongocoel.
Sponges have skeleton. Two main component of skeleton: • Spongin: a proteinecious fibrous network. • Spicules: Needle-like spikes of silicon or cacium carbonate. • Provide support to sponge
Water Canal System Essential element of water current system are: • Choanocytes/collar cells: • Generate water current. • Capture food particals and carry oxygen. • Osculum: • An opening through which water is expelled.
Three types of sponge body form are described based on the arrangement of water-current system: • Ascon. • Sycon. • Leucon.
Ascon Ascon sponges have very simple canal system. • Vase-like shape. • Water enter through ostia • Lead to large internal cavity spongocoel. • Expelled through osculum.
Sycon • Osculum and spongocoel present. • Body wall invaginations are incurrent canal. • Incurrent canals have dermal pores. • Pores connect incurrent canal to radial canal. • Water enter through pores of incurrent and radial canal into the spongocoel and expelled through osculum.
Leucon • Complex water current system. • Have extensively branched canal system. • Incurrent canal branching will form choanocytes chamber. • Canal carrying water away from chambers are excurrent canals. • Spongocoel absent. • Multiple osculum.
Feeding • Sponges consume bacteria or small prey. • Choanosytes sweep and filter suspended food particles. • Digestion begins in food vacuole. • Partially digested food pass to mesohyl for distribution. • Pinacocytes phagocytize large food particle. • Gas exchange and nitrogenous waste remove by diffusion.
Reproduction Reproduce by sexual and asexual manner. Sexual Reproduction: • Hermaphrodite animals. • Protogynous/Protandrous • Avoid self-fertilization. • Choanocytes will form sperms and eggs. • Sperm released through osculum.
Sperm from one sponge enter the body of another sperm and trapped by choanocytes. • After fertilization zygote will form. • Early development lead to formation of flagellated larva. • Larva moves out from parent sponge. • Attach to substratum and develop into new adult.
Asexual Reproduction: • Sponges reproduced asexually by gemmulation. • Mesenchyme cells enclosed themselves in protective capsule to overcome adverse condition. • Capsule expelled from parent sponge. • Under favorable conditions, cells comes out from capsule by micropyle. • Organize themselves into new sponge.
Classification • Class Calcarea: • Calcareous sponges. • Spicules made of calcium carbonate. • They are tubular. • Body form may be ascon, sycon or leucon.
Class Hexactinellida: • Commonly known as glass sponges. • Spicules bound in glass-like lattice. • They are siliceous. • Body form may be sycon or leucon. • Class Demospongia: • They have spicules and spongin. • Spicules are siliceous. • Body form is leucon.
