Updated by: Arabinda Naik
Phylum—Porifera (Porous — pore; ferre — to bear) includes the first and the most primitive group of multicellular animals, referred to as poriferans, i.e., pore bearing animals. They are primitive, multicellular animals and are commonly called sponges.
General Features
Habitat: They are mostly marine, and some are freshwater habitat, found in ponds and lakes, e.g., Spongilla.
Shape and Size: The size of sponge’s ranges from 1 cm 1 m in length. Some of them have vase like cylindrical shape and majority have irregular shape.
Symmetry: The cylindrical form (e.g., Sycon) show radial symmetry while, sponges showing irregular shape and have no symmetry.
Body Wall :The body wall contains outer dermal layer or pinacoderm and inner gastral layer or choanoderm. The pinacoderm contains flat cells called pinacocytes. The choanoderm consists of spherical cells with collar from which a flagellum emerges out. Hence, they are also called flagellated cells or collar cells.
Body Organisation: Sponges show cellular level of organisation. The cells are almost independent, i.e., cooperating very little with one another in function.
Germ Layers: These are diploblastic.
Body cavity: The sponges have a large cavity ca e spongocoel or paragastric cavity. It opens to the outside by terminal opening called osculum.
Skeleton: It is internal and includes inorganic spicules and organic spongin fibres. Canal System It is one of the most important features of sponges. Canal system is the network of channels called canals, which connect the spongocoel to the outside through ostia. The canals arc lined by choanocytes. It maintains a constant flow of water from ostia to osculum through spongocoel. It helps in nutrition, respiration, reproduction, and excretion.
Digestion Digestion: in animals of this phylum is intracellular (inside collar cells) in nature.
Circulation: The amoeboid cells transport food from ingesting cells to other cells. Respiration It occurs through the surface by diffusion.
Excretion: It also occurs through the body surface by diffusion in the form of ammonia.
Sensory System: Sponges lack sensory and nerve cells, so they are poor in response to stimuli.
Reproduction: Sponges reproduce both sexually and sexually. Asexual reproduction Occurs by budding or gemmules or internal buds. Sexual reproduction involves the fusion of ova and spermatozoa.
Fertilisation and Development: Fertilisation is Interna i.e., sperms of one sponge are carried by Water current to the ova of another sponge for fertilisation. Development is mostly indirect with larval stages called parenchymula (Leucosolenia) or amphiblastula (Sycon).