Question

Give the main features of the phylum Porifera.

Answer 1

Kingdom: Animalia

Habitat: Aquatic, mostly marine, few are terrestrial

Habit: They are solitary or colonial.

Grade of organization: cellular grade of body

Shape: Body shape is variable, mostly cylinder shaped

Symmetry: Asymmetrical or radially symmetrical.

Germ layer: Diploblastic animals. The adult body wall contains two layers, outer dermal layer and inner gastral layer. In between these two layers, there is a gelatinous and non-cellular mesoglea containing numerous free amoeboid cells.

Coelom: Absent; acoelomate but spongocoel is present

Surface of the body has numerous perforation called ostia (for the entry of water) and a large pore at the apex called osculum (for the exit of water).

Water canal system present

Endoskeleton: Either calcareous spicules (calcium carbonate) or siliceous spicules (silica) or sponging fibers (protein).

Nutrition: holozoic

Digestion: Intracellular

Nervous system: absent

Circulatory system: absent

Reproduction:

Asexual: by budding or gemmule or regeneration

Sexual: gamatic fusion

Fertilization: Internal

Answer 2

Poriferans are commonly called sponges.
These are multicellular organisms which are sessile/sedentary in nature.
Most of them are marine while a few are fresh water forms.
Body is cylindrical, asymmetrical or has radial symmetry.
Body wall is diploblastic which consists of an outer layer called pinacoderm and an inner layer called choanoderm.
The middle layer is called mesenchyme which has various kinds of wandering amoebocytes.
Body wall contains numerous pores called ostia through which water enters in the body through a canal system into the central body cavity, called spongocoel.
The canal syytem mainky comprise of incurrent and excurrent canals which are lined with pinacocytes; and radial canals which are lined with choanocytes (flagellated cells).
Body also contains one or more openings called oscula (-um/singular) through which water passes out from the body.
Sponges feed on minute organisms and small organic particles which enter the body through water current and are ingested by the choanocytes.
Respiration takes place by diffusion of oxygen from water the flowing into the body.
Sponges have an exoskeleton which is made up of either spongin fibers or calcareous/siliceous spicules or a combination of both.
Excretory product, mainly ammonia, is released from the body through outgoing water current.
Reproduction may be asexual or sexual.
Asexual reproduction takes place by external or internal budding (formation of gemmules) or by disintegration of body into reduction bodies.