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Sponges have bodies in the form of tubular vases or globes open in the upper extremity. They have an internal central cavity and porous walls. The central cavity is called spongocoel and the opening in the upper extremity is called osculum.

Sponges live exclusively in an aquatic environment and they are attached by their base to a substrate (fixation ground). Sponges are filtering animals, they nourish themselves from nutrients that enter their atrium brought in with water.

The phylum Porifera contains the simplest creatures of the animal kingdom. Sponges are aquatic sessile beings (they are not able to move by themselves and they keep themselves attached to substrates), they do not have tissue diversity and their bodies have pores (feature after which their name comes).

They are multicellular, like all beings of the animal kingdom.

Sponges have their outer wall covered by flat cells called pinacocytes and having pores well-delimited by special cells called porocytes. The internal wall is filled with choanocytes, flagellate cells specialized in phagocytosis of food brought to the central cavity; the choanocyte flagella also maintains the water flux inside the sponge.

Between the outer and the inner coverage of the poriferan body there are cells with amoeboid movement (by pseudopods), the amoebocytes; since they are embedded in connective matrix, amoebocytes move and distribute nutrients to other cells and they also produce spicules that like a primitive skeleton fill the tissue and support the body structure. (Some poriferans have an internal skeleton, an endoskeleton, made of spicules and organic fibers.)

Sponges can close their pores to avoid the entrance of water into their bodies in the presence of stimulus that may mean danger. This method however is rudimentary but it is actually a protection attempt against nocent agents. 

Sponges are filtering beings. They make water enter their bodies by their lateral pores. Water then circulates inside the central cavity and exits through the osculum.

Apart from sponges, that do not have a digestive cavity where extracellular digestion takes place, all other animals have a digestive system with an internal cavity in which extracellular digestion occurs.

The sexual reproduction in sponges, in addition to contributing to genetic variability, also facilitates the colonization of farther environments by these beings, since sperm cells and larvae are mobile and can swim in the exterior to compensate the immobility of the adult individual.