Sponges are primitive multicellular animals that lead an attached lifestyle. They are common in fresh and salty water bodies of different climatic zones, represented by both solitary and colonial forms.
The body of the sponges is porous and has a goblet shape. In the upper part of the body there is an opening – the mouth through which the cavity of the body of the sponge (paragastric cavity) communicates with the environment. The body wall consists of the outer (ectoderm) and inner (endoderm) layers, between which there is a gelatinous substance – mesoglea.
The mouth is an opening in the body of the sponges through which the body cavity communicates with the environment.
Ectoderm is the outer layer of cells.
In the ectoderm, cells of the integumentary epithelium (flat cells) are located.
The integumentary epithelium is a tissue consisting of cells tightly pressed against each other, separating the body from the environment and performing a barrier and protective function.
Endoderm is the inner layer of cells.
The endoderm consists of cells with a flagellum – choanocytes. The movement of the flagellum forces water into the body of the sponge.
Mesoglea is a gelatinous substance that sits between the outer and inner layers of the body.
In the median gelatinous substance, there are supporting cells that form the skeleton, amoebocytes that digest food and provide regeneration, as well as germ cells.
Regeneration is the restoration of lost body parts.
The skeleton of the sponges consists of needles – spicules, a substance – spongin takes part in its formation, which holds the needles together.
Spicules are needles that form the skeleton of sponges, mostly calcareous or siliceous.
Spongin is a substance that holds spicules together.
Nutrition, respiration and excretion
The sponges are nourished, breathed and excreted by the flow of water through their body. Water enters the pores and exits through the mouth. Nutrients from the water are taken up by choanocytes and transferred to amoebocytes, which digest them. Thus, according to the method of feeding, sponges are filter feeders. Thanks to this, the sponges can purify the water in the reservoir.
Sponges are capable of reproducing both sexually and asexually.
Asexual reproduction is carried out by budding, or fragmentation.
When fragmented, the body of the sponge breaks up into parts, each of which gives rise to a new organism.
During sexual reproduction, sperm from one sponge with a stream of water enters the body of another. As a result, a new organism is formed in the larval stage, which enters the environment, attaches to the substrate, and turns into an adult sponge. The larval stage is necessary for the dispersal of the sponges.
Sponges have a well-developed passive defense, such as the presence of mineral needles, the production of toxic chemicals.
The meaning of sponges
Sponges serve as food for other animals, habitat for small parasitic crustaceans. Some of them are used in medicine, perfumery, and as fertilizers.