Chondrosia reniformis is a sponge of the Demospongiae class, which is classified within the Chondrosiida order and Chondrosiidae family. It lives in waters up to 30 meters deep, being mostly present in the Mediterranean Sea, although specimens have been described in the eastern Atlantic Ocean, from the Cape Verde Islands to Great Britain.
The body of Chondrosia reniformis is formed by a kidney-shaped structure that reaches between 4 and 12 cm in diameter, with a smooth surface and a firm and leathery consistency. On its external surface there are two types of orifices, several large, conical-shaped osculi (exhalant orifices) with an ascending ridge, as well as a multitude of very small inhalant orifices that are not visible to the naked eye. The color of Chondrosia reniformis is variable depending on the particularities of the place where they live. The colors range from dark brown with a light pattern in those specimens located in well-lit places, to a purplish color with white spots when they are located in rather shady places; they can even be completely whitish when they live inside caves or large crevices. As a characteristic of Chondrosia reniformis, the body of this sponge lacks spicules and spongina fibers, and only has collagen fibers that make the functions of support of the body of the specimen.
As usual in sponges, Chondrosia reniformis feeds by filtering the water column to capture the organic particles present in it. Through the multitude of small inhalant pores, the water is conducted into the body of the specimen, where specialized cells capture the particles and is used for gas exchange, oxygenating the animal and getting rid of the carbon dioxide (CO2) generated. Subsequently, the filtered water is expelled through the large openings (exhalant osculi).
Reproduction of Chondrosia reniformis can be asexually by fragmentation of a specimen, the fragments of which are dispersed in the water and subsequently each fragment becomes an individual sponge. Sexual reproduction takes place by the generation of gametes. The spermatozoa are expelled by the osculum in large quantities and can penetrate another sponge carried by the current. Once inside, they reach the eggs and fertilization occurs. The zygotes transform into ciliated larvae that are released into the water, where they can transform into adult sponges.
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