Kidney Sponge

Overview

The Kidney Sponge (Chondrosia reniformis) is a distinctive, fleshy demosponge commonly found in the Mediterranean Sea and parts of the eastern Atlantic. It is easily recognized by its smooth, rubbery texture and kidney-like appearance, often forming rounded lobes on hard surfaces.

Appearance

This sponge lacks the typical siliceous spicules and spongin fibers found in many other sponges, relying instead on a dense, collagen-rich mesohyl that gives it a tough, leathery consistency. Its coloration is highly variable depending on light exposure: individuals in brighter areas tend to be brown with lighter marbling, while those in shaded or cave environments often appear milky white or purplish with white spots. They typically grow in lobes ranging from 10 to 40 cm in diameter and feature a smooth surface with a few large, visible oscules.

Distribution & habitat

Chondrosia reniformis is primarily found in the Mediterranean basin, with populations also documented in the eastern Atlantic, including the Azores and along the African coast. It favors hard substrates and is frequently encountered in shaded areas, such as under rocky overhangs, within crevices, or at the entrances of underwater caves, typically at depths down to 30–40 meters.

Biology & behavior

Unlike many other sponges, this species exhibits a notable ability to stiffen its body in response to mechanical stimulation, a process mediated by its outer epithelium. It is a filter feeder that processes surrounding water to capture microscopic planktonic prey. Due to its high collagen content, it has become a subject of interest for biotechnological and biomedical research regarding marine-derived biomaterials.