White Sea-squirt

Overview

The White Sea-squirt (Phallusia mammillata) is a solitary marine tunicate frequently found along European coasts, including the Mediterranean Sea and the northeastern Atlantic. As a filter-feeding invertebrate, it plays a role in its ecosystem by processing planktonic particles from the water column through a specialized mucous net.

Appearance

This species is characterized by a thick, leathery, and translucent tunic that often displays a bluish-white hue. Its body is typically conical or sac-shaped, featuring a broad base and a surface covered in irregular, rounded lobes or mounds. Individuals can reach a height of approximately 20 cm.

Biology & behavior

Phallusia mammillata is notable for its unique ability to accumulate high concentrations of the element vanadium in its blood cells, reaching levels millions of times higher than those found in the surrounding seawater. The animal possesses two distinct siphons—one for drawing in water and another for expelling it—which are essential for its filter-feeding process.

Reproduction

This species is a simultaneous hermaphrodite, meaning each individual possesses both male and female reproductive organs. Reproduction involves the release of eggs through the exhalent siphon, followed by external fertilization within the water column. The resulting embryos develop into swimming larvae, a process that is highly valued in scientific research due to the transparency of the eggs and embryos.