Ver Plat Noir

Overview

Pseudobiceros splendidus is a striking marine flatworm known for its velvety, dark-colored body and vibrant marginal bands. Often mistaken for a nudibranch due to its flamboyant appearance, this species is a member of the phylum Platyhelminthes and is recognized for its ability to swim through the water column using rhythmic, synchronized undulations of its body margins.

Distribution & habitat

This species has a broad, potentially cosmopolitan distribution, with records spanning the Mediterranean, the Atlantic, the Indian Ocean, and the tropical Pacific. It is typically found in rocky or coral reef environments, often residing in crevices, under boulders, or associated with colonial ascidians and sponges.

Appearance

This flatworm features a leaf-shaped, highly flattened body that can reach lengths of up to 6 cm. Its dorsal coloration ranges from deep black or blue-black in Mediterranean specimens to various shades of brown in Atlantic populations. A defining characteristic is the bright yellow-orange border along its ruffled edges, which is often separated from the main body by a thin, dark line. The anterior end features two distinct, well-developed pseudotentacles formed by folds of the body margin.

Biology & behavior

As a simultaneous hermaphrodite, Pseudobiceros splendidus possesses both male and female reproductive organs. Like other members of its genus, it is known to engage in a complex mating behavior often referred to as "penis fencing," where individuals use their copulatory organs to attempt to inseminate one another. While it spends much of its time attached to the substrate, it can actively swim when disturbed or to navigate its environment.