Black Flatworm

Appearance

This flatworm body is leaf-shaped, very flattened, with lobed and wavy edges. P. splendidus is a large planarian: 50 mm in length (60 mm maximum). It has a velvety appearance and its color varies from black to dark blue-black in our Mediterranean waters, while the dominant color is more or less dark brown in the Atlantic specimens. In all cases the edges are marked with a yellow-orange border, separated by a fine dark line at the junction of the dorsal and ventral side (extreme edge of the body). The hidden (ventral) side of the body is lighter in color, often blue-grey.
The presence of a central-ventral suction cup allows it to attach itself on the bottom if necessary (to avoid being swept by the current etc.). This cup is placed right next to the female genital opening.
Formed by the folding of the front edge of this flatworm, two relatively well-defined tentacles are clearly visible. They are widened at their base and pointed at their tip. Arranged in a horseshoe shape between the tentacles, a series of ocelli allow the animal to orient itself in relation to the light, as these are visual organs.
The ventral part of the body is dotted with small cilia that create movement in the water, allowing the worm to move. Locomotion is favored by a muscular band under the epidermic layer, which by contracting causes the lifting and lowering of the ventral surface, which makes the worm undulate. The planarian can also swim in open water.
A dorsal thickening is well marked along the entire length of the body, which gives a little volume to its body.

Naming

Plathelminthes: from [platea] = broad and flat, and [helminthes] = worms.
Turbellariés: [turbella] in Latin means agitation. These are animals that move by “agitation” of vibrating cilia.
Pseudobiceros: from Latin [Pseudo] = false, and [biceros] = two horns. it comes from the fact that it looks like it has 2 horns, whereas this is the shape of its "head".
splendidus: directly from Latin = brilliant, dazzling, resplendent (Gaffiot) therefore splendid.

Distribution

Initially described as endemic to the Mediterranean, this little-studied black flatworm seems to have a much wider distribution, it has been described from the Atlantic (Africa) to Australia and Papua New Guinea, the Caribbean etc.

Behavior

Attracted to intense light.

Habitat

Rocky bottoms rich in calcareous algae, crevices, interstices of rocks, depth from 5 to 50 m. Like all planarians, it has difficulty moving on soft bottoms. Although mostly on the bottom, this black planarian can swim through synchronous full-body ripples.

Reproduction

The black flatworm is hermaphrodite: like all planarians, fertilization is crossed between two individuals. The fertilized eggs are deposited on the bottom in a gelatinous cocoon. This planarian has a male copulatory organ and a female genital orifice which extends into a branched uterus.
On the other hand, planarians have a great capacity for regeneration, so an animal can reconstitute itself from just a small torn piece of this flatworm.

Food

It is a carnivorous predator of ascidians, bryozoans and other small animals, which it captures by wrapping them and secreting a viscous mucus. Like all turbellarians, the digestive tract has only one opening, the mouth, and no anus. Ingested food and undigested food need to be eliminated through this same opening.