Aplysia fasciata, commonly known as the black sea hare, is a species of sea slug belonging to the family Aplysiidae. These gastropod mollusks are found in the coastal waters of the Mediterranean Sea, including the Comunidad Valenciana.

This species is notable for its distinctive body features:

• Appearance: Aplysia fasciata can be identified by its large, soft body and its characteristic dark coloration, which can range from deep brown to black. It often has a slimy texture.
• Size: This mollusk can grow quite large for a sea slug, with some individuals reaching lengths of up to 40 cm.
• Defense Mechanism: When threatened, Aplysia fasciata can release a purple ink-like substance as a deterrence against predators.
• Diet: They are herbivorous, feeding primarily on algae, which contributes to their coloration.

The Aplysia fasciata plays an essential role in its ecosystem, often serving as a food source for various marine animals. Additionally, its presence is important for studying neurological functions due to its simple nervous system, making it a significant species in scientific research.