Phallusia nigra is a species of sea squirt (tunicate) found in tropical seas around the world. It is usually found in shallow waters attached to any hard substrate. It is a solitary animal rather than living in colonies. Although the native range of this animal is unknown, the tropical western Atlantic Ocean, the Red Sea and the Indian Ocean are possibilities.
Like all ascidians, this species has a thick leathery envelope (tunic) containing cellulosic material. The tunic encloses a sac-shaped body with separate water entrance and exit siphons. The adult is about 4 inches in length. The tunic is typically velvet black or dark brown, but may be gray in some specimens that are younger or live in shaded areas. The tunic also contains many vesicles filled with a strong acid (pH near 1). The vesicles are concentrated towards the outer surface and are easily ruptured by contact; they are believed to protect the animal from predators and other stresses.
Substances extracted from the dried tunic have been found to have cytotoxicity, antibacterial, antipyretic, analgesic and histamine-like properties.
Image Caption: Specimen of the ascidian Phallusia nigra collected near the USP station in São Sebastião, São Paulo state, Brazil. Credit: Jorge Stolfi/Wikipedia(CC BY-SA 3.0)