Eyespot Costasiella

Costasiella ocellifera

Costasiella ocellifera is a small sea slug measuring between 5 to 13 mm in length. Its body is white and somewhat translucent, speckled with small black dots. The upper surface is adorned with pointed cerata arranged in diagonal rows, which contain chloroplasts from the algae it consumes, giving them a greenish hue. A distinctive feature is the blue eyespot located behind its black eyes, which are set between two large, horn-like rhinophores. This species inhabits shallow coastal waters in the tropical and subtropical regions of the Atlantic Ocean, including locations such as the Bahamas, Belize, and Florida, typically found at depths ranging from 2 to 10 meters, often on the algae Avrainvillea nigricans. Costasiella ocellifera is strictly herbivorous, feeding primarily on Avrainvillea. It employs its radula to pierce the algal cell walls and extract the contents, including chloroplasts, which it can incorporate into its own cells for photosynthesis. This process, known as kleptoplasty, allows the slug to survive on photosynthesis alone for up to 65 days when food is scarce. The species exhibits simultaneous hermaphroditism, reproducing through internal fertilization and laying eggs in a spiral pattern on the algae. Encounters with this sea slug during dives can be intriguing, as divers may observe its unique coloration and the way it blends into its algal habitat. Although it has developed chemical defenses from the algae it consumes, divers should approach with care to avoid disturbing its environment. The conservation status of Costasiella ocellifera is not evaluated.