Wandering Cratena

Overview

The Wandering Cratena (Cratena peregrina) is a striking and widely recognized nudibranch commonly found in the Mediterranean Sea and parts of the eastern Atlantic. This slender sea slug is easily identified by its vibrant, multi-colored cerata and distinct orange markings on its head.

Appearance

This species features a translucent, milky-white body with a long, pointed tail. Its back is covered in 8 to 10 symmetrical clusters of elongated, finger-like appendages called cerata. These structures vary in color—ranging from orange and red to purple or brown—depending on the animal's diet, as they contain extensions of the digestive gland. Each ceraton is tipped with a whitish or bluish cnidosac. The head bears a pair of smooth, elongated rhinophores with orange tips, long oral tentacles, and two characteristic orange spots located between the rhinophores and tentacles.

Biology & behavior

Cratena peregrina is a hermaphrodite that typically lays its eggs in spiral-shaped, whitish or pale pink ribbons near its feeding grounds. To defend against predators, it employs a specialized strategy: it sequesters stinging cells (nematocysts) from its hydroid prey and stores them in the cnidosacs at the tips of its cerata, effectively turning its own body into a deterrent.

Feeding

This nudibranch primarily feeds on hydroids of the genus Eudendrium. It practices a unique feeding behavior known as "kleptopredation," where it selectively targets hydroid polyps that have recently captured zooplankton. By consuming both the hydroid and its recently caught prey, the nudibranch gains extra nutrients, a strategy that helps it thrive on ephemeral food sources.