Four-lined Polycera

Overview

The Four-lined Polycera (Polycera quadrilineata) is a common and iconic nudibranch found in the North East Atlantic, ranging from Greenland to the Mediterranean Sea. Often observed in large numbers, this sea slug is frequently encountered on rocky substrates and kelp forests where it hunts for its preferred prey.

Appearance

This species typically features a translucent white body adorned with yellow or orange pigment, which often forms five longitudinal lines along the back. It possesses four—and occasionally six—pointed oral veil processes at the front of the head. The rhinophores are lamellated on their upper halves and lack basal sheaths. The branchial plume at the rear consists of up to 11 gills, flanked by two distinct, orange-tipped processes. While the base color is usually white, some individuals exhibit black spots or streaks, and in rare cases, the entire body may appear dark or black.

Feeding

This nudibranch is a specialized predator that feeds primarily on bryozoans. Its diet commonly includes Membranipora membranacea, which grows on kelp blades, as well as other bryozoan species such as Electra pilosa found on red algae.

Reproduction

During the spring, these nudibranchs become more active and are frequently seen spawning. They deposit their eggs in the form of a short, curved, white ribbon, often attaching them to the blades of seagrass or other marine vegetation.