Sertularelle Polyzonias

Overview

Sertularella polyzonias is a colonial hydroid characterized by its thin, wavy, and pale straw-colored stems. It is widely distributed across the Atlantic Ocean and the Mediterranean Sea, where it is often found in areas with significant water movement.

Appearance

These hydroids typically form colonies reaching 40–50 mm in height, featuring a loose and irregular branching pattern. The side branches support alternate hydrothecae—small, bulbous structures that narrow toward the rim. Each rim is equipped with four cusps and an operculum consisting of four triangular flaps. The reproductive structures, or gonothecae, are generally ovate and slightly rugose in texture, with a raised tubular aperture. Sexual dimorphism is present: male gonothecae are white and smaller, while female gonothecae are yellow.

Distribution & habitat

This species is common throughout the British Isles and is reported widely across the Atlantic and Mediterranean. It is typically found in shallow sublittoral zones but can occur at considerable depths. It often grows attached to hard substrates such as shells, algae, polychaete tubes, or other hydroids, favoring environments with active water flow.