Sertularelle De Méditerranée

Overview

Sertularella mediterranea is a small colonial hydroid typically reaching heights of around 2 cm. It is anchored to its substrate by a network of root-like tubes known as stolons, from which its generally simple, occasionally branched stems arise.

Appearance

The colony consists of erect, monosiphonic stems divided into segments called internodes, which are arranged in a characteristic zigzag pattern. Each internode supports a single, flask-shaped hydrotheca—a small protective capsule that houses the feeding polyp. These hydrothecae are swollen at the base and feature a rim with four distinct cusps. Fertile colonies can be identified by the presence of elongated, ovoid reproductive structures called gonothecae, which exhibit 6 to 9 transverse ridges and are topped with four or five pointed cusps.

Biology & behavior

This species is a microphage, meaning it captures small organisms from the surrounding water column using its tentacles. In the Mediterranean, fertile specimens can be observed throughout the year. It is sometimes confused with young, unbranched colonies of the related species Sertularella polyzonias, though the latter typically exhibits more frequent and irregular branching as it matures.