Cereus pedunculatus

Cereus pedunculatus is a solitary anemone belonging to the family Sagartiidae (phylum Cnidaria, order Actinaria). It inhabits waters up to 30 meters deep in the Mediterranean Sea, as well as in the Atlantic Ocean, from the eastern coasts of the British Isles to the western coasts of Africa. This species is usually found in rocky bottom crevices, where sediment accumulates on which these anemones grow.

The disc of the body of Cereus pedunculatus is flattened and has a diameter of up to 7 cm. Surrounding the disc we find a multitude of short tentacles (no longer than 2 cm) and conical in shape, arranged in 8 or more rows. Each specimen may have more than 768 tentacles. On the underside of the disc, we find a caudal peduncle that is up to 4 cm in diameter and 10 cm long, which is buried in the substrate. Although the caudal peduncle is rarely visible, it is of a striking orange or grayish color.

As for the coloration of Cereus pedunculatus, this can be varied, and will be determined largely by the presence of zooxanthellae algae inside their tissues. We can find specimens with white, yellow, reddish, greenish-brown, or grayish tones. In poorly lit areas, the specimens tend to have whitish colors, since the absence of light means that the tissues of the specimens have very few zooxanthellae.

The feeding of these anemones is obtained in two ways. On the one hand, their tentacles have stinging cells capable of capturing small prey from the zooplankton. These prey will be directed towards the mouth opening of the body disc of the specimen, where they will be digested and assimilated. The second way of obtaining energy is from zooxanthellae algae. This is a symbiotic relationship, in which both organisms benefit. Cereus pedunculatus obtains the products generated by photosynthesis carried out by the zooxanthellae, while the algae have a very protected environment and direct access to sunlight.

There are both dioecious individuals, that is to say male specimens differentiated from female specimens, although hermaphrodite specimens can also be found. The reproduction of Cereus pedunculatus is sexual and usually occurs during the spring and summer months.

Among its predators we find the nudibranch Aeolidiella alderi, which not only feeds on the tissue of Cereus pedunculatus, but also that of other actinarians.