Holothuria poli is a species belonging to the Holothuridae family, which in turn is included in the Holothuriida order and is in the Holothuroidea class. It is a species found in the waters of the Mediterranean Sea, Red Sea, and in the Atlantic Ocean from the Canary Islands to the Bay of Biscay. The preferred habitat of this species are the bottoms of up to 20-40 meters deep, with sandy substrates, rocky, algae meadows (especially Caulerpa and Posidonia oceanica where they are very frequent).
The body of Holothuria poli is cylindrical and elongated, and can reach up to 25 cm maximum total length and 5 cm in diameter. The anterior end of the body has tentacles that surround the mouth and are fully retractable. At the opposite end is the anal opening. The skin is thick and leathery, with small calcareous spicules embedded inside. The skin is notable for the presence of numerous conical papillae of variable sizes on the dorsal part of the body.
As for the coloration of Holothuria poli, this is very variable. Specimens with grayish-brown coloration predominate on both the dorsal and ventral surfaces, with the apices of the conical papillae frequently ending in a whitish color. However, their body coloration often goes completely unnoticed since specimens tend to cover themselves with sand, bits of algae, bivalve shells and any other debris that allows them to camouflage in the environment.
Holothuria poli is a limnivorous feeding species, that is that using the tentacles surrounding the mouth, they collect sediment and filter organic particles from it. The organic particles are digested, while the sand particles and other non-digestible materials are mixed with a mucous secretion, to expel them forming sand cords.
Dioecious species, so there are Holothuria poli specimens of both sexes, although there is no differentiation to distinguish them (no sexual dimorphism). The breeding season usually occurs between the months of November to January, at which time the specimens, adopting an ‘L’ shape, rise from the bottom to release their gametes into the water column. After an external fertilization, the larvae are formed, which will pass through a planktonic phase and after several stages, descend to the bottom of the sea and undergo a metamorphosis that turns them into juvenile specimens.
Holothuria poli is often confused with other species such as Holothuria forskali and especially with Holothuria tubulosa. In the case of Holothuria tubulosa, it is never covered with sand stuck to the skin, which is how we normally find Holothuria poli.
It should also be noted that Holothuria poli lacks Cuvier’s glands, structures characteristic of certain holothurids that are used as a form of defense and through which they release whitish and very sticky filaments to disconcert possible predators before their attacks.
Photos:
from