Decompression is a boring phase of diving but from a certain point of view it can also be interesting if, in addition to looking at the computer, which marks the times and stages of depth, we take a look around in the deep blue.
Often it happens to meet fish that intrigued approach the diver, sometimes it has also happened to meet dolphins that intrigued by the bubbles have approached to be filmed for a moment and other times, as in this case, it happens to meet some vagabonds of the sea like ctenophores and jellyfish that, letting themselves be carried away by the current, involuntarily “come within range of the camera”.
In this collage of videos made in two different dives a few days apart but always in the same stretch of sea we filmed one of the many species of ctenophores that inhabit our Mediterranean Sea, from some research it seems to be the Bolinopsis infundibulum or tentacled Ctenophore.
Bolinopsis infundibulum is a species of tentacled ctenophore, first described in 1776 by the naturalist Otto Friedrich Müller.
Bolinopsis infundibulum is an oval ctenophore, up to about 15 cm long, with an almost transparent or whitish appearance. It has two small tentacles. The mouth is located at one end of the body, where there are two large lobes useful for catching food. Here are four auricles that produce currents that allow the animal to capture prey.
The 8 bioluminescent rows of ctenes allow the animal to move easily along the water column, even if the animal is planktonic. The cats move synchronously, which also gives the animal an iridescent appearance.
The range of Bolinopsis infundibulum is very vast: it goes from the North Atlantic to the North Sea, also passing through the Mediterranean Sea. It can be observed at considerable depths (1000 m), but usually younger individuals are found at shallower depths.
Its resemblance to the more famous sea nut is remarkable: a characteristic that has made the recognition of the two species cryptic in the North Sea. The first sightings of Mnemiopsis leidyi in that area date back to 2005, but it cannot be excluded that it arrived well before and that it was confused with B. infundibulum.
The preys of B. infundibulum are all weak swimmers who can become victims of the currents generated by the animal’s tentillae: fish eggs and fry, copepod larvae, gastropod veligers, rotifers and other zooplankton.
Bolinopsis infundibulum is in turn prey to another ctenophore: Beroe cucumis. In May, up to 250 individuals per square meter were recorded in Norwegian waters, followed by a rapid decline caused by this other ctenophore. Larger individuals of B. infundibulum have been reported from deeper waters, preying on copepods, later in the year.