Its bright orange color stands out unmistakably on the walls of submerged caves or on rocks populated by corals, gorgonians and other animals characteristic of the coralligenous. What creates that extraordinary special effect in the depths of the Mediterranean and in some areas of the eastern Atlantic is not the single specimen of Parazoanthus axinellae, commonly known as yellow cluster anemone, given its tiny size, but the extension of the colonies, which group together thousands and thousands of polyps, fixed to the substrate with a soft and unique stolon.

They are really small, the polyps, just five millimeters in diameter and about twenty in height. Each polyp has a basal part and an erect part that is retractable. The entire body is equipped with stinging cells (cnidocysts) that place the anemone among the Cnidaria or also Coelenterates, because they have a gastric cavity called coelenteron. Belonging to the class of Anthozoa, being a polyp, the anemone is a hexacoral, because it has smooth, threadlike tentacles in number between 24 and 36, therefore multiples of six, arranged in two rows around the mouth and equipped, more than the other parts of the body, with stinging cells. Thanks to the tentacles, the polyps capture the microplankton on which the animal feeds. And precisely to have food available, the species settles in places where the movement of the currents is strong. Another requirement is low light, not by chance Parazoanthus is present in marine cavities or in any case on rocky walls in the shade. The depth varies from 5 to 50 meters mostly, but colonies are found up to 200 meters. Where it encounters favorable conditions, the species expands like a carpet even on very large surfaces. The colonies can merge or split.

The groups include male and female specimens, which reproduce in spring, with the laying of eggs in March. At the end of autumn, planktonic larvae are released from the eggs and are transported by the current to create new colonies.

If they prefer hard and rocky substrate, yellow cluster anemone can also settle on other animals. And their scientific name already reveals a symbiosis with some sponges of the Axinellidae family – Axinella darmicornis and Axinella verrucosa – which are also filter-feeding animals and have the same yellow color. In addition to sponges, anemones also settle on other species of sponges (Petrosia, Agelas and Sarcotragus), on tunicates of the genus Microcosmus and on the yellow gorgonians Eucinella cavolinii and on the white Eucinella verrucosa.

When you put it to your ear, you can hear the sea breathing. The god Triton always carried it with him, playing it to calm the stormy sea and to announce the arrival of his father Poseidon, the god of the sea. The large shell was precious to every sailor, who used it to launch his call to signal the position of the vessel in the fog or to announce the arrival in port. That unmistakable sound also resounded in the countryside, to call the flocks and accompany the special moments of the communities. For millennia, the sea trumpet has been a tool for communication, alarm and even defense against attacks by enemy ships approaching the coast. All possible thanks to a shell, the largest in the Mediterranean after the noble pen shell and among the largest in the world, with a tapered conical shape and bright colors, from white to brown, under the marine encrustations. Inside, an enormous mollusc of about sixty centimetres, which bears the name of the half-man, half-fish god: Giant Triton, Charonia tritonis for science.

For tens of millions of years on the planet, fossils testify to its presence in all seas as other molluscs of the same Charoniidae family, with very similar characteristics that sometimes make them difficult to distinguish. It lives in the oceans and in the Mediterranean, from the east to the Adriatic, to the Sicilian Sea up to the central Tyrrhenian Sea, at a depth between twenty and forty meters. And it prefers rocky or detritus seabeds. Where it finds in abundance the invertebrates on which it feeds such as starfish, sea cucumbers and bivalves.

It mostly devours them whole, even when they are large, and digests them, even the hard parts, thanks to acid secretions produced by the salivary glands. The giant triton is also able to produce saliva that can paralyze its prey, in order to feed on it.

This also allows it to eat the large crown-of-thorns starfish (Acanthaster planci), which live in the Pacific and Indian oceans. Although their rays are covered with spines for protection, they are useless against the giant triton, their only predator. As such, it is considered essential for the defense of the coral reef, which in turn is prey to the crown-of-thorns starfish, which can feed on corals, thanks to powerful digestive enzymes. It is estimated that a single starfish can destroy six square meters of reef a year and the proliferation of crown-of-thorns is seriously endangering corals in various parts of the planet.

For its part, the giant triton has become quite rare in the Mediterranean, where sightings are very few. The population of the mollusc has been drastically decimated by the intensive fishing to which it has been subjected even in recent times both because it is edible and to use its precious shell, no longer as a foghorn or musical instrument, but for collecting purposes.

The giant triton is a species protected by the Bern and Barcelona Conventions, so fishing is prohibited.

A large protective umbrella and food, always and conveniently available.

It is the large jellyfish of the Mediterranean that ensure these benefits to some species of fish with which they have created a symbiotic relationship and from which they also benefit. Very different marine creatures, such as the astonishing Mediterranean Cassiopeia (Cotylorhiza tuberculata) and the horse mackerel (Trachurus trachurus), protagonists of one of the most characteristic examples of symbiosis offered by our sea. The jellyfish with the fascinating mythological name has a decidedly strange appearance and is so characteristic that it is unmistakable: observed from above, the umbrella appears like a large fried egg, with a bright yellow swelling surrounded by a white disk and is in fact also known as the "fried egg jellyfish".

The edge of the umbrella can take on a greenish color, indicative of the presence of tiny zooxanthellae algae, with which it also maintains a symbiotic relationship, like many other marine animals. Under the umbrella, which can reach thirty centimeters in diameter, like its other sisters belonging to the order of Rhizostomeae, it has arms with numerous ramifications in which the oral orifices through which it feeds are located. The arms, which end with small blue/purple buttons, are therefore not tentacles as in other species of jellyfish and, in the case of Cassiopeia, they do not have stinging cells, so they are also harmless to humans.

Among those filaments, small schools of young horse mackerel find a safe refuge from predators, which also take advantage of the protective jellyfish to easily stock up on food. The jellyfish, in turn, uses the small fish that follow to get rid of parasites and unwelcome guests.

The horse mackerel or suro belongs to the Carangidae family, therefore it is a pelagic bony fish, also present in the Mediterranean, as well as in the Atlantic Ocean and the North Sea. It lives mainly at great depths, up to a thousand meters, but it can also be found at lower depths, closer to the coast, in shady areas. The schools face seasonal migrations to find constant temperatures. The single specimen has an average length of about thirty centimeters, an iridescent green color, silver sides with a black spot on the operculum and one on the pectoral axil with gray dorsal fins, whitish anal and ventral fins, gray-green pectoral and ventral fins.

The symbiosis of juvenile horse mackerel, which are immune to the stinging liquid of jellyfish, does not only concern Cassiopeia, but also the other large jellyfish of the Mediterranean, the sea lung (Rhizostoma pulmo). The same is true for the juveniles of another carangid, the amberjack (Seriola dumerili), and fish of the Sparidae family such as salema (Sarpa salpa) and bogue (Boops boops).