When speaking of echinoderms, i.e., that group of sea animals usually equipped with “thorns on the skin”, we refer generally to the well-known sea urchins and starfishes. Just a few, instead, know that also crinoids (a.k.a. sea lilies), sea cucumbers and a special kind of “starfish”, if you really want to define them so, such as brittle stars (a.k.a. basket stars), are part of this family. Brittle stars, like stars, are made up of a central body where some arms graft, but there are quite clear differences between the two classes and some are easily detectable even at a superficial examination. The arms, for instance, are always very long compared to the body, serpentine and, among other things, devoid of ambulacral wrinkles. The pedicels then, when present, do not serve for locomotion as it happens for the stars and sea urchins, but serve rather to allow the perception and catching of food. Brittle stars move thanks to their very mobile and prehensile arms, which use as a handle every ground roughness and all kinds of submerged object. The effectiveness of such a model of locomotion is greater than one would think since the brittle stars are, in all respects, the faster echinoderms. Mostly sciaphilic, the brittle stars have nocturnal or crepuscular habits. During daytime, they usually refuge under rocks and in crevices, sometimes letting their long sensitive arms out, while they go out in the open at night. The voracity of these animals is well known among researchers: it is difficult to observe other invertebrates more insatiable and willing to swallow anything. With amazing regenerative abilities, especially for the speed with which they occur, almost all brittle stars have also the possibility of amputating arms, which remain easily into the clutches of the aggressor while the brittle star moves away quickly. Among all species of brittle stars, whose fundamental characteristics we have just analyzed, I want to tell you about one in particular. A brittle star that, although being very difficult to meet under water for its ability to provide natural camouflage and the deep environments where it hangs out at, deserves to be known for its, to say the least, charming appearance and its distinctiveness morphology and life habits. I am talking about the Astrospartus mediterraneus, also known as gorgon star because of its unique and curious look, which recalls the aspect of the Greek mythology’s goddess with thousands of snakes for hair.
The family gorgonocephalus, order eurialae (from Greek eurialae that, precisely, is the name of one of the Gorgons), includes brittle stars spread throughout the world, always with much branched arms. In the Mediterranean there is a single species as, among other things, tells us the Latin name. This usually lives over 50 meters deep, in sandy, muddy and / or rocky environments, often using the ramifications of colonial coelenterates like sea fans to settle more or less permanently. This brittle star keeps its arms mostly curled up on themselves, literally “rolled up” one by one, opening them only during the night for the capture of the food. This makes this animal’s look completely different when seen at night or during the day. We may notice such differences mainly in the Red Sea, where a very large species of this brittle star is easy to encounter because accustomed to climb up to very little depth overnight. The night dive will thus ensure the encounter with the tropical species, very beautiful with its unfolded arms, also because of its large size compared to the Mediterranean cousin. The Mediterranean gorgon star, to the contrary, is quite rare. Large just 40 cm in diameter with open arms, but with a charm all its own, perhaps due to the little information we have about its biology and the few images regarding it. Its tentacular arms, significantly branched from a short distance from the central disc, have the apices so much articulate and mobile that form a tangle where a precise form is difficult to distinguish. At first glance, one has the feeling of watching a confused hank of nylon or something like that. At closer examination, it turns out a fascinating animal instead…With the long arms extended, the gorgon star turns into a deadly trap for plankton, a tentacular network that extends over a broad surface and capable of filtering many cubic meters of water in the unit of time, variable in accordance with the size of the animal. Dissecting a gorgon star, in its stomach we may find copepods, larval crustaceans and fishes, annelids, shrimps and much more. Not that I ever picked up a single specimen to find out the contents of its stomach, but someone did it for study purposes, allowing us to understanding many things. All this variety of prey, however, is not passively filtered from the water, but captured with appropriate movements of the arms. The thin extremities are capable of grabbing the plankton, holding it through sharp hooks scattered on the joints and blocking it with layers of mucus. In this way, each arm becomes progressively a preys’ collection center, which the arm itself conveys periodically towards the mouth. Meanwhile all the other appendices are outstretched and in action, continuing throughout the night. The Gorgon star’s arms movements, appreciable after dark, immediately brings to mind those of crinoids’ feathered arms. In fact, such movements have the same goal: the capture of food. How they feed and what are the preferred preys of these strange brittle stars, we know from studies made on their relatives from outside the Mediterranean. The family gorgonocephalus is present from the surface up to about 2000 meters deep. Equipped with a small mouth and unable to bite or inoculate poisons, they join the dense range of filter feeders, using their intricate arms to capture what the sea currents incessantly convey. The best and richest currents must be sought carefully. This happens with clever movements of the star that, in the Mediterranean, lies fairly firmly on a gorgonian while in tropical seas takes refuge in the crevices to escape the daylight. Then, at night, it moves at the seabed to climb up, depending on the habitat, on coral pinnacles, sea fans, soft corals, sponges, sea pens or rock spurs more exposed to the currents. Generally, the marine biologist lacks the direct experiences in nature: in a nutshell, the practical observation. The underwater photographic documentation, highlighting some unedited natural aspects, provides irrefutable evidence of some moments of animal life. Speaking of experiences in the wild, I think it is important to report that I observed the specimens I have studied and documented in the sea of Scylla, at the northern border of the Straits of Messina, on some Aegadian’s shoals and only a few in the sea south of Leghorn, at Quercianella, where, however, the specimens I encountered were smaller than normal (small and medium size). These latter “Tuscans” Astrospartus were also found at less depths than usual, often in murky water because of the rocky and muddy seabed and of nearby rivers, although they are more common and often hosted by slender gorgonians of different species. On Scylla’s sea beds, where several shoals constituted by massive submerged mountains are covered with a dense network of sea fans, and lapped by strong and frequent currents, we may find the astrospartus below 45 m depth always “hugged” to the gorgonians. Same thing for the specimens found in the sea of Cape Milazzo, in Sicily, always clinging to red gorgonians or white eunicella starting from 30 m deep. Nevertheless, the true realm of this strange animal is the Argentario coast, where we may find many specimens even not very deep. In some cases, there are two or three specimens for each sea fan, starting from 25 or 30 m deep. Always nearby the Argentario cape, at the Middle Channel shoal, the number of astrospartus becomes really exaggerated: a unique show in the wild. I also identified and photographed many specimens in Liguria (Cinque Terre and Portofino promontory) although here the depth chosen by this species is much higher. A beautiful specimen found in the early nineties, on the seabed of Scylla (Strait of Messina, on the Northern Calabrian side), gave me the opportunity to follow his biology for about six years, being a little more than 50 meters deep in a convenient location, allowing me to return several times to visit it. One day it moved, changing sea fan and gaining a few meters deep. Then it disappeared forever, without a trace. A highly successful period, which lasted just over a year, saw me busy with a beautiful specimen, which I photographed and studied carefully, at only 39 m deep. The favorable position, which saw the Gorgon star anchored to a sea fan on the highest part of a medium sized rock, allowed me to achieve among other things beautiful images, even at night, the magic moment to observe the animal with its arms wide open. However, the artificial light, causing the closure of the arms, allows just enough time to make some shots before the animal takes back the typical aspect it keeps during daytime.
WORDS and PICTURES by Francesco Turano