Potamon fluviatile

Adult Potamon fluviatile may reach a carapace length of , with females being generally smaller than males. As with other crabs, the body is roughly square, with the reduced abdomen tucked beneath the thorax. The thorax bears five pairs of legs, the first of which is armed with large claws. The life span of P. fluviatile is typically 10–12 years. Mating lasts between 30 min and 21 hours, with spawning usually taking place in August. Females carry the eggs on their pleopods (appendages on the abdomen) until they hatch directly into juvenile crabs, having passed through the larval stages inside the egg. More recently, the species was depicted on the 5¢ coin in the last series of Maltese coins before the introduction of the Euro there in 2007. == Ecology ==

Potamon fluviatile has a generalist diet, feeding on vegetable debris, scraping algae from surfaces, or preying on frogs, tadpoles, and various invertebrates, such as insect larvae, snails or worms. Non-indigenous crayfish may pose a greater threat to P. fluviatile than native crayfish, although the greatest threats remain pollution, overfishing and the draining of wetlands. ==Distribution==

, near Sparta – habitat for Potamon fluviatile|alt=A fast-flowing river in a wide, gravelly bed, flows through woodland. The natural range of Potamon fluviatile is highly fragmented, and covers parts of many countries with a Mediterranean coastline. It is found in mainland Italy and on the Balkan Peninsula from Dalmatia to the Axios River in Greece. In 1997 a population of P. fluviatile was discovered under the ruins of Trajan's Forum in the heart of Rome, living in canals built by the Etruscans which connect to the Cloaca Maxima. Based on a genetic analysis, which demonstrated that these crabs were similar to those in Greece, researchers believe that they had been brought by the Greeks before the founding of the city, some 3000 years ago. The crabs' unusual size, up to , and longevity (up to 15 years) are also interpreted as evidence of a long-established population, by analogy with island gigantism. Malta On the island of Malta, Potamon fluviatile is rare and restricted to a few locations in the west of the island. On Gozo, there is a single population which inhabits part of a valley only long. In mainland Greece, P. fluviatile is found in the drainages of the Axios, Thyamis, Aheron and Arachthos, Pineiós, Piros-Tethreas, Pamisos and Evrotas rivers. In the Ionian Islands, P. fluviatile is known to occur at only one site on Corfu, as well as on Kefalonia, Lefkada and Zakynthos. In the Aegean Islands, it is found on Skiathos and Skopelos (Sporades), on Euboea and Skyros, and at a single site on Andros in the Cyclades. ==Taxonomy==

Potamon fluviatile is at the western distributional limit of the genus Potamon. Other species in the genus occur through Eastern Europe and the Middle East, and across Central Asia as far east as northwestern India. The populations of P. fluviatile on the Peloponnese, Kefalonia, and Zakynthos may represent a separate, cryptic species, P. fluviatile was formerly divided into three subspecies: P. f. algeriense, P. f. berghetripsorum and P. f. fluviatile. The first two of these live in North Africa, and were later combined and separated from P. fluviatile as the species Potamon algeriense. By 1983, the nominate subspecies (equivalent to the current circumscription of the species P. fluviatile) had been divided into six nationes, or "tribes". Natio fluviatilis was found in northern Italy, natio tarantium in southern Italy, and nationes thessalonis, kühnelti and laconis were found in parts of Greece. The geographical distribution of natio leucosis was not reported, and it was suggested that a further (undescribed) tribe inhabited the Greek island of Andros. Despite this wealth of infraspecific taxa, they are rarely used by scientists, and some have questioned directly the value of defining infraspecific taxa within P. fluviatile. In 1990, the population on Malta was described as a separate subspecies, Potamon fluviatile lanfrancoi, and that taxon has become a conservation icon in Malta following its legal protection in 1993, although not all scientists recognise the taxon. ==References==