Potamon fluviatile 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. 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 a stretch of river only long. In the Balkan Peninsula, "Potamon fluviatile" is known to occur in Croatia, Montenegro, the Republic of Macedonia, Albania and Greece. There are four species of "Potamon" in the Balkans, and "P. fluviatile" is replaced by "Potamon ibericum" in
Potamon fluviatile 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