On the occurrence of Carcinus maenas (Linnaeus) and its parasite Sacculina carcini Thompson in Burma, with notes on the transport of crabs to new localities

From time to time crabs have been found in localities at great distances from their normal area of distribution, owing to their being transported by ships in ballast water tanks or on the hulls. Much attention has been paid to a report by Catta (1876), who examined the Crustacea taken from the hull of a ship that had made the voyage from India to Marseilles. Among these, four species of crabs of the family Grapsidae were represented, one of which, named by him Plagusia squamosa, being present in hundreds of specimens. Catta saw here the possibility of an extension of the area of distribution of the crab, but apparently the conditions of life were not favourable in the new locality, and the crab did not become established here. Stebbing (1893: 99) remarks that the correct name of the crab referred to above is Plagusia depressa (Fabricius) and adds that "The point of special interest, however, lies, as Catta explains, in showing the effects on distribution that may be produced by unconscious human agency." The data mentioned above were recorded again by Chilton (1911). According to Bennett (1964: 87) lists as given by Stebbing and Chilton of species transported on the hulls of ships are not lists of accidental acclimatisations, for it does not follow that the crabs could establish themselves in their new homes. Another case of unsuccessful transport of a crab to a new locality is the record of great numbers of Pilumnus spinifer H. Milne Edwards at Uddevalla harbour on the west coast of Sweden in 1826 (Christiansen, 1969: 77). Here undoubtedly the crab disappeared because it could not stand the cold in its new locality. A diligent search in the literature certainly would reveal numerous other