Species differentiation in Synidotea (Isopoda: Idoteidae) and recognition of introduced marine species: A reply to Chapman and Carlton

Nominal species of the idoteid isopod genus Synidotea from Japan (S. laevidorsalis), western U.S.A. (S. laticauda), South Africa (S. hirtipes), and Australia (S. keablei and S. grisea) are shown to be morphologically distinct. Others probably are also. Contrary to the views of Chapman and Carlton (1991, 1994), the Japanese species has not been widely distributed by shipping. The Australian species fail several of Chapman and Carlton's attributes of introduced species: their recent discovery and restricted distribution are anticipated in a poorly explored fauna, there is no evidence of postintroduction range extension, no known human mechanisms of introduction exist, they are not associated with known introductions, nor with altered environments, and exotic evolutionary origin cannot be assessed while the phylogeny of the genus is not known. The species in the western U.S.A. is ecologically as well as morphologically distinct, being estuarine rather than marine. A record of S. laevidorsalis from the Gironde estuary, France, is, in fact, of S. laticauda and therefore an introduction from the U.S.A. rather than from Japan. This study demonstrates the importance of careful taxonomic analysis before it is concluded that marine species are introduced.