The distribution, origins and taxonomy of Tricellaria inopinata d'Hondt and Occhipinti Ambrogi, 1985, an invasive bryozoan new to the Atlantic

Populations of the invasive cellularine bryozoan Tricellaria inopinata d'Ho ndt and Occhipinti Ambrogi have recently (August 1998) been identified from the coast of southern England, representing the first Atlantic records for this taxon. Although first named from material collected in the Venice Lag oon in 1982, T. inopinata was subsequently identified as invasive there and of unspecified Pacific origin. An appraisal of samples and literature from various global regions suggests that Atlantic and Adriatic T. inopinata co rrespond with a morphospecies known to be invasive in New Zealand, and cryp togenic in Pacific North America, Japan and Australia. The morphospecies in question has usually been referred to as T. occidentalis (Trask, 1857) and in at least one instance as T. porteri (MacGillivray, 1889). Morphological comparisons, however, indicate that Adriatic, Atlantic and putative T. ino pinata from the Pacific differs morphologically from early descriptions and specimens of T. occidentalis from Pacific North American waters and T. por teri from Australia. This study confirms the Pacific origins of Adriatic an d Atlantic T. inopinata. Its widespread Pacific distribution and the possib ility of anthropogenic dispersal there in historical times precludes the mo re precise identification of its source region. There is also a possibility that T. inopinata represents a hybrid between Pacific morphospecies united by anthropogenic translocation.