In 1996 a sponge was found in a well studied area in the Ria of Etel, Brittany, France, that had never been recorded there before. This sponge was later described as a new species and genus, Celtodoryx girardae by Perez et al. (2006), who concluded that it is probably an invasive species. Over several years C. girardae was found to occur successively in the Gulf of Morbihan, France, and Oosterschelde estuary, Netherlands. This sponge is characterized by an extensive spatial broading and therewith it rates today among the dominant benthic megafauna in the shallow waters of the Gulf of Morbihan and Dutch inshore waters. During our recent survey of the Chinese Yellow Sea sponge fauna, we found an abundant species with close morphological similarities to C. girardae. Further taxonomic studies have revealed that both the Chinese and European sponges are in fact conspecific with Cornulum ciocalyptoides described by Burton (1935) from Posiet Bay, Sea of Japan and later recorded from other localities of the North West Pacific (e.g. Koltun, 1971; Sim & Byeon, 1989). In this paper we transfer the species of Burton from Cornulum to Celtodoryx and consequently it becomes the senior synonym of C. girardae. Furthermore, we conclude that Celtodoryx ciocalyptoides was introduced to the North East Atlantic from the North West Pacific with aquaculture of the Pacific oyster Crassostrea gigas as the probable vector. This is probably the first case recorded so far of a sponge species being transferred from one ocean to another by human activity.