Occurrence of the European ascidian Ascidiella scabra (Müller, 1776) in the 19 century in Nagasaki, Japan, probably as an ephemeral alien species

Abstract

The generic affiliation of the single Japanese record of the ascidian genus Ascidiella, as "A. virginea (Müller)" by Hartmeyer in 1902, was questioned by Nishikawa in 1995 because of the genus's natural distribution being confined to Atlantic waters, the somewhat confused history of taxonomy in the genus and allies, and of the insufficient description. Our personal reexamination of the material collected from Nagasaki and deposited in the Museum für Naturkunde der Humboldt-Universität zu Berlin reveals that it is identical to Ascidiella scabra (Müller, 1776), so far recorded exclusively from European boreal to warm-temperate waters. Combining imperfect label information of the material with historical knowledge, the material is supposed to have been collected in February, 1861, by Mr. Otto Schottmüller, a member of the Prussian East Asia Expedition led by Graf zu Eulenburg. It is proposed that the material probably represents an ephemeral population of an alien species.