Some notes on Notodelphys rufescens Thorell, 1860, new to the Dutch Fauna

In September and October 1950, Mr. C. Swaneveld, of Zierikzee, and Mr. Jac. Viergever, of Serooskerke, collected some rich samples of Copepods, found alive in the branchial sac of certain species of Tunicates. The greater part of the Tunicates belonged to the Ascidian-species Ascidiella aspersa (O. F. Müller.) The peculiar little commensal lives in the branchial cavity, often in considerable numbers, with their posterior antenna fixed to the body wall of the Ascidian. The species of the genus Notodelphys stand lowest in the scale of species adapted to this curious mode of life : I observed them moving quickly through the water outside the Tunicate, in a jumping way. Especially when the water contains little oxygen, the animals leave their host through the ingestion opening. They do not swim for longer than a few seconds, then settling again on some object, often the outer wall of the Ascidian.