The biology of a commensal copepod,Ascidicola roseaThorell, in the ascidianCorella parallelogramma(Müller)

Abstract

A study has been made of the feeding activities and reproductive behaviour of the copepodAscidicola roseawithin one of its ascidian hosts,Corella parallelogramma.Ascidicola roseafeeds on particles which it removes from the food string as the latter is passing through the oesophagus of the host. When active feeding is not taking place, the copepod remains quiescent in the oesophageal bend. An inverted position within the oesophagus is sometimes adopted; this is generally associated with a meagre development of the food string. Certain peculiar structural features—notably the spinous pad on the penultimate segment and the long endopodal setae—are considered to be adaptations which assist the copepod while clinging to the food string.The eggs ofA. roseaare deposited in the ascidian's stomach and the nauplii pass through the host's alimentary canal still enveloped by the inner egg membrane. On reaching the anus, hatching takes place and the nauplii are expelled from the atrial siphon. There are four naupliar and two copepodid stages. Free-swimming life lasts for about 6 days.