The tentaculate ctenophore Pleurobrachia pileus (O.F. Muller), its morphology, life history, helminth and nematode parasites

Abstract

Aspects of the biology of Pleurobrachia pileus (O.F. Müller 1776), are given including its distribution in New Zealand waters, its seasonal occurrence in Kau Bay, Wellington Harbour, its life history, and trematode and nematode parasites. The morphology, histology, and some histochemistry of the organ systems is described. A new terminology for regions of the gastrovascular system is proposed. The origin and structure of the middle layer is discussed and the term mesoderm is recognised in place of mesogloea for this germinal layer. Three distinct forms of trematode larvae are described from P. pileus. Trematodes occurred more frequently than nematodes in approximately the ratio of 3:1. Trematodes taken were all late larval, but non encysted metacercarian stage of development. They are assigned to Tergestia agnostomi Manter 1954, Lecithocladium excisum (Rud., 1819), and ? Pseudocreadium Layman 1930. These trematode genera have not previously been recorded from a ctenophore. All the nematode larvae are assigned to the Fam. Ascaridae Cobbold 1864, and the genus Contracaecum. Railliet and Henry 1912. Larvae of Contracaecum have not previously been recorded from a coelenterate host.