On the identity of Hydroides priscus Pillai 1971 - Taxonomic confusion due to ontogeny in some serpulid genera (Annelida: Polychaeta: Serpulidae)

We introduce the concept 'bioperculate chimaera' for an ontogenetic stage in the genus Hydroides having two different two-tier opercula, one a small operculum with simple (un-differentiated) spines - an H. 'priscus'-type - present on the opposite branchial lobe from an operculum characteristic of Hydroides cf. albiceps, or H. cf. brachyacanthus, or H. diramphus, H. homoceros, H. minax, H. trivesiculosus, or as of yet undiscovered additional taxa. An additional and presumably more advanced bioperculate chimaera stage has been found in Hydroides cf. albiceps. Documentation is provided of the 'new', immature, two-tier opercular stage and of these different chimaeras; their biogeographic affinities are discussed. Some concepts of Hydroides opercular ontogeny and function are reviewed, with remarks on taxono-mic errors deriving from unawareness of variability within populations.