The Pyramidellidae are a species-rich family of small gastropods which live as ectoparasites on other marine invertebrates. Their subtle variations around a quite homogenous basic morphology make species-level taxonomy extremely difficult. This volume (which is volume 200 in the parent series Mémoires du Muséum National d'Histoire Naturelle) contains the descriptions of 272 species collected in the last 30 years of deep-sea benthic exploration promoted by MNHN and IRD scientists. More than three-quarters of the species are new to science, and more is to come with the other genera to be studied following Turbonilla.
This paper takes a step forward towards answering some questions regarding the mega-diverse Indo-Pacific. What is really the order of magnitude of species richness? How are numbers of individuals distributed among species? How heterogeneous is the fauna on a geographic scale?
Anselmo Penas and Emilio Rolan have a considerable background in malacology, mostly European and Eastern Atlantic. Their venture with the Pyramidellidae started with the European and West African species, in a series of papers which appeared in the Spanish malacological journal Iberus, in which new species appeared by the dozens. The move to the Indo-Pacific goes up one order of magnitude, and only the great XIX century expeditions match similar numbers of new species introduced in a single paper.