Nematodes have been identified as a potentially hyperdiverse group and the deep sea as a potentially hyperdiverse environment (i.e. > 1 million species). A large‐scale data set from the equatorial central Pacific is used to estimate regional diversity with results that challenge this view; regional diversity is higher in some coastal waters despite lower sample diversity in coastal waters than in the deep sea. The data suggests a paradigm where the deep sea has modest regional diversity, despite high local diversity through patch dynamics, because similar patches in a similar habitat are repeated for considerable distances. Disturbance in shallow water dominates over patch‐dynamic mechanisms reducing local diversity but regional diversity is high because of the close packing of multiple habitats within a single region.  The Pacific data are also used to demonstrate the pitfalls of extrapolating from local to global diversity. There is no reason to conclude that nematodes are less diverse than other benthic groups, indeed where direct comparison is possible the Nematoda appear to be as diverse as the Polychaeta, the most diverse macrofaunal taxon. This analysis is not consistent with the hypothesis that either marine nematodes or the deep‐sea benthos are hyperdiverse raising the question whether any environment or metazoan taxon has more than a million species.

Abstrac~ Little is known about the biodiversity of free-living nematodes. We have attempted to provide baseline information about the natural diversities (those not influenced by pollution) that might be expected in six biotopes. Seventeen marine nematode data sets consisting of 197 samples were standardized to allow a comparison of alpha diversity, or sample diversity, from temperate estuarine, tropical sublittoral, temperate sublittoral, bathyal, abyssal, and hadal biotopes, which were selected on criteria of depth and latitude. The diversity analysis methods we employed were rarefaction curves; three weighted diversity indices of species ric~ ness, SR, H', and ES(X); and two equitability indices, J' and V. Diversity was significantly different in the six biotopes. The weighted indices of species richness were more capable of resolving differences between the biotopes than were the equitability indices, whose large standard errors suggested that they were more influenced by local, small-scale ecological factors. This suggests that species richness is a better measure than equitability for large-scale comparisons of biotopes or regions. The ES(X), which is robust to sample size variations, was more efficient than the weighted indices of species richness, which were easily influenced by sample size. There was a nonlinear relationship between depth and diversity with the bathyal and abyssal biotopes displaying the highest diversity. The tropical subltttoral biotope was not more diverse than the temperate sublittoral biotope. The lowest diversities were found in the physically challenging temperate estuarine and hadal biotopes.Biodiversidad ecol6gica de los nematodes marinos en muestras de regiones templadas, tropicales y de aguas profundas.Resumen: Poco se conoce acerca de la biodtversidad de los nemdtodos. En este estudio intentamos proveer informaci6n bdlsica acerca de las diversidades naturales (es decir no influenciadas por la contaminaci6n) que deberian observarse en sets biotopos. Se estandarizaron 17 grupos de datos de nemdtodos marinos, de 197 muestras, para permitir la comparaci6n de la diverstdad alfa (diversidad muestral) de los siguientes biotopos, selecclonados en base a criterios de profundidad y latttud: estuarinos templados, sublitoral tropical, sublitoral templado, batlal, abisal y hadaL Los M~todos de andlisis de diversidad que empleamos fueron curvas de rarefacci6n, tres indices de riqueza de espectes, SR, H ~, y ES(X); y dos indices de equttabilidad, J' y V. La diversidad diferente significativamente entre los seis bi6topos. Los indices de riqueza de especies resolvieron mejor las diferencias entre los biotopos que los indices de equttabiltdad, cuyos grandes errores estandar sugirieron que son mds influenciados por factores ecol6gicos locales de peque~a escala. Esto sugtere que la riqueza de especies es una mejor medtda que la equitabilidad para comparaciones de bt6topos o regiones a gran escala. El indice ES(X) que es robusto en cuanto a variaciones en el tama~o de meustra de, Sue mds eftclent...

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