Hermit crabs are crustaceans in the superfamily Paguroidea.
This is a list of the largest metropolitan areas in Spain by population .. metropolitan areas. metropolitan areas. Spain. Spain. Estimates are from the following sources  :. the `` Functional Urban Areas '' -LRB- FUAs -RRB- of the Study on Urban Functions of the European Spatial Planning Observation Network -LRB- ESPON , 2007 -RRB-. European Spatial Planning Observation Network. European Spatial Planning Observation Network. the `` Larger Urban Zone '' -LRB- LUZs -RRB- of Urban Audit project -LRB- 2004 -RRB- , supported by the European Union .. European Union. European Union. Not all cities were included in this survey .. calculations by Francisco Ruiz from data of the Instituto Nacional de Estadistica -LRB- 2008 estimates -RRB- .. Instituto Nacional de Estadistica. Instituto Nacional de Estadistica ( Spain ). As well as `` metropolitan area '' data , Ruiz has produced larger conurbation data for some areas .. conurbation. conurbation. The `` conurbation '' figure is used where available , and is cited as such ; otherwise , the `` metropolitan area '' figure is used .. conurbation. conurbation. The figures differ between the reports due to the difference in survey dates and differences in methodology .. For example , ESPON considers Oviedo -- Gijon -- Aviles as a single FUA , while Urban Audit has separate LUZs for Oviedo and Gijon .. Oviedo. Oviedo. Gijon. Gijon. Aviles. Aviles. Similarly , Vilanova i la Geltru is included in Barcelona metropolitan area by ESPON , but as a separate conurbation by Ruiz .. conurbation. conurbation. Vilanova i la Geltru. Vilanova i la Geltru. Barcelona metropolitan area. Barcelona metropolitan area