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The Mediterranean deep sea, being isothermal and longitudinally trophic-graded, is an optimal natural benchmark to test for macro-ecological patterns of species distribution. The relevance of environment−biota interactions on deep-sea megafauna in the Mediterranean Sea, a matter still neglected, is addressed here along longitudinal and bathymetric axes. Benthic and nektobenthic megafauna were collected in the 3 basins of the Mediterranean: the western (Catalan Sea and southern Balearic), central (western Ionian) and eastern (south of Crete) basins, with an otter-trawl Maireta system and an Agassiz dredge between 1200 and 4000 m depth. Simultaneously, environmental data were collected on surface production, near-bottom physical parameters, sediment grain size and carbon content. Megafaunal biomass was higher in the Catalan Sea, decreasing eastward and with depth. Species diversity and evenness were relatively constant in the western and central Mediterranean at all depths, whereas these indices decreased with depth in the eastern Mediterranean. β-diversity analyses indicated a high species turnover between areas. The 3 basins presented significantly different environmental conditions. Sediment particulate organic carbon, surface fluorescence and sediment grain size were the 3 environmental variables that best explained the distribution of megabenthos along the longitudinal Mediterranean axis. These results show that the food supply, from either the surface or from the adjacent deepsea floor, is critical in regulating the biodiversity of deep-sea Mediterranean megafauna and that this diversity is pooled region-wide. The heterogeneity of resources may be essential in maintaining these high levels of local and regional diversity.

Summary:This study provides a compilation of all available information on deep-sea echinoderms from the middle and lower slopes of the Mediterranean Sea, with the aim of providing a unified source of information on the taxonomy of this group. Previous records of species are updated with new data obtained from 223 trawl hauls conducted in 11 cruises within the northwestern Mediterranean Sea between 800 m and 2845 m depth. Valid names, bathymetric ranges and geographic distributions are given for all species. The new data report, for the first time, the presence of the Atlantic echinoid Gracilechinus elegans (Düben and Koren, 1844) in the Mediterranean Sea. We also report the presence of the endemic holothurians Hedingia mediterranea (Bartolini Baldelli, 1914), dredged only once previously in 1914 in the Tyrrhenian Sea, and Penilpidia ludwigi (von Marenzeller, 1893), known previously only from three samples, two in the Aegean Sea and one in the Balearic Sea. Additionally, the deeper limits of the bathymetric distribution of four species have been expanded: the asteroid Ceramaster grenadensis (Perrier, 1881) to 2845 m; the echinoid Brissopsis lyrifera (Forbes, 1841) to 2250 m; and the holothurians Hedingia mediterranea and Holothuria (Panningothuria) forskali Delle Chiaje, 1823, to 1500 m and 850 m, respectively.Keywords: deep-sea echinoderms; Mediterranean Sea; Gracilechinus elegans; submarine canyons; taxonomy; bathymetric range. Primera cita, redescubrimiento y recopilación de los equinodermos de profundidad en el talud continental medio e inferior del MediterráneoResumen: Este estudio presenta una recopilación de toda la información disponible sobre los equinodermos de profundidad en el talud continental medio e inferior del mar Mediterráneo, con el fin de proporcionar una fuente de información unificada sobre la taxonomía de este grupo. Se han actualizado los registros anteriores mediante nuevos datos provenientes de 223 pescas de arrastre de 11 campañas oceanográficas realizadas en el noroeste Mediterráneo entre 800 y 2845 m de profundidad. Se ha actualizado el nombre de las especies, sus rangos batimétricos y sus distribuciones geográficas. Los nuevos datos presentan, por primera vez, la presencia del equinoideo Atlántico Gracilechinus elegans (Düben and Koren, 1844) en el mar Mediterráneo. También se cita la presencia en el noroeste Mediterráneo de dos especies de holoturias endémicas del Mediterráneo, Hedingia mediterranea (Bartolini Baldelli, 1914)

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