Extended Data Fig. 1: Maps and plots of collection and sequencing effort.

a, Map of sample sites across the study area, with land masses defined using the ETOPO1 dataset⁶². The study area, a trapezoid shape on this geographical projection, contains equal area polygons per latitude spaced either side of 150° E. Red dots indicate shallow sites (0–200 m), green dots indicate samples obtained from the upper to mid-bathyal (200–2,000 m) and blue dots indicate samples from the lower bathyal and abyss (>2,000 m); many sites overlap. Sampling over our study area is concentrated around continental margins with few expeditions to the abyssal plain or mid-ocean ridges. b, Collection effort (for example, the numbers of trawls, dredges or submersible collections) over our study area is, as expected, highest in shallow water (0–100 m) followed by cells at upper to mid-bathyal depths. Variation in collection effort does not explain the latitudinal and bathymetric gradients in species richness for this data⁸. Although collection effort is much lower at lower bathyal and abyssal depths (2,000–4,000 m), this is offset by a general increase in the size of observed species ranges with depth. Many abyssal ophiuroids are widespread across temperate and tropical latitudes. c, The percentage of species with DNA data is high (>70%) over the entire study area, except below 2,000 m across tropical latitudes (mean, 52%; minimum, 41%). However, these depths are relatively species-poor and sequencing effort across the entire tropical deep-sea biome (as defined in Fig. 1g) exceeds 70%.