Myriapoda (Myriapods) is a subphylum of arthropods. There are 18965 species of Myriapods, in 3261 genera and 178 families. It includes groups like Millipedes, Centipedes, and Symphylans.
Definition: number of currently described and taxonomically accepted marine species in this clade (Appeltans et al. 2012. The Magnitude of Global Marine Species Diversity. Current Biology 22, 2189–2202. http://dx.doi.org/10.1016/j.cub.2012.09.036)
Definition: Any material within 2 m from the Earth's surface that is in contact with the atmosphere, with the exclusion of living organisms, areas with continuous ice not covered by other material, and water bodies deeper than 2 m.