moles_of_organic_mercury_per_unit_mass_of_zooplankton_expressed_as_carbon mol kg-1 [MLKG] The construction "moles_of_X_per_unit_mass_in_Y" is also called "molality" of X in Y, where X is a material constituent of Y. A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Organic mercury" describes a family of chemical species in which mercury atoms covalently bonded to carbon-containing groups, forming organomercury compounds (e.g., methylmercury (MeHg), monomethylmercury (MMHg), dimethylmercury (DMHg), ethylmercury (EtHg)). "Zooplankton" means the total zooplankton population, with components such as mesozooplankton, microzooplankton and miscellaneous zooplankton. The phrase "expressed_as" is used in the construction "A_expressed_as_B", where B is a chemical constituent of A. It means that the quantity indicated by the standard name is calculated solely with respect to the B contained in A, neglecting all other chemical constituents of A.