n. The plants and animals that live in the sea-bottom, and those that are attached to its surface, and those that creep or run over it: a collective noun introduced by Haeckel. The benthos is contrasted with the plankton, or floating and swimming fauna and flora of the sea. It includes all the marine macrophytic algæ, also some phanerogams, the sea-grasses (see sea-grass, 1), as well as an abundance of microphytic algæ (diatoms, etc.). It is divided into the sedentary and the vagile or vagrant benthos, the former including organisms attached to the bottom, the latter those moving over it. See plankton, nekton.