Traditionally gelatinous predators were thought ineffectual providers of marine trophic pathways, but they appear to have substantial and integral roles in deep pelagic food webs. Pelagic siphonophores, a diverse group of cnidarians, are found at most depths of the ocean - from the surface, like the Portuguese man of war, to the deep sea. They play important roles in ocean ecosystems, and are among the most abundant gelatinous predators. Jelly pump Biological oceanic processes, primarily carbon production in the euphotic zone, sinking and remineralization, govern the global biological carbon soft‐tissue pump. Sinking and laterally transported carbon‐laden particles fuel benthic ecosystems at continental margins and in the deep sea. Marine zooplankton play a major role as ecosystem engineers in coastal and open ocean ecosystems because they serve as links between primary production, higher trophic levels, and deep‐sea communities. In particular, gelatinous zooplankton (Cnidaria, Ctenophora, and Chordata, namely, Thaliacea) are universal members of plankton communities that graze on phytoplankton and prey on other zooplankton and ichthyoplankton. They also can rapidly reproduce on a time scale of days and, under favorable environmental conditions, some species form dense blooms that extend for many square kilometers. These blooms have negative ecological and socioeconomic impacts by reducing commercially harvested fish species, limiting carbon transfer to other trophic levels, enhancing microbial remineralization, and thereby driving oxygen concentrations down close to anoxic levels. Jelly carbon The global biomass of gelatinous zooplankton (sometimes referred to as jelly‐C) within the upper 200 m of the ocean amounts to 0.038 Pg C. Calculations for mesozooplankton (200 μm to 2 cm) suggest about 0.20 Pg C. The short life span of most gelatinous zooplankton, from weeks up to 2 to 12 months, suggests biomass‐production rates above 0.038 Pg C year−1, depending on the assumed mortality rates, which in many cases are species‐specific. This is much smaller than global primary production (50 Pg C year−1), which translates into export estimates close to 6 Pg C year−1 below 100 m, depending on the method used. Globally, gelatinous zooplankton abundance and distribution patterns largely follow those of temperature and dissolved oxygen as well as primary production as the carbon source. However, gelatinous zooplankton cope with a wide spectrum of environmental conditions, indicating the ability to adapt and occupy most available ecological niches in a water mass. In terms of Longhurst regions (biogeographical provinces that partition the pelagic environment, the highest densities of gelatinous zooplankton occur