||P.297 right column bottom paragraph: "Marine sponges are widely considered the most primitive of the metazoans, arising at least as early as the Precambrian, some 600 million years ago (primary source). According to molecular clocks, the divergence of sponges from the ancestors of other metazoans may have occurred even earlier, around 1.3 billion years ago (ref 144). During subsequent periods of the Paleozoic era, sponges accounted for much of the biomass on marine reefs (refs 167, 491). Today, they remain important members of both shallow- and deep-water communities, occupying as much as 80% of available surfaces in some areas (ref 74). Such sustained evolutionary and ecological success is probably due, at least in part, to their intimate associations with microbial symbionts."