Further examination of this extremely early soft-bodied animal known as a fuxianhuiid also uncovered the oldest nervous system to stretch beyond the head in fossil record, they said.
The analysis was made possible by an extraordinary fossil find in China, the University of Cambridge reported Wednesday.
Until now, all fossils found of fuxianhuiids featured heads covered by a wide hard shell or "carapace." obscuring underlying contents from detailed study.
But in some of the fossils found in South China, the creatures had been flipped over before they were fossilized, allowing scientists to examine the heads closely.
Paleontologists found limbs under the head used to shovel sediment into the mouth as the fuxianhuiid crawled across the seabed, millions of years before life emerged from the oceans.
This could be the earliest example of manipulative limbs used for feeding purposes, they said, hinting at the adaptive ability that made arthropods so successful and abundant, evolving into the insects, spiders and crustaceans of today.
The fossils also revealed the oldest nervous system yet found that is "post-cephalic" or beyond the head.
Fuxianhuiids existed around 520 million years ago, about 50 million years before primordial land animals crawled from the sea.