Lophophorates are a group of sea creatures with a shady history.
|Wufengella (illustrated) is an armored worm that may be the common ancestor of a diverse group of marine invertebrates. PALEOCREATIONS.COM/ROBERTS NICHOLLS|
An ancient armored worm could hold the key to understanding the evolutionary history of a diverse group of marine invertebrates.
A 520-million-year-old fossil of the newly identified worm, dubbed Wufengella, discovered in China, maybe the missing link between three of the phyla that comprise a cadre of sea creatures known as lophophorates.
According to genetic analysis, Wufengella is most likely the common ancestor of brachiopods, bryozoans, and phoronid worms, report paleontologist Jakob Vinther and colleagues in Current Biology on September 27.
"We were thinking [the common ancestor] might have been some wormy animal with plates on its back," says Vinther of the University of Bristol in England. "However, we never had the animal."
Nearly all major animal groups appeared on the scene roughly half a billion years ago in a flurry of evolutionary diversification known as the Cambrian explosion (SN: 4/24/19). Lophophorates experienced rapid species growth during this period, which obscured the group's evolutionary history.
|This Wufengella fossil, discovered in China, is approximately 520 million years old and shares several characteristics with sea creatures known as lophophorates. LUKE PARRY AND JAKOB VINTHER|
One feature that unites the group's various phyla is their tentacle-like feeding tubes known as lophophores. Aside from that, the phyla are all quite different. Brachiopods are shelled animals that resemble clams at first glance. Bryozoans, also known as moss animals, are microscopic sedentary organisms that live in coral-like colonies. And phoronids, also known as horseshoe worms, are soft-bodied, unsegmented creatures that live in stationary, tubelike structures.
(Recently, researchers determined that hyoliths, an extinct animal known for its conical shells (SN: 1/11/17) — are also lophophorates due to the tentacled organ that surrounds their mouth.)
Vinther and his colleagues discovered that Wufengella does not belong to any of these phyla. However, the critter shares characteristics with brachiopods, horseshoe worms, and bryozoans, including a series of asymmetric, armored back plates, a wormlike body, and bristles that protrude from lobes surrounding its body.
According to Gonzalo Giribet, an invertebrate zoologist at Harvard University who was not involved in the research, the fossil is a "great find." Nonetheless, he cautions that the scientists' analysis does not prove that Wufengella is the long-sought missing link, but rather suggests it.
Some researchers hypothesized that lophophorates' common ancestor would have been a stationary creature that sat on the seafloor and fed only through tubes, similar to their modern relatives. According to the researchers, the Wufengella fossil could refute this theory; the animal's body plan suggests that it crawled around.
Vinther's bucket list of fossils that he and his colleagues hoped to find had long included Wufengella. But, he says, "we always thought, 'Well, we probably won't see that in real life.'" Normally, such a creature would have lived in shallow water. Organisms do not fare well there, decaying quickly due to the abundance of oxygen. Vinther believes that the Wufengella that his team discovered was washed out to deep water during a storm.
The researchers hope to find more Wufengella now that they've discovered one, in part to see if there are other varieties. And, according to Vinther, the team may be able to identify even more distant ancestors further back on the tree of life that connect lophophorates with other animal groups such as mollusks, further fleshing out how life on Earth is connected.