The worm stands upright and raises its spindled arms above its head as if giving a hearty ovation.

Researchers with the Royal Ontario Museum in Toronto detailed the 500-million-year-old critter for the first time in a study published Tuesday in the journal BMC Evolutionary Biology.

The bizarre creature, no bigger than a thumb, lived under water in a spot that is today a shale-strewn mountain ridge in British Columbia's Yoho National Park.

It has been dubbed Ovatiovermis cribratus, from the Latin "ovatio" meaning ovation and "vermis" meaning worm. Cribratus comes from "sieve" -- the study's authors believe the worm used its spiky forelimbs to comb through Cambrian waters for food particles.

Mystery how worm fended off predators

"We're not speculating if it was very happy or not, but it was waving its arms like someone doing an ovation, so we called it the worm that does an ovation — the ovation worm," said University of Toronto PhD candidate Cedric Aria, who co-authored the study.

Ovatiovermis had 18 limbs — four long spiky ones in front, eight shorter ones along its midsection and six stubby ones in the back with recurved claws, which are believed to have been used for anchoring.

Lead study author Jean-Bernard Caron, senior curator of invertebrate paleontology at the ROM, said it's a mystery how
Ovatiovermis would have defended itself from predators.

"This animal is completely naked, if I can say that. It doesn't have any spines or plates," said Caron, an associate professor at the University of Toronto.

"We obviously cannot prove it — and it's speculative at this stage --but one possibility is that it developed some sort of
coloration or toxicity that would have had an effect on potential predators."

Some resemblance to modern-day creepy crawlies

Ovatiovermis bears some resemblance to creepy crawlies populating the Earth today: arthropods, the largest category of animal life that includes insects, crustaceans and spiders. It also has some things in common with more obscure life forms such as the water bear and velvet worm.

There are two known Ovatiovermis specimens, both found in Walcott Quarry, one of the sites that make up the Burgess Shale.

The Burgess Shale, discovered more than a century ago, is a rich repository of Cambrian-age fossils and a UNESCO World Heritage Site.

The animals' squishy bodies, encased in sediment, enabled them to be preserved in the rock in striking detail.

The public can only access Walcott Quarry, in the B.C. Rockies about 200 kilometres west of Calgary, through pre-booked tours arranged by Parks Canada or the Burgess Shale Geoscience Foundation.

Participants are warned that removing fossils from the site is against the law.

Creature sat unexamined for more than 2 decades

The first Ovatiovermis specimen was found in 1994, but the ROM's fossil collection is so vast that researchers didn't get around to examining it until more than two decades later.

Caron had just wrapped up a paper about it last year when he went on a Burgess Shale hike and Parks Canada staff showed him an unusual fossil a visitor came across in 2011.

He recalls jumping at the sight of it. 

"This second specimen nicely confirmed our interpretations of the morphology of the animal, and it shows that serendipity can sometimes help researchers in strange ways. The visitor who found that second specimen was certainly very, very lucky," said Caron, who added the paper was revised to include the second specimen.

"What are the odds of finding such a rare animal on a casual guided hike, while teams of researchers in the past 100 years found only one during extensive quarrying operations?"