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Image Gallery: A Worm Missing Link

Burgess Shale Worm

Acorn worm fossil from Burgess shale

(Image credit: JB Caron)

A fossilized Spartobranchus tenuis from the Burgess shale in Canada. The animal contains features of modern acorn worms and modern tube worms called pterobranches.

Spartobranchus tenuis

Spartobranchus tenuis in a tube

(Image credit: JB Caron)

Spartobranchus tenuis in a tube. The worms look like modern free-living acorn worms, but resided in tubes. Modern mini-tube worms called pterobranches may have evolved from worms like this.

Acorn Worm

Acorn worm in modern form

(Image credit: C.B. Cameron)

The modern acorn worm Harrimania planktophilus. The acorn worms are about 1.2 inches (32 millimeters) long when uncoiled.

Undescribed Acorn Worm

Acorn worm in modern form

(Image credit: C.B. Cameron)

A modern-day acorn worm about 3.5 inches (88 mm) long.

Modern Pterobranch

Pterobranch worm colony

(Image credit: C.B. Cameron)

A modern pterobranch, Rhabdopleura normani. Each of these tube-dwelling worms is only 0.02 inches (0.5 mm) long.

Modern Tubes

Tube colony of pterobranches

(Image credit: C.B. Cameron)

A modern tubular colony created by pterobranches. These tubes are similar to those seen fossilized in the Burgess shale.

Worms Illustrated

Spartobranchus tenuis in a tube

(Image credit: Marianne Collins)

A reconstruction of Spartobranchus tenuis within and outside of their tubes.

Worm in Tube

Spartobranchus tenuis in a tube

(Image credit: Marianne Collins)

A close-up of Spartobranchus tenuis in its tube.

Burgess Shale

Burgess Shale in British Columbia

(Image credit: JB Caron)

The Burgess shale in Yoho National Park, British Columbia, where the Spartobranchus tenuis fossils are found.

Burgess Shale

Burgess shale quaries

(Image credit: J. Niddrie Photo, courtesy of Parks Canada)

Burgess shale quarries on Fossil Ridge in Yoho National Park.

Burgess Fossil Quarry

Burgess Shale in British Columbia

(Image credit: J. Niddrie Photo, courtesy of Parks Canada)

A close-up of a fossil quarry in the Burgess shale in Yoho National Park.