It is the most common animal represented in the Burgess Shale of British Columbia, Canada, with tens of thousands of specimens collected.

In 1971, Whittington undertook a thorough redescription of the animal and, on the basis of its legs, gills and head appendages, concluded that it was neither a trilobite, nor a chelicerate, nor a crustacean.

On the underside of the head was a pair of long and sweeping flexible antennae, composed of about total 30 segments, projecting forward at an angle of 15 to 30 degrees away from the midline.

[5][2] A 1998 paper suggested that striations present on the front projection of well-preserved specimens of Marrella represented a diffraction grating pattern, that in life would have resulted in an iridescent sheen.

[11][12] Marrella is likely to have been an active swimmer that swam close to the seafloor (nektobenthic) with its swimming appendages used in a backstroke motion, with the large spines acting as stabilizers, as well as possibly also having a defensive function.

A few dozen specimens of an indeterminate species of Marrella have been reported from the Kaili Formation of Yunnan, China, dating to the Wuliuan stage of the Cambrian.

A single fragmentary specimen of an indeterminate species is also known from the Balang Formation of Yunnan, China, dating to Cambrian Stage 4.