Margaretia is a frondose organism known from the middle Cambrian Burgess shale and the Kinzers Formation of Pennsylvania.

[1] Its fronds reached about 10 cm in length and are peppered with a range of length-parallel oval holes.

[2] It was later reclassified as a green alga closely resembling modern Caulerpa by D.F.

Satterthwait in her Ph.D. thesis in 1976,[3] a finding supported by Conway Morris and Robison in 1988.

[2] More recently, it has been treated as an organic tube, that is used as nest of hemichordate Oesia.