Margaretia is a frondose organism known from the middle Cambrian Burgess shale

Burgess Shale

The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...

. Its fronds reached about 10 cm in length and are peppered with a range of length-parallel oval holes. Its original interpretation as a green alga is not secure; it also resembles some alcyonarian

Alcyonarian

The Alcyonarian corals are organisms resembling the octocorals . This individual polyps formed colonies and bore sclerites. The Burgess shale organism Margaretia dorus resembles an Alcyonarian, according to C.D. Walcott , and was reclassified as green algae closely resembling modern Caulerpa by...

 coral

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

s, but a thorough redescription will be necessary to securely classify it. A relationship with the modern green Caulerpa

Caulerpa

Caulerpa is a genus of seaweeds in the family Caulerpaceae . They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world...

is the most up-to-date consideration.