[1] They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution.

The best known member is Marrella, with thousands of specimens found in the Cambrian aged Burgess Shale of Canada.

[2] Recent research has suggested the previously enigmatic Cambrian trilobite-like arthropods Skania and Primicaris belong to this group.

[2] Fragmentary taxa assigned to Marrellomorpha include Austromarrella from Cambrian Series 3 aged deposits in Australia,[4] and Dyrnwynia from the Ordovician (Darriwilian) aged Llanfallteg Formation of Wales, which in its original description was assigned to Marrelida.

[2] "Mimetaster" florestaensis Furca bohemica Mimetaster hexagonalis Tomlinsonus dimitrii Moroccan marrellid Marrella Palaeoisopus Haliestes Aquilonifer Vachonisia Xylokorys Enosiaspis Skania Primicaris Eoredlichia Mollisonia Waptia Tokummia Kylinxia