In the published version of this article (Ramirez-Guerrero et al., Reference Ramirez-Guerrero, Alghaled, Bateman, Cournoyer and Cameron2026), the term stem-group was incorrectly applied in the phylogenetic context of some fossil taxa. Specifically, Conicula is the only stem medusozoan recovered in our analysis. Paleocanna should be referred to as a stem-group taxon of the clade Acraspeda Gegenbaur, 1856 (including Staurozoa, Cubozoa, and Scyphozoa). Fossil taxa referred to in the original article as ‘stem-medusozoan’ in the introduction are now interpreted as basal crown medusozoans, representing extinct forms that diverged prior to the diversification of the clade comprising Staurozoa, Cubozoa, and Scyphozoa.

The title now reads: “Thecate medusozoan polyp from the Upper Ordovician of Québec.”

The abstract now states “…that the species is more closely related to the crown clade including Staurozoa, Cubozoa, Scyphozoa than to other fossil medusozoans, e.g., conulariids and carinachitids.”

In the Systematic paleontology section (page 2), it should state subphylum Medusozoa Petersen, 1979.

The Phylogenetic results section (page 3) now reads “…whereas Paleocanna n. gen. is resolved as a basal crown Medusozoan, nested nearer to the clade containing cubozoans, scyphozoans, and staurozoans”.

On page 4, the last paragraph before the Discussion section now reads “Paleocanna n. gen. nested outside the clade that contains other extinct taxa; this suggests that the genus is part of a lineage of medusozoans, possibly related to conulariids or similar extinct forms. The new medusozoan reflects both morphological and taphonomic diversity within the group. The presence of other extinct medusozoans implies that Paleocanna n. gen. represents a lineage that was relatively diverse in the past.”

The Conclusion section (page 7, second sentence) now reads “As a tubicolous medusozoan that is more closely related to the living medusozoan clade containing Staurozoa, Cubozoa, Scyphozoa, than to the other fossil genera…”

The caption of figure 7 (page 8) now reads: Phylogeny of Cnidaria, with Paleocanna tentaculum n. gen. n. sp. Strict consensus tree generated using 69 ingroup taxa and 236 discrete hard and soft-part morphological characters, polarized using species of the phylum Ctenophora as the sole outgroup. Paleocanna tentaculum n. gen. n. sp. is resolved as an early branching member of the crown group Medusozoa, more closely related to the clade comprising Cubozoa, Scyphozoa, and Staurozoa, than to other fossil medusozoans, e.g., conulariids. Animal silhouettes from PhyloPic (http://phylopic.org/).

These corrections do not affect the results or conclusions of the article. The authors apologize for these errors.