(A) Simplified phylogenetic tree of metazoans showing placement of Hofstenia within xenacoelomorphs (red line). Dashed black line indicates the alternative position of xenacoelomorphs, as sister group to ambulacrarians (e.g., sea stars); (Philippe et al., 2019; Kapli and Telford, 2020; Kapli et al., 2021). (B) Life cycle of Hofstenia miamia in lab conditions. (C) An adult worm schematic drawing showing major structures: m, mouth; nr, neural condensation (Hulett, Potter and Srivastava, 2020); ph, pharynx; cp, central parenchyma; ep, epidermis. (D) Hofstenia embryos are amenable to microinjections. Left, live embryos at 2-cell and zygote stages; right, injection of fluorescent dextran into a zygote. Scale bars, 200 μm. (E) Translation of foreign mRNAs. Left, detection of nuclear-localized H2B-RFP and membrane-bound GFP (mGFP), 1.5 days after single blastomere injection of a 2-cell stage embryo; right, single cell photoconversion of Kaede (white arrowhead), 2 days after injection of Kaede mRNA into a zygote. Scale bars, 100 μm.