Fig. 3: Comparative overview of Hox gene complements across major bilaterian lineages.

A schematic phylogeny based on Marlétaz et al.27 illustrates the generalized Hox gene complement for Deuterostomia, Ecdysozoa, Lophotrochozoa, and Rotifera–Acanthocephala, alongside a species-level comparison within Chaetognatha. Boxes to the right of each group or species indicate the presence or undetected status of Hox genes across paralog groups (PG1–PG8 and posterior Hox genes, where applicable). Filled circles indicate identified Hox genes. Diamonds with question marks denote genes not retrieved from transcriptomic data in chaetognath species, though absence cannot be confirmed due to limitations such as low sequencing coverage or stage-specific expression.