Embryonic development of the Mediterranean starfish <i>Hacelia attenuata</i>

Abstract Starfish play essential ecological roles as predators and ecosystem regulators, however detailed developmental descriptions exist for only a handful of species, none of which come from the Mediterranean. In this study we provide the first full account of the development of the Mediterranean starfish Hacelia attenuata , from oocyte maturation through embryogenesis and larval formation, showing that its development largely follows the canonical pattern known from other asteroids. Oocytes resume meiosis when exposed to 1-methyladenine, exhibiting conserved features such as formation of a nuclear actin shell for chromosome gathering prior to meiotic spindle assembly. Embryogenesis then proceeds through equal radial cleavages to form a ciliated blastula, followed by gastrulation via invagination and mesenchymal cell delamination. The larvae develop through typical bipinnaria and brachiolaria stages, displaying characteristic feeding structures and attachment organs. Importantly, developmental rate increases substantially at higher temperatures, consistent with the species distribution in warm Mediterranean waters. Together, these findings position H. attenuata as a promising new model for studying thermal adaptation, environmental resilience and conserved developmental mechanisms in starfish.