Final answer:
The theme that connects all the stories told between Achelous and Theseus' crew in Ovid's Metamorphoses is the theme of transformation or metamorphosis.
Step-by-step explanation:
The theme that connects all the stories told between Achelous and Theseus' crew in Ovid's Metamorphoses is the theme of transformation or metamorphosis. Throughout these stories, characters undergo various physical and emotional transformations, reflecting Ovid's exploration of change and the fluidity of identity. For example, in the story of Achelous, the river god transforms into different forms to compete for Deianira's hand in marriage. In the story of Theseus' crew, they encounter numerous transformations, such as the transformation of the pirates into dolphins by Dionysus.