Jigoku Sensei Nube: Kyoufu no Natsu Yasumi! Asashi no Uni no Gensetsu

When Nube and his class arrive at a small island to carry out beach activities, they heard a foreboding tale from an old man residing on the island. Legend has it that there is a creature known as the sea spider in the open seas around the island. When the creature is past 200 years old, it will turn into a monster and devour humans to satisfy its appetite. However, curiosity kills the cat and Yukime decides to pursue the authenticity of the legend. (imdb)