Horseshoe crab

The horseshoe crab is a sea creature you catch while swimming in the sea (dive where you see bubbles). Look for a medium shadow. In the northern hemisphere look for it in Jul – Sep, from 9 PM – 4 AM. It can only appear after you have caught 20 sea creatures. Nook's Cranny pays 2,500 Bells.

A Medium shadow that only appears from 9pm to 4am, after 20 catches. It moves at a moderate pace and sells for 2,500 Bells, so late swims pay off.