Greek folklore.
Nerite is most commonly found among sailor folklore. He is the only son of Nereus and Doris, and brother to 50 sister (the Nereids). Nerite is an extremely attractive and charming youth, which unfortunately lead to him being turned into a shellfish.

There are two version of how the beautiful Nerite was turned into a shellfish.

In the first, the goddess of love herself, Aphrodyte fell for him. Prior to her ascension to Olympian, she lived in the sea where she became close with Nerite. When it came time for her to go, she asked Nerite to join her in Olympus. The only son of Nereus, wishing to stay with his family, refused.  Not used to rejection, Aphrodite offered him wings if he'd come, but again he declined. So she did what any self-respecting love goddess does when spurned--turned him into a shellfish.

The second version, Nerites has again attracted the affection of a powerful god, but this time it is the God of the sea Posedion, and the love is reciprocated. Nerites became of of Posedion's charioteer and his quickness won the admiration of the sea's creatures.  Unfortuntely, his beauty and athleticism also attracted the attention of Helios (personification of the sun). Helios wanted Nerite to be with him, and when his advances were spurned, turned him into a shellfish