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 

Greek Myth.
​Ascalabus son of Misme (also known as Abas son of Metaneira) was changed by the Greek goddess Demeter into a lizard. 

While searching for her daughter Persephone in Attica, Demeter came to the small thatched roof cottage of an old peasant woman named Misme. Misme offered the goddess a sweet barley drink of barley (pennyroyal and barley groats), and Demeter accepted.

It was all going well until Misme's son Ascalabus mocked the goddess for drinking so much, so quick. He laughed at her and ordered for a cask to be brought up.   In response to his rudeness, Demeter threw what remained of her drink in his face and turned the boy into a lizard.

Sources:
Antoninus Liberalis (2  CE) Metamorphoses, Greek
Ovid (1 BCE - 1 CE) Metamorphoses, Latin/Roman

​Roman Folklore.
From Virgil's The Aeneid, Achates was the best friend of the Trojan Hero Aeneas.
​Achates is renown for his loyalty and being a faithful companion.

​Acestes was the son of a Trojan woman Egesta, and a Sicilian river deity named Crimisus. 

When the Trojans refused to pay thanks to Poseidon and Apollo, whom helped them with their wall. The gods punished Troy by sending monsters to infest the city and devour it's citizens.

​Egesta's father feared for his daughter's safety. He sent her to Sicily where she met the river god Crimisus and conceived the hero Acestes.

In Virgil's epic, The Aeneid, Jupiter shows favour to Acestes during a a trial of skill by setting aflame the arrow Acestes had shot.

Acestes went on to become one of the founders the Sicilian city of Segesta.

Greek Mythology.
Absyrtus was a Colchian prince (modern day Georgia), grandson of Helios (sun god), and a younger brother of Medea--a sorceress who married the Greek hero Jason. 

Apsyrtus had golden armour and a golden shield that reflected the sun's rays. To look upon him in his gear could cause eye pain. His weapon was a quivering spear and he drove the golden cart of his grandfather Helios. During the brother's war (between his father and uncle) he fought bravely on the frontline. 

He was murdered by his own sister, Medea in the town of Tomi (Romania). In order to escape her father, Medea killed Absyrtus, sliced him up and scattered his pieces on the road. She'd hoped this would slow down her father, as he'd need to collect all the parts of his son in order to give a proper burial.