Opis, Oupis or Upis, a Hyperborean nymph, daughter of the North Wind Boreas.[5] Together with Arge, she carried an offering which had been vowed for the birth of Apollo and Artemis, to Eileithyia, at Delos.[6] Later on, Opis, along with her sisters Hecaerge (Arge) and Loxo, became the handmaidens of the goddess.[7]Orion tried to rape her but the giant was shot by Artemis.[8] In later myths, Opis was called by the goddess Diana (Artemis) to avenge the death of the Amazon-like female warrior Camilla. Diana gave Opis magical weapons for revenge on Camilla's killer, the EtruscanArruns. Opis saw and lamented Camilla's death, and slayed Arruns with an arrow in revenge as directed by Diana.[9][10]
Upis, the name of a mythical being said to have reared Artemis.[11] She may be the same to above nymph.
^This was definitely a misinterpretation of Hyginus in Virgil's Georgics4.343 which suggests that Opis was a naiad, more likely an Oceanid, rather than a Nereid.