MYRTOESSA was the Naiad Nymph of a well in the town of Megalopolis in Arkadia (southern Greece).
MYRTOESSA (Murtôessa), the nymph of a well of the same name in Arcadia; she was represented at Megalopolis along with Archiroe, Hagno, Anthracia and Nais. (Paus. viii. 31. § 2.)
Source: Dictionary of Greek and Roman Biography and Mythology.
Pausanias, Description of Greece 8. 31. 4 (trans. Jones) (Greek travelogue C2nd A.D.) :
"[At Megalopolis in the enclosure of Demeter and Persephone:] The table also has a representation of Nymphai, Neda carrying the infant Zeus and another Arkadian Nymphe Anthrakia holding a torch, and Hagno with a water-jar in one hand and a drinking cup in the other; Ankhiroe and Myrtoessa are carrying water-jars and in fact water is pouring down from them."
- Pausanias, Guide to Greece - Greek Geography C2nd AD