In Greek mythology, Arethusa (Ancient Greek Ἀρέθουσα) is one of the Hesperides who tend Hera's golden apples beside Ladon. Apollodorus names her fourth with Aegle, Erythia, and Hesperia. Distinct from the Sicilian spring-nymph pursued by Alpheus (`arethusa-nymph`) and from Homeric or Nereid Arethusas.
Adapted from Wikipedia, "Arethusa (mythology)" and "Hesperides" · CC BY-SA 4.0
I.Among the apple-guardians
Apollodorus (Bibliotheca 2.5.11) lists four Hesperides at Ladon's watch: Aegle, Erythia, Hesperia, and Arethusa. They keep the golden fruit Earth gave Hera — the western labour of Heracles. Apollonius' Argonautica episode after Ladon's death names only Aegle, Erytheis, and Hespere; Arethusa is absent from that three-name roll but remains in Apollodorus' quartet.
Parentage of the whole brood (Nyx, Atlas, Phorcys, and other claims) stays on the collective hesperides node under topic hesperides-parentage.
II.Homonym care
The atlas id arethusa-hesperid with kinds hesperid is Apollodorus' western evening sister alone. Distinct from arethusa-nymph (Ovid's Sicilian spring fleeing Alpheus), from Homer's spring on Ithaca, and from Nereid Arethusa in some catalogues.