Thomas Keightley (The Mythology of Ancient Greece and Italy) says the seven nymphs nurtured Dionysus, and accompanied Artemis as maidens until the giant Orion saw them and wished to pursue them. Zeus transformed them into pigeons before turning them into the stars.
Thomas Keightley says of the seven sisters:
"The Pleiades were said to be seven in number, the daughters of Atlas and the Oceanis Pleione. Their names were Maia, Electra, Taygete (the mothers by Zeus of Hermes, Dardanos and Lacedaemon), Halcyone and Celaeno (who bore to Poseiddn Hyrieus the father of Orion and Lycos), Sterope (the mother of CEnomaos by Ares), and Merope, who married Sisyphos."
The Mythology of Ancient Greece and Italy, by Thomas Keightley