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Lyra: originally called Chelys, because of the tortoise shell used as its sound box. According to Nicomachus of Gerasa (Ist cent. AD), the tortoise-shell Lyra was invented by god Hermes, who gave it to Orpheus. "Orpheus taught Thamyris and Linos, and Linos taught Hercules. When Orpheus was killed by the Thracian women, his lyra was thrown into the sea, and washed ashore at Antissa, a city of Lesbos, where it was found by fishermen, who brought it to Terpander, who in turn carried it to Egypt and presented it to the Egyptian priests as his own creation."

 We don't know how many strings the original Lyras had. By the time of Terpander (8th-7th cent. BC) Lyra was a seven stringed instrument and from many ancient sources we know that this type remained in use for a long time during the classical period. The addition of an eighth string in the 6th century BC is credited by Nicomachus of Gerasa to Pythagoras. By the fifth century there were Lyras with anything from 9 to 12 strings. The strings (neura) were made of animal gut of sinew, but there are also references of strings made of linen or hemp. 
Lyra was mainly used for the musical education of the young, and by amateur players in general.

Cithara   plucked instrument with 5 strings originally, but  later with as many as 12 strings. Cithara was bigger than the Lyra and it was the principal concert instrument  played by professional musicians, the citharodes.  According to Plutarch, cithara was designed by Cepion, a student of Terpander. Many instrument names like guitar, cittern, zither etc. derive from the word cithara.

Barbitos or Barbiton is an instrument of the Lyra family and resembles a Lyra, but it has longer arms and narrower sound box. Musicians of the School of Lesbos, like Alcaeus and Sappho, are frequently depicted in vases playing the Barbitos.

Phorminx  probably the oldest of the Cithara type instruments. From references in ancient sources (Homer, Hesiod, Aristophanes) we know that Phorminx was richly decorated  with gold and ivory, and  accompanied  the singing of the epic singers called rhapsodes.

Epigonion belongs to the psaltery family and it is the instrument with the largest number of strings, sometimes as many as forty (Polydeuces). It may owe its name to the fact that it was played 'on the knee' - Greek 'epi gonu', or maybe because its inventor was someone named Epigonus.

Pandouris or pandourion, also called trichord because it had three strings, is
the first fretted instrument known, forerunner of the various families of lutes worldwide.
Source of our knowledge about this instrument is the Mantineia marble (4th cent BC, now exhibited at Athens Archaeological Museum) depicting the mythical contest between Apollo and Marsyas, where Pandouris is being played by a muse seated on a rock.