hypogiemnia, and where the ie came from
heard as hypogiemnia
spelled hypogymnia
From English spelling habits. The name is hypogymnia.
What the ear did
Writing ie for a short i is common enough in English, but nothing in Greek supports it here. The syllable is gym, as in gymnasium, and it is spelled that way.
H-Y-P-O-G-Y-M-N-I-A
The full entry for hypogymnia covers the name itself.