Reparations Story Notes:

The Ethereal government is the Advent Federation.  This is a multi-world federation made of the races 'visited' by the Temple Ship in the past, whom the Ethereals have helped to 'heal'.  While vaguely sinister, they do not view the Ethereals as Gods, but rather alien benefactors.
Members include:
Sylthen (thin men/snakewomen)  Homeworld:  Nerveen
Muton  Homeworld:  Ophabos
Sectoid  Homeworld:  Secta
Iilvan (synthetic race which served as the basis for Sectopods)  Homeworld:  None
It should be noted that the Floaters were mutilated Mutons.

Chryssalids are native to a planet called Moltova, which has been referred to as 'giant crab Australia,' or 'Krogan vacation spot.'
Chryssalids come in several varieties, from ones large enough to ride into battle (Chryssalid Spartikus), ones the size of the now-extinct terran polar bear (Chryssalid Krogus), and the much more common Chryssalid Domesticus, which varries in size much like dog breeds and have become designer pets amongst much of the Citadel.