This two-part episode was later released as a TV movie titled Destination Moonbase-Alpha (1978), which had the year changed from 1999 to 2100.
In a deleted scene (right in between Helena's line "He taught me everything there is to know about being a doctor" and Maya's line "What do you do, Guido?"), it was revealed (during a discussion with Dr. Shaw) that while still in medical school, Helena attempted to save her dying father but was unsuccessful.
Stuart Damon (Guido) played the Eagle pilot Parks in the Season One episode Matter of Life and Death (1975).
David Jackson (alien voice) had played "Alien Strong" (and also provided the voice of the Judges) on The Rules of Luton (1976).
In the episode's novelization by Michael Butterworth, the creatures seen here are "cells" of the large swirling space entity the Alphans had encountered in The Lambda Factor (1976).