As adjectives the difference between aplacental and placental
is that aplacental is lacking a placenta; belonging to the aplacentata while placental is of or pertaining to the placenta, or to the placentalia.
As a noun placental is
any animal that is a member of the placentalia.
placental
English
Adjective
(-)
Of or pertaining to the placenta, or to the Placentalia
Having a placenta
Noun
(
en noun)
Any animal that is a member of the Placentalia