Hi Barbara,

Actually, superfamily names end in -oidea
It is family names that end in -idae
and subfamily names in -inae
The family ending itself always has a single "i" -idae
A double "i" (iidae) is the result of adding the standard -idae ending
onto a noun root that ends in "i".
The majority of such roots do not end in "i"
VOLUT-
OLIV-
ARCHITECTONIC-
CON-
VENER-
PECTIN-
So the family name becomes Volut-idae; Oliv-idae; Architectonic-idae; etc.
But when the root itself ends in "i"
CERITHI-
TRIVI-
LOTTI-
MOPALI-
Then adding the standard -idae ending yields:
Cerithi-idae; Trivi-idae; Lotti-idae; Mopali-idae

Paul M.