Final answer:
Josquin's Ave Maria . . . virgo serena is a polyphonic and a cappella motet.
Step-by-step explanation:
The main features of Josquin's Ave Maria . . . virgo serena are that it is polyphonic and a cappella. A polyphonic texture means that there are multiple independent melodic lines being sung at the same time. The fact that the piece is a cappella means that it is performed without any instrumental accompaniment.