Eventually, she will give you the quest “A Rising Chorus: Act II”, informing you to go to Nessus to complete the Battlefield: Search activity; it is located to the left of the Nessus map.
As you progress through Delve, make absolutely sure to pick up every piece of radiolarian you find, because if you do, you’ll get a ton of extra drops at the end.
After completing the opening section, jumping into the pit and teleporting via the teleporter, move left and smash the first hammer in this battlefield to spawn a ton of radiolarians you want.
Radiolarians take a second, so let them spawn and catch them all. They will be clearly marked on your map.
After completing the next section and falling through the portal under the ground, follow the path until you see an oval opening, you can go down.
If you head to the far left you’ll find the second hammer charge which… you guessed it… spawns a bunch of radiolarians.
Pick it all up and make sure to soak it at the end of the mission – if you’re impatient and just want your loot as quickly as possible – or you can also put him back on the stand where your rewards are increased somewhat, meaning you can get an extra drop or two.
Head towards the ROD to chat with Integrated security and begin your Act 2 quest with this vendor. Failsafe will ask you to collect the “Code Mutations”.