that looks like it is just the bit that they are supposed to suck in before they leave the egg..helps em survive for a couple days without food...can't remember what it is called..maybe egg yolk? hmmm...well anyway should either get used by the bd or dry up and fall off in the next couple days..one of yemens had that after i had to cut her out of her egg.she is fine now!
very cute by the way! bet they are well lively!?