User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-124.148.221.67-20120923231513/@comment-5020152-20120924002435

My theory is that the "Immature Sponge" is the name that hunters came up with when they compared it to the "mature" sponge of a Royal Ludroth. The females are full-grown, but their sponges are not and will never develop.