Why are gemma cups and gemmules differ from each other?

Gemmae cup is a specialized structure on the gametophyte of certain liverworts that produces asexual plantlets (gemmae) capable of starting new gametophytes. Gemmules on the other hand is a resistant, overwintering capsule formed by freshwater and marine sponges that contains masses of mesenchyme cells (the amoeboid mesenchyme cells are released and organize themselves into a sponge)