 If they contact another sponge of the same species, the water flow carries them to choanocytes that engulf them but, instead of digesting them, metamorphose to an ameboid form and carry the sperm through the mesohyl to eggs, which in most cases engulf the carrier and its cargo.A few species release fertilized eggs into the water, but most retain the eggs until they hatch.There are four types of larvae, but all are balls of cells with an outer layer of cells whose flagellae or cilia enable the larvae to move.