Marine gymnolaemate bryozoans are indirect developers showing a great variation with regard to their reproductive patterns, developmental modes and larval forms. Few species are free-spawning and have planktotrophic larvae (cyphonautes) with functional gut and bivalve shell. Others incubate endotrophic larvae (lecithotrophic, matrotrophic or of combined type) with rudimentary gut (pseudocyphonautes) or without gut at all (coronate larva).
The comparative study of various larval types from both close-related and distant gymnolaemata clades helps us understand the major trends in the evolution of ontogenesis within this group. Special attention is given to the presence of embryonic brooding and early developmental stages (cleavage and gastrulation) as well as larval anatomy and type of larval nutrition (planktotrophy vs endotrophy). Apart from presence and functionality of the gut, the most significant larval feature is presumptive juvenile rudiments in the form of blastemic cells. Gymnolaemate larvae show several variants of their location and their fate varies in species from different families. Taking into account the independent origins of non-feeding larvae among Gymnolaemata, we can propose several scenarios of their evolution from planktotrophic ancestral form using morphological series obtained during our study.