Comparative histology of larval brooding in Thecideoidea (Brachiopoda)

The lecithotrophic larvae of all extant Thecideoidea (Brachiopoda) are brooded within specialised brood pouches. This is the first detailed histological investigation of the morphological structures involved in brooding in the two subfamilies of thecideoid brachiopods, Lacazellinae and Thecidellininae. Comparative descriptions of the brood pouches are presented for two lacazelline species, Lacazella caribbeanensis and Pajaudina atlantica, and two thecidellinine representatives, Minutella sp. and Thecidellina sp. In the highly complex brooding apparatus of female lacazellines, the larvae are attached to two specialised tentacles, which pass through the marsupial notch in the brachial bridge of the dorsal valve and extend into a median brood pouch, which is located in the inner mantle epithelium of the ventral valve. Female thecidellinines lack these structures and brood their larvae in two lateral brood pouches, which are located in cavities surrounded by the brachial lobes of the dorsal valve. Despite the morphological differences, the brood pouches of both Lacazellinae and Thecidellininae are derivatives of the lophophoral epithelium and, thus, are considered to be a homologous structure and synapomorphic character of these thecideoid subgroups.