How do lamp shells reproduce?

The reproduction of lamp shells (brachiopods) is not fully understood, but it is known that in most genera, the sexes are separate.1

During the reproductive process, eggs and sperm are discharged into the mantle cavity through funnel-shaped excretory organs called nephridia, which are located on each side of the mouth. Fertilization typically occurs externally in the water.1

In a few specific genera, the young develop internally within brood pouches formed by a fold of the mantle, which is a soft extension of the body wall. Following fertilization, the egg develops into a free-swimming larva that eventually settles on the ocean floor to mature. The duration of this free-swimming stage varies significantly depending on the type of brachiopod: it lasts only a few days for articulate species, while inarticulate species may remain in the larval stage for a month or up to six weeks.1