Reproductive biology

The onset of breeding and the length of the spawning season depend primarily on water temperature, together with latitudinal and seasonal effects. In temperate waters, the breeding period takes place in midsummer and lasts about a month and a half; in the tropics, however, breeding may take place throughout the year.

Inarticulated brachiopods are dioecious. The sex ratio, at least in lingulides, is one to one. There is a single continuous gonad mass on each side of the visceral cavity in lingulides. Discinids have two gonads in the posterior part of the visceral cavity; males sometimes possess an additional single U-shaped testis. In the craniids, the gonads are in six separate groups, two in the visceral cavity and two in each lobe of the mantle. Fertilization is external in the lingulides, with synchronization of spawning in the two sexes. Ova and sperm are discharged through the metanephridia (primitive excretory organs) acting as gonoducts into the current of water that leaves through the lophophore. The occurence of fertilization is unknown in the discinids and craniids.

The larvae in lingulides and discinids have two parts: the lobe at the upper end or apex, which will form the future body; and the mantle lobe, which will develop into the future mantle lobes. The pedicle arises from the ventral mantle lobe during the larva's long planktotrophic stage. The larva grows in size and complexity as it feeds on phytoplankton. The duration of this stage ranges from 3-6 weeks. The lecithotrophic larva of Neocrania has a short larval stage of about 4-6 days after fertilization.

There is no true metamorphosis in the inarticulated bra-chiopods. The larval organs either atrophy (wither away) or are detached after the animal settles on the substrate.

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