ИСТИНА

We suppose the brachiopod ancestor to have a pelago-benthic life cycle including planktotrophic shell-free larva, which had prominent ciliary bands. At settlement, the larva folded ventrally and the secretion of shell started. A few life cycle patterns evolved from this base ancestral type. 1. The life cycle of the recent craniids closely resembles the ancestral life cycle, but differs in the lecithotrophy of primary shell-free larva. At settlement, it folds ventrally and forms a shell. 2. Another way of the life cycle evolution is a prolongation of the pelagic stage by transformation of folding stage into the secondary larva. The last was already folded but still wasn't shelled. The folded larva was putatively planktotrophic and had long setae to facilitate a buoyancy. 3. The folded larva with two pairs of setae exists in the life cycle of recent articulate brachiopods but it is totally lecitotrophic. 4. In the recent discinids, the primary planktotrophic larva reduces, but the life cycle is prolongated by two secondary larvae. The first one is folded larva lacking the shell but having the larval setae. It is possibly planktotrophic because of having fully developed mouth and anus. The second one is the shelled swimming juveniles. 5. The life cycle of the recent lingulid includes only one swimming stage - planktotrophic juveniles with shell. All preceding stages are compressed within the embryogenesis and hidden under the egg membrane.