ИСТИНА

Presence of the metamery in many representatives from three main stems of Bilateria allowed researchers to suggest the presence of metamery in the last common bilaterian ancestor. Adult brachiopods seem to be lack metamery. However, the metamery is described in larvae of craniid brachiopod Novocrania anomala, which have three pairs of setae bundles that are repetitively arranged along anterior-posterior axis, unpaired anterior coelom, and three pairs of coelomic sacs. Here, we describe for the first time the metamery in larvae of articulate brachiopod Coptothyris grayi, which have three pairs of coelomic sacs arranged along the anterio-posterior axis on the both sides of the archenteron. Metamery was also suggested in adult brachiopods. According to some opinions, the body plan of brachiopods originated due to the folding of the worm-like ancestor on the ventral side. In adult brachiopods, the trunk coelom contains two lateral mesenteries that extend at angle in respect to each other and to anterior-posterior axis. If the anterior-posterior axis of brachiopods is curved, then the lateral mesenteries are located like dissepiments between segments. Each lateral mesentery supports a pair of nephridial funnels and this fact may confirm that lateral mesenteries of brachiopods are true dissepiments. Thus, the brachiopods have preoral and lophophore coeloms and also three trunk segments. These data let us hypothesize that the ancestor of brachiopods was a metameric animal. The segments of brachiopods was possibly reduced due to the extremely shortening of anterior-posterior axis after folding of a brachiopod ancestor.