Temereva E.N., Malakhov V.V. 2006. [The answer to Thomas Bartolomaeus: “Larva of phoronid Phoronopsis harmeri Pixell, 1912 has trimeric coelom organization”] // Invertebrate Zoology. Vol.3. No.1: 1–21 [in Russian, with English summary].

Department of Invertebrate Zoology, Moscow State University, Vorobjevy Gory, Moscow, 119992, Russia. E-mail: temereva@mail.ru

KEY WOrDS: Archicoelomate conception, Phoronida, larvae, coelomic system.

ABSTRACT: Traditionally phoronids are considered as achricoelomate animals, because phoronid larvae and adult have trimeric coelom organization. Recent investigations of Dr. Bartolomaeus revealed that phoronids larvae have only one coelom, namely metacoel, and therefore phoronids can not be considered as archicoelomate organisms. Microscopical anatomy and ultrastructure of Phoronopsis harmeri larva coelomic system were investigated by methods of histology and electron microscopy. Larva has three parts of coelom such as protocoel, mesocoel, metacoel. The first has cylindrical shape and lies in the preoral lobe under aboral organ. The second is horseshoe-shaped which is open on the dorsal side and lies in the basis of tentacular ring. Coelomic canals go away from mesocoel horseshoe to each tentacle. Metacoel lies in the hyposphere from tentacular ring to telotroch and has shape of cylinder which gathers round the digestive tract. Metacoel divides into right and left parts by ventral mesentery. Lining of protocoel is formed by monociliary epithelial cells which connected by apical adherens junctions and ECM (extracellular matrix) lying under these cells. Thus protocoel lining reperesents true epithelium. Mesocoel lining consists of monociliary myoepithelial cells lying on ECM of ectodermal epithelium and forming wall of tentacular blood vessels in each tentacle. Monociliary myoepithelial cells form metacoel lining. Data of this work reveal that phoronids larvae of Phoronopsis genera do have trimeric organization of coelom. Trimeric organization is original state of phoronid larvae coelomic system.

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