ISSN 10630740, Russian Journal of Marine Biology, 2010, Vol. 36, No. 2, pp. 109–116. © Pleiades Publishing, Ltd., 2010. Original Russian Text © E.N. Temereva, V.V. Malakhov, 2010, published in Biologiya Morya. 109 1 Phoronids constitute a small (in terms of species number) phylum of invertebrate animals, the Phoron ida. Adult phoronids have a sessile mode of life; they are tube dwellers and live within the thickness of solid substrates or in soft grounds. Only the anterior part of the body protrudes from the tubes; it bears the lopho phore, a food capturing apparatus consisting of cili ated tentacles. The lophophore of phoronids performs different functions: gas exchange occurs through the thin tentacular integument, tentacles bear mechan oreceptor cells, in some phoronids the eggs are incu bated in the lophophore, etc. However, the major function of the lophophore is a trophic one; it carries out water filtration and extraction of food particles [7, 8, 10]. In phoronids this process is still poorly studied and many important aspects still remain uncertain. To date, it has been revealed that phoronids belong to organisms with an socalled upstream filtration pat tern; i.e., water flow enters lophophore from above, reaches the space between the distal extremities of the outer and inner rows of tentacles and is discharged through gaps between the lateral margins of the tenta cles [11, 16–20, 22]. However, the available literature provides no information about the dietary range of 1 The article was translated by the author. phoronids, it is not known what they eat and how the selection between edible and inedible particles occurs. The target of this project was a morpho–functional analysis of lophophore structure in phoronids, using Phoronopsis harmeri Pixel, 1912 and the understand ing of filtration mechanisms. MATERIALS AND METHODS As the materials for this project we used adult spec imens of Phoronopsis harmeri collected in Vostok Bay of the Sea of Japan, around the Vostok Marine Biolog ical Station (Institute of Marine Biology FEB RAS) in August–September of 1996–1998. The animals were removed from tubes, fixed in a 4% formalin solution in filtered seawater, rinsed from the fixative in distilled water and stored in 70% ethanol. The heads with the lophophores were then treated in an ascending ethanol series, butanol, xylene, and paraplast. Finally, the samples were embedded into paraplast and cut into 5 μm sections with a Leica RM 2125 rotational micro tome. The sections were stained with Caracci hema toxylin and embedded into Canada balsam. Alto gether two sagittal series, two frontal series and seven transverse series were prepared. The sections were examined under a Zeiss AxioPLAN2 light microscope INVERTEBRATE ZOOLOGY Filter Feeding Mechanism in the Phoronid Phoronopsis harmeri (Phoronida, Lophophorata) 1 E. N. Temereva and V. V. Malakhov Moscow State University, Moscow, 119991 Russia email: temereva@mail.ru Received September 15, 2009 Abstract—Phoronids, like other Lophophorata (Bryozoa and Brachiopoda) are filter feeders. The lopho phore performs various functions, the most important of which is the collection and sorting of food particles. The mechanism of sorting has been well studied for many other groups of invertebrate, but until now it has remained obscure for phoronids. With the help of functional morphology data we are proposing a possible scheme of sorting in phoronids on the example of Phoronopsis harmeri. The lower limit of the particle size is defined by the distance between laterofrontal cilia of tentacles and equals 1.2 μm. Larger particles are trans ferred by frontal cilia to the basis of the tentacles, where they pass into the lophophoral groove. The distance between the epistome and the external row of tentacles regulates the upper limit of the particle size that are suitable for food. Only particles whose size does not exceed 12 μm get into the lophophoral groove and further into the mouth. Larger particles collect in the space above the epistome and are removed from the lopho phore. The size of the food particles that phoronids consume by filtration lies in a range 1.2–12 μm. These are bacteria and small phytoplankton organisms. At the same time the significant individual mobility of the phoronid tentacles plays an important role in the expansion of the pabular spectrum to large inactive zoop lankton and phytoplankton organisms reaching a size of 50–100 μm. Key words: Phoronids, sorting, lophophore, filter feeder, Phoronopsis harmeri. DOI: 10.1134/S1063074010020057