ISSN 10623590, Biology Bulletin, 2011, Vol. 38, No. 9, pp. 849–860. © Pleiades Publishing, Inc., 2011. Original Russian Text © E.S. Bocharova, I.A. Kozevich, 2011, published in Zoologicheskii Zhurnal, 2011, No. 11, pp. 1283–1295. 849 INTRODUCTION Peculiarities of reproduction of lower multicellular animals have always been of interest to researchers. Their ability to regenerate, relatively low level of organism integration, and high sensitivity of metabo lism and developmental processes to external factors have resulted in the emergence of unexpected combi nations of sexual and asexual reproduction in the course of their long evolution. The number of studies dealing with certain aspects of reproduction in indi vidual species or groups of lower invertebrates is increasing year by year, providing numerous examples of different variants of sexual and asexual reproduction in these animals. Multivolume collective monographs generalizing available data on reproduction and devel opment of the majority of invertebrate groups were published as long ago as the 1970s and 1990s (for Cni daria, see Campbell, 1974; Fautin, 1992), and new data have been accumulated since then. Sea anemones—solitary hexacorals of the order Actiniaria—are a group of invertebrates showing diverse variants of sexual and asexual reproduction. Like all members of the class Anthozoa, sea anemones have no medusoid generation, and both sexual and asexual reproduction is realized by polyps (Ivanova Kazas, 1975). Sexual reproduction occurs either in an ordinary way (through the maturation of female and male gametes and fertilization) or parthenogenetically (through the development of female gametes without fertilization). During asexual reproduction, a new individual is formed from a fragment or a special out growth of the parent body (IvanovaKazas, 1975). Some species of sea anemones reproduce only sex ually; others, only asexually; but a great number of species combine different mechanisms of both types of reproduction, which replace each other depending on environmental conditions. Stephenson (1929) consid ered that the mode of reproduction varies depending on animal habitat. Combinations of sexual and asexual reproduction have been described, for example, in sea anemones Anthopleura elegantissima (Chia, 1976; Sebens, 1983), Metridium senile (Bucklin, 1979), and Actinia equina (Carter and Thorpe, 1979); partheno genesis is known for the tropical species Cereus pedun culatus (Rossi, 1975). This study is an attempt to summarize available published data on specific features of sexual and asex ual reproduction in sea anemones. This group of invertebrates plays a major role in marine biocenoses, but reviews on their biology are practically absent in the Russian literature. MORPHOLOGY Sea anemones are solitary hexacoral polyps which, in contrast to the majority of colonial forms, have no skeleton. They are diploblastic animals, with the body wall consisting of two cell layers, epidermis and gastro dermis, separated by the extracellular matrix (mesoglea) containing amebocytes (Ruppert et al., 2008). The body is cylinder or truncated cone shaped; its apical end contains the oral disk with a fringe of tentacles arranged in one or several concen tric circles around the mouth opening (Figs. 1a, 1b). Sea anemones of the genus Limnactinia have no tenta cles. The basal body end in the majority of animals is extended into the basal (pedal) disk, which serves for attachment to the substrate (Fig. 1a). Wormlike sea anemones (e.g., of the family Edwardsiidae) have no pedal disk, but their basal body end forms a swelling (physa) for anchoring in ground (Fig. 1b). Modes of Reproduction in Sea Anemones (Cnidaria, Anthozoa) E. S. Bocharova a, b and I. A. Kozevich a a Faculty of Biology, Moscow State University, Moscow, 119991 Russia email: ekaterinabocharova@yandex.ru b Russian Federal Research Institute of Fisheries and Oceanology, Moscow, 107140 Russia Received June 1, 2010 Abstract—The data on different modes of reproduction in sea anemones are generalized. These animals can reproduce sexually in an ordinary way or by parthenogenesis. Asexual reproduction occurs in various forms, such as transverse and longitudinal fission, pedal laceration, or autotomy of tentacles. Specific features of dif ferent variants of sexual and asexual reproduction and their combinations in sea anemones from different habitats of the World Ocean are discussed. Keywords: Cnidaria, sea anemones, sexual reproduction, parthenogenesis, asexual reproduction. DOI: 10.1134/S1062359011090020