We compared the ultrastructure of spermatozoa from the bivalves Anomalocardia brasiliana and Tivela mactroides (Veneridae). The spermatozoa of both species were of the ectaquasperm type in which the head contains a curved nucleus with a short cone-shaped acrosome. An invagination penetrated almost the entire length of the acrosome. The midpiece contained a pair of orthogonally arranged centrioles surrounded by spherical mitochondria and the flagellum had the typical 9 + 2 structure The spermatozoa of A. brasiliana had a slightly curved nucleus while those of T. mactroides had a long, prominently curved nucleus. The mitochondria were equally distributed around die centrioles in the midpiece of A. brasiliana spermatozoa, but asymmetrically in the midpiece of T. mactroides spermatozoa. There were six mitochondria and glycogen clusters in the middle piece of the T. mactroides spermatozoon. The presence of glycogen clusters and die higher number of mitochondria, in comparison with Anomalocardia brasiliana, could extend the longevity of the Tivela mactroides spermatozoa. An increase in sperm life expectancy implies in an increase in the probability of finding eggs and accomplishing fertilization. The glycogen clusters and the higher mitochondria number possibly correspond to an adaptive advantage to the bivalves in turbulent waters.1234293302Amaral, C., Arruda, E.P., Rizzo, A.E., (2005) Manual de Identificação Dos Invertebrados Marinhos da Região Sudeste-Sul Do Brasil., 1, p. 288. , Universidade de São Paulo Press, São PauloAnderson, W.A., Personne, P., The localization of glycogen in the spermatozoa of various invertebrate and vertebrate species (1970) The Journal of Cell Biology, 44, pp. 29-51Anderson, W.A., Personne, P., Molluscan spermatozoon - Dynamic aspects of its structure and function (1976) American Zoologist, 16, pp. 293-313Arruda, E.P., Amaral, C.Z., Spatial distribution of mollusks in the intertidal zone of sheltered beaches in southeastern of Brazil (2003) Revista Brasileira de Zoologia, 20, pp. 291-300Arruda, E.P., Domaneschi, O., Amaral, C.Z., Mollusk feeding guilds on sandy beaches in São Paulo State, Brazil (2003) Marine Biology, 143, pp. 691-701Bernard, R.T.F., Hodgson, A.N., The fine structure of the sperm and spermatid differentiation in the brown mussel Perna perna (1985) South African Journal of Zoology, 20, pp. 5-9Eckelbarger, K.J., Bieler, R., Mikkelsen, P.M., Ultrastructure of sperm development and mature sperm morphology in three species of commensal bivalves (Mollusca: Galeommatoidea) (1990) Journal of Morphology, 205, pp. 63-75Erkan, M., Sousa, M., Fine structural study of the spermatogenic cycle in Pitar rudis and Chamelca gallina (Mollusca, Bivalvia, Veneridae) (2002) Tissue & Cell, 34, pp. 262-272Etchevers, S.L., Notas ecológicas y cuantificación de la población de guacuco (1976) Tivela Mactroides, 15, pp. 57-64. , (Born, 1778) (Bivalvia-Veneridae), en la ensenada de La Guardia, Isla de Margarita, Venezuela. Boletin del Instituto Oceanografico de la Universidad de OrienteFranzén, A., Comparative morphological investigations into the spermiogenesis among Mollusca (1955) Zoologische Bijdragen Uppsala, 30, pp. 399-456Franzén, A., On spermiogenesis, morphology of the spermatozoon, and biology of fertilization among invertebrates (1956) Zoologische Bijdragen Uppsala, 31, pp. 355-482Franzén, A., Sperm structure with regard to fertilization biology and phylogenetics (1977) Verhandlungen der Deutschen Zoologischen Gesellschaft, pp. 123-138Franzén, A., Ultrastructural studies of spermatozoa in three bivalve species with notes on evolution of elongated sperm nucleus in primitive spermatozoa (1983) Gamete Research, 7, pp. 199-214Garrido, O., Gallardo, C.S., Ultrastnicture of sperms in bivalve mollusks of the Mytilidae family (1996) Invertebrate Reproduction & Development, 29, pp. 95-102Gharagozlou, I.D., Pochon-Masson, J., Etude comparative infrastructurale du spermatozoide chez les palourdes de France (1971) Archives de Zoologie Experimentale et Generale, 112, pp. 805-817Guerra, R., Campos, B., Esponda, P., Analysis of the spermatozoa of four bivalves with particular reference to the acrosome and plasma membrane glycoproteins (1994) J.SUBMICROSC.CYTOL.PATHOL., 26 (4), pp. 489-495Guerra, R., Sousa, M., Torres, A., Oliveira, E., Baldaia, L., Fine structure of acrosome biogenesis and of mature sperm in the bivalve mollusks Glycymeris sp. (Pteriomorphia) and Eurhomalea rufa (Heterodonta) (2003) Helgoland Marine Research, 57, pp. 7-12Gwo, J.C., Yang, W.T., Sheu, Y.T., Cheng, H.Y., Spermotozoan morphology of four species of bivalve (Heterodonta, Veneridae) from Taiwan (2002) Tissue & Cell, 34, pp. 39-43Healy, J.M., Sperm ultrastructure in the marine bivalve families Carditidae and Crassatellidae and its bearing on unification of the Crassatelloidea with the Carditoidea (1995) Zoologica Scripta, 24, pp. 21-28Healy, J.M., Comparative spermatozoal ultrastructure and its taxonomie and phylogenetic significance in the bivalve order Veneroida (1995) Advances in Spermatozoal Phylogeny and Taxonomy., 166, pp. 155-166. , Jamieson, B.CM., J. Ausio, and J.-L. JUSTINE (eds.) Mémoires du Museum National d' Histoire NaturelleHealy, J.M., Buckland-Nicks, J.A., Jamieson, B.G.M., Spermatozoal ultrastructure of spiny oysters (Spondylidae, Bivalvia) including a comparison with other bivalves (2001) Invertebrate Reproduction & Development, 40, pp. 27-37Healy, J.M., Mikkelsen, P.M., Bieler, R., Sperm ultrastructure in Glauconome plankta and its relevance to the affinities of the Glauconomidae (Bivalvia: Heterodonta) (2006) Invertebrate Reproduction & Development, 49, pp. 29-39Hodgson, A.N., Bernard, R.T.F., Van Der Horst, G., Comparative spermatology of three species of Donax (Bivalvia) from South Africa (1990) Journal of Molluscan Studies, 56, pp. 257-265Introíni, G.O., Magalhães, C.A., Aguiar Jr., O., Quaresma, A.J.C., Lino-Neto, J., Recco-Pimentel, S.M., Spermatozoan morphology of Brachidontes dancinianus and B. solisianus (Bivalvia, Mytilidae) from the southern Brazilian coast (2004) Invertebrate Reproduction & Development, 46, pp. 149-158Intróini, G.O., Magalhães, C.A., Fortunato, H., Reccopimentel, S.M., Comparison of the spermatozoan morphology of Isognomon bicolor and Isognomon alatus (Mollusca, Bivalvia, Isognomonidae) (2009) Tissue & Cell, 41, pp. 67-74Johnson, M.J., Casse, N., Le Pennec, M., Spermatogenesis in the endosymbiont-bearing bivalve Loripes lucinalis (Veneroida: Lucinidae) (1996) Molecular Reproduction & Development, 45, pp. 476-484Komaru, A., Konishi, K., Ultrastructure of biflagellate spermatozoa in the freshwater clam, Corhicula leana (Prime) (1996) Invertebrate Reproduction & Development, 29, pp. 193-197Matos, E., Matos, P., Casal, G., Azevedo, C., Ultraestnitura do espermatozóide de Protothaca pectorina (Lamark) (Mollusca, Bivalvia) do litoral norte do Brasil (1997) Revista Brasileira de Zoologia, 14, pp. 779-783Mclachlan, A., Dugan, J.E., Defeo, O., Ansell, A.D., Hubbard, D.M., Jaramillo, E., Penchaszadeh, P.E., Beach clam fisheries (1996) Oceanography and Marine Biology: An Annual Review, 34, pp. 163-232Narchi, W., Comparative study of the functional morphology of Anomalocardia brasiliana (Gmelin, 1791) and Tivela mactroides (1972) Bulletin of Marine Science, 22, pp. 643-670. , (Born, 1778) (Bivalvia, Veneridae)Nicotra, A., Zappata, S., Ultrastructure of the mature sperm and spermiogenesis in Callista chione (Mollusca, Bivalvia) (1991) Invertebrate Reproduction & Development, 20, pp. 213-218Park, C.K., Park, J.J., Lee, J.Y., Lee, J.S., Spermatogenesis and sperm ultrastructure of the equilateral venus Gomphina veneriformis (Bivalvia: Veneridae) (2002) Korean Journal of Electron Microscopy, 32, pp. 303-310Pochon-Masson, J., Gharagozlou, I.D., Particularite morphologique de l'acrosome dans le spermatozoide de Tapes decussatus L. (Mollusque lamellibranche) (1970) Annales des Sciences Naturelles, Zoologie, 12, pp. 171-180Prieto, A.S., (1980) Contribuición A la Ecologia de Tivela Mactroides, 29, pp. 323-328. , Born, 1778: aspectos reprodutivos. Boletim do Instituto OceanográficoPrieto, A.S., (1983) Ecologia de Tivela Mactroides, 22, pp. 7-19. , Born, 1778 (Mollusca, Bivalvia) en playa Güiria (Sucre, Venezuela). Boletin del Instituto Oceanografico de Venezuela de la Universidad de OrienteReunov, A.A., Hodgson, A.N., Ultrastructure of the spermatozoa of five species of South African bivalves (Mollusca), and an examination of early spermatogenesis (1994) Journal of Morphology, 219, pp. 275-283Rouse, G.W., Jamieson, B.G.M., An ultrastructural study of the spermatozoa of the polychaetes Eurythoe complanata (Amphinomidae), Clymenella laseroni and Micromaldane laseroni (Maldanidae) with definition of sperm types in relation to reproductive biology (1987) Journal of Submicroscopic Cytology, 19, pp. 573-584Schaeffer-Novelli, Y., (1980) Análise Populacional de Anomalocardia Brasiliana, 29, pp. 351-355. , (Gmelin, 1791), na Praia do Saco da Ribeira, Ubatuba, Estado de São Paulo. Boletim do Instituto OceanográficoSoares, H.A., Schaeffer-Novelli, Y., Mandelli, J.R., (1982) Berbigão Anomalocardia Brasiliana, 9, pp. 21-38. , (Gmelin, 1791), bivalve comestível da região da Ilha do Cardoso, Estado de São Paulo, Brasil: aspectos biológicos de interesse para a pesca comercial. Boletim do Instituto de PescaSousa, M., Oliveira, E., An ultrastructural study of Crassostrea angulata (Mollusca, Bivalvia) spermatogenesis (1994) Marine Biology, 120, pp. 545-551Sousa, M., Guerra, R., Oliveira, E., Torres, A., Comparative PTA staining of molluscan spermatozoa (1998) Journal of Submicroscopic Cytology and Pathology, 30 (1), pp. 183-187Ying, X.L., Yang, W.X., Dahms, H.U., Un, Z.H., Chai Spermatozoa, X.L., And spermatogenesis in the northern quahaug Mercenaria mercenaria (Mollusca, Bivalvia) (2008) Helgoland Marine Research, 62 (4), pp. 321-32
