Ultrastructuralstudies on some Mastogloia (Bacillariophyceae) species belonging to the group sulcatae

Seven species of the diatom genus Mastogloia Thwaites ex W. Smith (group Sulcatae; Hustedt 1933) were studied using transmitted light and scanning electron microscopy. Specimens for study were collected from the Indian River, Florida, U.S.A. (salinity 16-42‰, temperature 9-34 ͦC) as epiphytes on Halodule wrightii Asherson. The silicious structure of M. braunii, M. hustedtii, M. minutissima, M. omissa, M. pisciculus, M. pumila var. pumila and M. punila var. papuarum is described. Three types of locular systems are described based on the development of locular tubes. Only one of these types of locular systems was found in the seven species included in this study. In this type of system, locular tubes are situated in the same plane as the loculi. These tubes are short and connect loculi to external locular pores which are removed from parent loculi toward valve apices. Structure of elements of the striae is discussed. Differences in the formation of lateral areas, especially on the external valve face, are described for the species studied.