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Three new species of Fallacia, F. miyajimensissp. nov., F. noduliferasp. nov., and F. similigemmiferasp. nov. are described from intertidal sediments in Japan. Their morphologies are studied with light, scanning and transmission electron microscopy. Fallacia miyajimensisdiffers from congeners in the presence of an apical pore, a finely porous conopeum possessing finger-shaped extensions with uniseriate rows of pores and a thick layer adjacent to the raphe with isolated depressions with small pores inside. Fallacia noduliferadiffers from congeners in the presence of a unique asymmetric internal central nodule. It can also be distinguished by the combination of stria density, conopeum with short extensions, and centrally convex lateral sterna. Fallacia similigemmiferadiffers from congeners by its lanceolate valve outline, more or less straight, distinct lateral areas and the presence of a rectelevatum on internal central nodule. We suggest that the structural combination of the structure of the conopeum and the lateral sterna is a stable feature in species discrimination and could be used to define species groups. The cingulum of F. similigemmiferacomprises a wide open valvocopula and two linear bands with different ligulae. This type of cingulum structure is also present in F. tenera, F. hodgeana, and probably in F. litoricolaand F. fractaas well, and likely occurs commonly in Fallacia.

DelphineisAndrews is a marine araphid pennate diatom genus belonging to the family Rhaphoneidaceae Forti, which has three distinct subgeneric groups around D. lineataAndrews, D. ovataAndrews and D. surirella(Ehrenberg) Andrews, respectively. Living cells and frustules of three taxa in the D. surirellagroup were studied using light and scanning electron microscopy. Delphineis minutissima(Hustedt) Simonsen is characterized by small, circular to elliptical valves in which the sternum is as narrow as the virgae. The valve outline of D. surirellais broadly elliptical to lanceolate and the straight sternum is laterally expanded at the apices. Delphineis australiscomb. nov. has broadly elliptical valves and a sternum that is slightly narrower at the middle of the valve. Delphineis minutissimaand D. surirellashare the following fine structure features; no granules, plated rota with two spokes, two rimoportulae per valve and two small pores at each apex. The epicingulum of D. minutissimaand D. surirellais composed of several open bands; the first and second bands open at opposite ends, the more distal bands are short.

Three marine araphid diatoms species, Grammatophora angulosaEhrenberg, G. arcuataEhrenberg and G. hamuliferaKiltzing, were examined in light (LM) and scanning electron microscopy (SEM), including sections treated by a Focused-Ion-Beam system. Observations of sequential changes of septa morphology with cell size reduction revealed that a septum-body and a septum-base are connected at species-specific angle, θ, which can be used as the distinguishing character of each species under light microscopy (LM). θ is equal to ± a right angle for G. angulosa, to an obtuse angle for G. arcuataand to an acute angle for G. hamulifera.Observations of sections under SEM illustrated an interlocking mechanism of the pseudoseptum of a valve with a hooked part of a valvocopula. The presence of this physical interlocking system in G. angulosaand G hamuliferacan be seen as a short, dark line between the valve and the valvocopula under LM, and is likely a sophisticated structure to keep the physical link between the valve and the valvocopula. The morphological features of three species under the LM and SEM are compared.

The morphology and fine structure of two marine mooraphid diatoms, Achnanthes javanicaGrunow and A. subconstricta(Meister) comb. Nov. (= A javanica var. subconstrictaMeister) have been investigated.Observations on the valves of type material (Grunow in Cleve & Möller 1878) of A. javanicashow them to be lanceolate to linear in shape with a marginal ridge on the araphid valve but lacking terminal orbiculi. Conversely, A. subconstictahas a marginal ridge and special marginal spines as well as terminal orbiculi. From SEM observations in girdle view, A. subconstricta. These features support the view that A. subconstrictashould be considered an independent species.

The morphology and fine valve structure of the marine attached diatom Cocconeis pseudomarginataGregory var. intermediaGrunow was investigated. The entire frustule, internal and external structures of the raphid and araphid valves and complete cingulum are described using not only the light microscope and scanning and transmission electron microscope but also bleaching method and the focused ion beam technique. The raphe that terminates with a comma-shaped helictoglossa internally is slightly sigmoid. The hymenes, with perforations arranged in a centric array, are located near the internal openings of the areolae in the raphid valve (RV). The striae in the araphid valve (AV) consist of alveoli occluded by hymenes that have perforations arranged in a parallel array and locate near the outer surface. The complete cingulum of AV consists of an afimbriate, open valvocopula and two bands with small ligula. The RV has only a valvocopula which is open type and not fimbriate.