Incunabula and perizonium of Neidium (Bacillariophyta).

Abstract

Abstract:The incunabula and perizonium of a paedogamous Neidium deme (in the N. ampliatum species complex) are described in detail using light and scanning electron microscopy. The incunabula contain two types of element, both heavily silicified. At each pole of the ellipsoidal zygote there is a large cap, which almost abuts its twin on either side of the zygote, beneath the gametangial valves. The caps are deeply and widely notched on their 'girdle' sides (i.e. on the sides of the zygote that underlie the gametangial girdle) and the space created by the notches is filled by large, almost triangular incunabular plates. Thus, on each side of the equator of the zygote there is one cap element and two plate elements. The caps overlap the plates and must precede them ontogenetically, creating a polarity opposite to that of the transverse perizonium. Both elements are sparsely and irregularly porous and have fimbriate margins. During auxospore expansion, the two sets of incunabular elements separate at the equator of the cell and the transverse perizonium is formed beneath, the incunabula continuing to form a tight seal around the perizonium and apparently constraining development to form a linear tube. All transverse perizonial bands possess delicate fimbriae and are open, even the primary band, which is slightly wider than the bands on either side and bears a median ridge. The open ends of the secondary bands sweep strongly towards the centre of the auxospore, producing a very obvious and wide suture. In expanded auxospores, a robust longitudinal band is found beneath the suture, which has coarser fimbriae than the transverse bands. Possible interpretations of the incunabular elements are discussed: no structures similar to the incunabular plates have been described in other diatoms, but it is known that related genera (Biremis, Muelleria) also have large cap-like elements in their incunabula. The open nature of the primary transverse perizonial band is unusual in raphid diatoms, but auxospore coverings have been investigated ultrastructurally in too few diatoms to permit detection of evolutionary trends.

Auxosporulation, morphology of vegetative cells and perizonium of Fallacia tenera (Hust.) D.G. Mann (Bacillariophyceae)

“…Grunow (1860: 511) (Mann 1982) and Neidium cf. ampliatum (Mann & Poulíčková 2009) are less than twice wider. In contrast, the primary transverse perizonial band of S. marvanii, Caloneis silicula (Ehrenb.)…”

“…For EM observation, vegetative cells were fixed with 2.5% glutaraldehyde, dropped on cover slips, 13-mm diameter for scanning electron microscope (SEM) observations, and treated by 70% nitric acids as described by Mann & Poulíčková (2009) or by boiling in a mixture of concentrated sulphuric and nitric acids. Auxospores were isolated from the mixed culture, transferred onto a cover slip (3-mm diameter or 13-mm diameter for SEM) and treated with NaClO followed by rinsing with distilled water repeatedly.…”

“…The ultrastructure of a perizonium in pennate diatoms has been reported in many species covering araphid (Sato et al 2004, Sato et al 2008a and raphid diatoms (Mann 1982, Toyoda et al 2005, Poulíčková & Mann 2006, Toyoda et al 2006, Kaczmarska et al 2007, Poulíčková et al 2007, Mann & Poulíčková 2009, Mann et al 2011. It also has been suggested that the ultrastructure of the perizonium has phylogenetic significance at higher taxonomic levels (Medlin & Kaczmarska 2004).…”

SCALY INCUNABULA, AUXOSPORE DEVELOPMENT, AND GIRDLE POLYMORPHISM IN SELLAPHORA MARVANII SP. NOV. (BACILLARIOPHYCEAE)1

“…A further kind of silicified incunabula is present in Neidium cf. ampliatum , where the zygote is completely surrounded by a robust, integrated system comprising two large hemiellipsoidal caps and four lateral plates (Mann and Poulíčková 2009); similar incunabula may exist in Muelleria and Scoliopleura (Edlund and Spaulding 2006).…”

“…In contrast, much narrower primary bands, at most double the width of the secondary bands, are apparently more common, occurring in, for example, Nitzschia (Trobajo et al. 2006), Neidium (Mann and Poulíčková 2009), and Rhoicosphenia (Mann 1982); further examples and discussion of the significance of primary band width are given by Poulíčková et al. (2007).…”