Problems in classification and identification of Synuraceae (Chrysophyceae)

Abstract

In the Synuraceae, the silica scales which cover the cell surface are of great taxonomic importance, although their delicate structure requires use of electron microscopy. Many species have been incompletely described by means of light microscopy, and there are serious difficulties in correlating them with species based on electron microscopy of the silica scales. The different types of variation in scale structure are described, and the variation range to be accepted within a species is discussed. However, as sexual reproduction is of rare occurrence in this family, the species concept must be highly arbitrary. It is reassuring then that many species based on scale ultrastructure also exhibit morphological and ecological characteristics. The advantages of scanning and transmission electron microscopy are emphasized for species identification and for detection of small forms with especially delicate scales.

Ultrastructure and assembly of the scale case inSynura(Synurophyceae Andersen)

“…The exact location of scales graded according to size on many species of Synura and Mallomonas (see especially Mallomonas eoa and M. akrokornos Takahashi, 1978, Plates 39 and 43 respectively), suggests that ultimately scales do have a particular destination in the scale case. This conclusion is supported by the more obvious distinctive arrangement of scales of differing morphology in specific regions of the scale case in Synura echinulata and some Mallomonas species (Harris, 1967;Kristiansen, 1979). If the ultimate destination of each developing scale in a scale case is predetermined then the sequence and location in which individual scales are deposited intracellularly would be expected to be highly ordered.…”

“…The morphology and arrangement of scales on the surface of Synura and Mallomonas cells have traditionally been the characters on which the taxonomy of these genera is based (Takahashi, 1978;Kristiansen, 1979). Apart from the possession of distinctive scale cases, Synura and Mallomonas also resemble each other in that the two flagella are inserted into the protoplast parallel to each other; they have similar flagellar root systems and a photoreceptor apparatus which consists of paired flagellar swellings that are not apparently associated with the cell membrane and chloroplast; no eyespot is present (Andersen, 1985;Wujek & Kristiansen, 1978).…”

Records of chrysophytes with siliceous scales (Mallomonadaceae and Paraphysomonadaceae) from Finnish inland waters

“…Kristiansen, 1979Kristiansen, , 1986, and a number of more or less constant subspecific taxa have been distinguished (cf. Nicholls & Gerrath, 1985, Siver, 1987.…”

Effect of temperature on size and shape of silica scales in Synura petersenii and Mallomonas tonsurata (Stramenopiles)

“…As silica structures remain preserved in lake sediments, synurophytes represent valuable bioindicators of either present or past environmental conditions (e.g., Rojackers & Kessels, 1986;Smol, 1995). However, even among scales belonging to one species, there is relatively great morphological variation (Kristiansen, 1979). Probably the most important factor affecting this variation is the position on the cell (Siver, 1991;Neustupa et al, 2010).…”