ABSTRACT Four species of Gomphonema described by Hustedt with fusiform valve shape are studied for the first time using SEM. G. longissimum Hustedt, G. angustissimum Hustedt, G. woltereckii Hustedt and G. subtiliforme Hustedt were described, and are known only, from the ancient Malili lake system in Indonesia. Molecular investigations of two cultured strains of G. longissimum, using 18S rDNA and rbcL, are presented. In terms of morphology, these four species have unusually long valves and a fusiform shape otherwise unknown in Gomphonema, yet morphological similarities with other species include C-shaped or semi-circular areolae, uniseriate striae, pseudosepta, apical pore fields, a straight raphe with hooked internal proximal ends and a typical stigma in G. longissimum and G. angustissimum. Results of the molecular study support placement of G. longissimum with other ‘typical’ Gomphonema species. G. subtiliforme and G. woltereckii both lack a stigma. G. subtiliforme is similar in shape and morphology to members of the group G. subtile Ehrenberg, which all bear stigmata. G. woltereckii differs from G. longissimum and G. angustissimum by having areolae that are semi-circular, not C-shaped, and by the absence of a stigma. Therefore, based on morphology, we conclude these extraordinarily large Gomphonema taxa are similar to each other and generally resemble other species of the genus, yet there is enough variation in presence/absence of stigmata and structure of the areolae that they do not necessarily form a distinct group. Thus, despite their large size, and presence in the same lake system, we cannot conclude they form a species flock. Less than two dozen Gomphonema species are present in Malili lakes whereas some other ancient lakes, such as Lake Baikal, have many more species and exhibit species flocks.

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马里湖（印度尼西亚）最长 Gomphonema 及相关分类群的形态学和分子学研究及对古湖泊硅藻演化的评论

摘要 利用扫描电镜首次研究了 Hustedt 描述的四种具有梭形瓣膜形状的 Gomphonema。G. longissimum Hustedt、G. angustissimum Hustedt、G. woltereckii Hustedt 和 G. subtiliforme Hustedt 在印度尼西亚的古代马里湖系统中被描述过，并且仅被知晓。介绍了使用 18S rDNA 和 rbcL 对 G. longissimum 的两个培养菌株进行的分子研究。在形态方面，这四个物种具有异常长的瓣膜和梭形形状，在 Gomphonema 中是未知的，但与其他物种的形态相似性包括 C 形或半圆形乳晕、单列条纹、假隔、顶端孔场、直缝钩状的内部近端和 G. longissimum 和 G. angustissimum 的典型柱头。分子研究的结果支持 G 的放置。与其他“典型” Gomphonema 物种最长。G. subtiliforme 和 G. woltereckii 都没有柱头。G. subtiliforme 在形状和形态上与 G. subtile Ehrenberg 组的成员相似，它们都带有柱头。G. woltereckii 与 G. longissimum 和 G. angustissimum 的不同之处在于具有半圆形而非 C 形的乳晕，并且没有柱头。因此，基于形态学，我们得出结论，这些非常大的 Gomphonema 分类群彼此相似，并且通常与该属的其他物种相似，但是在柱头的存在/不存在和乳晕结构方面存在足够的差异，因此它们不一定形成一个独特的群体。因此，尽管它们的体型很大，并且存在于同一湖泊系统中，但我们不能断定它们形成了一个物种群。