小嵌套曲菌（学名：Aspergillus nidulans），又称为构巢曲霉、构巢曲霉或钩巢曲霉等名称，有一异名构巢裸胞壳（Emericella nidulans），是属于子囊菌门的一种丝状真菌。它已经成为真核生物细胞生物学上一个重要研究生物对象超过50多年，它被研究的学术主题领域相当地广，这些主题包括了遗传重组、去氧核糖核酸修复、突变、细胞周期控制、致病原理（pathogenesis）与代谢等等。小嵌套曲菌在它所属的曲菌属（Aspergillus）之中是少数可以经由在实验室中菌株交互减数分裂来形成有性孢子的其中一种物种。小嵌套曲菌是一种雌雄同体（homothallic）真菌，这是指小嵌套曲菌可以自花授粉（self-fertilize），并且在没有其他交配个体的情形下形成子实体（sporocarp，或称孢子果，fruiting body）。

Aspergillus nidulans (also called Emericella nidulans when referring to its sexual form, or teleomorph) is one of many species of filamentous fungi in the phylum Ascomycota. It has been an important research organism for studying eukaryotic cell biology for over 50 years, being used to study a wide range of subjects including recombination, DNA repair, mutation, cell cycle control, tubulin, chromatin, nucleokinesis, pathogenesis, metabolism, and experimental evolution. It is one of the few species in its genus able to form sexual spores through meiosis, allowing crossing of strains in the laboratory. A. nidulans is a homothallic fungus, meaning it is able to self-fertilize and form fruiting bodies in the absence of a mating partner. It has septate hyphae with a woolly colony texture and white mycelia. The green colour of wild-type colonies is due to pigmentation of the spores, while mutations in the pigmentation pathway can produce other spore colours.