Epibenthic and benthopelagic medusae are rarely collected by standard benthic or pelagic sampling methods, and many species are considered uncommon and geographically restricted. Peer-reviewed scientific literature contains only two records of medusae belonging to the monotypic genus Tesserogastria Beyer, 1958 since their original description, both from the vicinity of the type locality in Oslofjord, contributing to an illusion of extreme rarity and restricted distribution. Our analysis of fresh samples and a thorough evaluation of all previous records of this taxon from both peer-reviewed scientific sources and “gray” literature show that the species is both more common and widespread than suggested by the scant records in primary scientific literature, and represents an example of an overlooked taxon in the epibenthos. High numbers of medusae of Tesserogastria musculosa Beyer, 1958 were collected at Raunefjord in western Norway. New data, together with validated observations from fjords in western and eastern Norway as well as western Sweden, demonstrate that the species is much more common than is evident from published records. Data on the mitochondrial 16S ribosomal RNA and cytochrome oxidase I molecular markers for the species are provided for the first time, as well as new observations on the morphology of living animals. Tesserogastria musculosa constitutes an example of a hydrozoan species with a misleading reported distribution, a situation likely to occur in all members of family Ptychogastriidae and other delicate epibenthic invertebrates. Sampling techniques specifically targeting the epibenthos and careful processing of the samples are essential for correctly assessing the presence of the species, suggesting that the lack of records for this and other epibenthic medusae may in part be an artefact of the commonly used sampling methods. A comparison of molecular data for species and genus delimitation in Ptychogastriidae, presented here for the first time, highlights the need for a thorough taxonomic revision of the family.

中文翻译：

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上皮水母中的稀有错觉：小家蝇（Tesserogastria musculosa）分布的事实和人工制品

上皮和底栖美杜莎很少通过标准的底栖或上层采样方法收集，许多物种被认为是不常见的且受地理限制。经过同行评审的科学文献仅包含两个属于单型属Tesserogastria Beyer（1958年）的水母的记录，因为它们的原始描述来自Oslofjord的类型区域附近，造成了极度稀有和有限分布的错觉。我们对新鲜样品的分析以及从同行评审的科学文献和“灰色”文献中对该分类单元的所有先前记录进行的全面评估表明，该物种比原始科学文献中较少记录所表明的更为普遍和广泛，并且代表了一个在鱼塘上被忽视的分类单元的例子。1958年，在挪威西部的Raunefjord收集到大量的Tesserogastria musculosa Beyer水母。新数据以及来自挪威西部和东部以及瑞典西部的峡湾的经过验证的观测结果表明，该物种比已发表的记录所显示的更为普遍。首次提供了该物种的线粒体16S核糖体RNA和细胞色素氧化酶I分子标记的数据，以及有关活体动物形态的新观察结果。Tmusrogastria musculosa构成了一个水生动物物种的例子，据报道具有误导性分布，这种情况很可能发生在鼠伤寒科的所有成员和其他脆弱的表皮无脊椎动物中。专门针对表皮动物的采样技术以及对样品的仔细处理对于正确评估物种的存在至关重要，这表明缺乏该和其他表皮美杜莎的记录可能部分是常用采样方法的伪影。首次在此处进行的鼠伤寒科的物种和属定界的分子数据比较显示出需要对该科进行彻底的分类学修订。