Lightiella serendipitaJones, 1961 was first discovered in San Francisco Bay, California in 1953, but it had not been observed since 1988. In 2017, a total of 13 adult L. serendipita specimens were found as part of a study in central San Francisco Bay, nearly doubling the total number of specimens ever collected. We measured vertical distribution of macroinvertebrates and environmental variables, including grain size and chemical composition of sediment samples, to evaluate potential features associated with the habitat of the species. Specimens were generally found in sediments with low organic matter (1.7–3%), high sulfate concentrations (594.6–647 ppm SO₄), fine grain size (12.8–36.2% sand, 35.6–58% silt, 22.8–37.6% clay) and were mostly found in deep core sections (4–10 cm). Specimens were also consistently observed in cores containing tube-forming Polychaeta (i.e., Sabaco elongatus (Verrill, 1873) and Capitellidae), suggesting L. serendipita may have a commensal relationship with sedentary polychaetes, as do other cephalocaridans such as Lightiella incisaGooding, 1963. We provide a scanning electron micrograph of L. serendipita and the first complete key to the species in class Cephalocarida to help elucidate the taxonomy of this rare crustacean taxon. The perceived absence of L. serendipita in previous surveys of the Bay may be attributable to its rarity; however, additional research is needed to fully understand habitat requirements and population size of this unique endemic species.

中文翻译：

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1961年在美国加利福尼亚州旧金山湾重新发现了马蹄虾Lightiella serendipita Jones（Cephalocarida：Hutchinsoniellidae），这是世界头孢螨科物种的关键

柠檬小卷心菜1961年的Jones于1953年首次在加利福尼亚州的旧金山湾被发现，但自1988年以来一直未观察到。2017年，在旧金山湾中部的一项研究中，共发现了13个成年的L. serendipita标本，几乎收集的标本总数翻倍。我们测量了大型无脊椎动物的垂直分布和环境变量，包括颗粒大小和沉积物样品的化学成分，以评估与物种栖息地相关的潜在特征。通常在低有机质（1.7–3％），高硫酸盐浓度（594.6–647 ppm SO ₄）的沉积物中发现标本。），细粒度（沙子为12.8–36.2％，淤泥为35.6–58％，粘土为22.8–37.6％），且大多位于深部岩心段（4–10 cm）中。在含有管状形成的Polychaeta（即Sabaco elongatus（Verrill，1873）和Capitellidae）的岩心中也能持续观察到标本，这表明serendipita L.和久坐的多毛cha可能有共同的关系，其他头足纲动物如Lightiella incisa也是如此。Gooding，1963年。我们提供了Serendipita L.的扫描电子显微照片以及头孢螨科中第一个完整的物种密匙，以帮助阐明这种罕见的甲壳类生物分类。在海湾以前的调查中，感觉不到L. serendipita可能是由于其稀有性所致；但是，还需要进行其他研究才能充分了解这种独特特有物种的栖息地要求和种群数量。