Characterisation of the haemocytes of leaf oysters, <i>Isognomon ephippium</i> (Linnaeus, 1758)

Characterisation of the immune system of bivalves can be a key to understanding their adaptation and resilience to the environment. This study is the first to characterise the haemocytes of the Family Isognomonidae. Three different types of haemocytes, granular cells, hyalinocytes and blast-like cells, were identified by light microscopy in leaf oysters <i>Isognomon ephippium</i> (Linnaeus, 1758), with relative proportions of 8.4% (±2.3%) 76.2%, (±1.9%), and 15.3% (±1.6%), respectively, determined by flow cytometry. Scanning electron micrographs illustrated the outer appearance of the major haemocyte types, including dendritic-like cytoplasmic extensions on activated haemocytes. The total haemocyte count (THC) and bacterial counts in the haemolymph of leaf oysters, as well as the bacterial load in the source water, were compared across three estuaries with differing water quality on the north coast of New South Wales, Australia. THC ranged from 3.89 × 10⁵–2.89 × 10⁶ cells/mL in leaf oysters and significantly differed among three sites. THC increased with nitrogen, but decreased with higher bacterial loads in the water, which in turn correlated to other water quality parameters. This study provides baseline information on the leaf oyster immune system to facilitate future monitoring of <i>Isognomon</i> health in relation to environmental stressors.双壳类（bivalves）免疫系统的表征研究，是解析其环境适应性与抗逆能力的关键所在。本研究首次对障泥蛤科（Isognomonidae）的血细胞（haemocytes）开展系统表征：通过光学显微镜，在鞍背障泥蛤（*Isognomon ephippium*，Linnaeus, 1758）体内鉴定出三种血细胞类型——颗粒细胞、透明细胞与类胚细胞；经流式细胞术（flow cytometry）检测，三者的相对占比分别为8.4%（±2.3%）、76.2%（±1.9%）与15.3%（±1.6%）。扫描电子显微镜（scanning electron micrographs）图像展示了主要血细胞类型的外观特征，包括活化血细胞表面的树突状胞质突起。本研究选取澳大利亚新南威尔士州北海岸三个水质各异的河口作为采样位点，对比了鞍背障泥蛤血淋巴中的血细胞总数（total haemocyte count, THC）与细菌计数，以及其源水中的细菌载量。鞍背障泥蛤的血细胞总数范围为3.89×10⁵~2.89×10⁶ 个/毫升，且三个采样点的血细胞总数存在显著差异。研究发现，血细胞总数随水体氮含量升高而上升，但随水中细菌载量增加而下降，该相关性同时与其他水质参数存在关联。本研究为鞍背障泥蛤的免疫系统提供了基础数据，可为未来开展障泥蛤属（*Isognomon*）健康状况与环境胁迫因子相关性的监测工作提供支撑。