Some algae are known to grow on shellfish shells. Most of these have been reported in aquatic environments. The species specificity for substrate shells varies, and some algae grow only on the shells of a certain species of shellfish, such as Pseudocladophora conchopheria (Cladophorales, Ulvophyceae) on Lunella coreensis (Trochida, Gastropoda). There are very few reports of algae that grow on land snails. In this study, we discovered green algae growing on the shells of six species of door snails (Clausiliidae) from nine localities in Japan. These green algae formed a green mat composed of thalli embedded in the extracellular matrix. The thallus was composed of aggregated oval cells and peripheral branched filaments. The cells possessed a single parietal chloroplast with a pyrenoid surrounded by two starch sheaths and transversed by a thylakoid. Oil droplets in the cell and ring-like structures on the cell wall surface were frequently observed. The 18S rDNA sequences of all shell-attached algae on different clausiliid species from different localities were almost identical and formed a new clade in the family Kornmanniaceae (Ulvales, Ulvophyceae). No other algae forming visible colonies on the clausiliid shell were found. These findings indicate the presence of specificity between the alga and clausiliid shells. Based on the results of morphological observation and molecular phylogenetic analysis, we propose a new genus and new species of shell-attached green alga, Annulotesta cochlephila.

已知一些藻类生长在贝类壳上。其中大部分已在水生环境中得到报道。底质壳的物种特异性各不相同，有些藻类只生长在某种贝类的壳上，例如Lunella coreensis上的Pseudocladophora conchopheria (Cladophorales, Ulvophyceae)（Trochida，腹足动物）。很少有关于在陆生蜗牛身上生长藻类的报道。在这项研究中，我们发现在日本九个地方的六种门蜗牛 (Clausiliidae) 的壳上生长着绿藻。这些绿藻形成了一个由嵌入细胞外基质中的菌体组成的绿色垫子。菌体由聚集的椭圆形细胞和周围分枝的丝状体组成。这些细胞拥有一个单一的顶叶叶绿体和一个被两个淀粉鞘包围并被类囊体横穿的核蛋白。经常观察到细胞内的油滴和细胞壁表面的环状结构。来自不同地区的不同clausiliid物种的所有壳附藻的18S rDNA序列几乎相同，并且在Kornmanniaceae（Ulvales，Ulvophyceae）中形成了一个新的进化枝。没有发现其他藻类在 clausiliid 壳上形成可见的菌落。这些发现表明藻类和 clausiliid 壳之间存在特异性。根据形态学观察和分子系统发育分析的结果，我们提出了壳附绿藻新属新种，Annulotesta cochlephila。