One of the most thoroughly studied marine snails in the world is the North Atlantic periwinkle Littorina littorea. In 2013, Buckland-Nicks et al. reported upon an “extensive community of organisms” living “inside” L. littorea in Nova Scotia, Canada. Conflicting with this report is a vast body of research on this snail since the mid-nineteenth century that has never identified the presence of such a taxonomically diverse endosymbiotic community, with the exception of a well-known assemblage of parasitic digenean trematodes that utilize the snail as a first-intermediate host. The absence of prior reports of a non-parasitic endosymbiotic community, and our own long-term observations, inspired us to study the biological community associated with L. littorea in two locations (Nova Scotia and Connecticut). We were unable to verify the endosymbiotic nature of any of the species (other than trematodes) noted by Buckland-Nicks et al. (Can J Zool 91:293–301, 2013) associated with L. littorea. Instead, we identified three likely sources of associated taxa reported by Buckland-Nicks et al. (Can J Zool 91:293–301, 2013) and by us: species were (1) ingested and defecated alive; (2) attached to the mucous-covered foot and drawn into the mantle cavity when the snail closed its operculum; and/or (3) associated with shell surface cracks and crevices, including within encrusting algae. We could not find any evidence that L. littorea hosts a diverse community of endosymbionts. Instead, we argue that the organisms interpreted as members of an endosymbiotic community by Buckland-Nicks et al. are instead free-living taxa that are transiently associated with the snails.

中文翻译：

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偶然的伙伴不是共生体：常见的长春花 Littorina littorea（软体动物：腹足类动物）内没有非寄生的内共生群落

世界上研究最彻底的海洋蜗牛之一是北大西洋长春花 Littorina littorea。2013 年，巴克兰-尼克斯等人。报道了加拿大新斯科舍省 L. littorea“内部”的“广泛的生物群落”。与本报告相矛盾的是，自 19 世纪中叶以来，对这种蜗牛的大量研究从未确定存在这样一个分类学上多样化的内共生群落，除了一个众所周知的利用蜗牛的寄生 digenean 吸虫组合作为第一中间宿主。没有关于非寄生内共生群落的先前报告，以及我们自己的长期观察，激励我们在两个地点（新斯科舍省和康涅狄格州）研究与 L. littorea 相关的生物群落。我们无法验证 Buckland-Nicks 等人指出的任何物种（吸虫除外）的内共生性质。（Can J Zool 91:293–301, 2013）与 L. littorea 相关。相反，我们确定了 Buckland-Nicks 等人报告的三个可能的相关类群来源。(Can J Zool 91:293–301, 2013) 和我们所说：物种被 (1) 活体摄入和排便；(2)附着于粘液覆盖的足部，当蜗牛关闭其鳃盖时被吸入地幔腔；和/或 (3) 与壳表面裂纹和裂缝有关，包括在结壳的藻类中。我们找不到任何证据表明 L. littorea 拥有多样化的内共生菌群落。相反，我们认为这些生物被 Buckland-Nicks 等人解释为内共生群落的成员。