Cryptic speciation yields remarkable mimics: A new genus of sea slugs that masquerade as toxic algae (Caulerpa spp.)

“Cryptic” can refer to species that match their background through camouflage or disruptive coloration, or in taxonomy to externally similar but unrecognized congeners. In adaptive resemblance, organisms resemble parts of a larger host animal or plant on which the mimic is highly cryptic. Mimetic lineages that radiate onto superficially similar hosts may contain cryptic species in both senses: taxa that are difficult to detect, and challenging for taxonomists to distinguish. Here, we describe a new genus and four species of herbivorous sea slugs (Gastropoda, Heterobranchia, Sacoglossa), including remarkable mimics of toxic green algae (Caulerpa spp.) on which the slugs feed. The long-recognized Stiliger smaragdinus Baba 1949 is highly mimetic of ‘sea grapes’ (C. racemosa-lentilifera), but phylogenetic analyses of four genes indicated Stiliger was polyphyletic: the name-bearing species grouped within Placida, whereas Caulerpa-mimetic lineages were phylogenetically distinct. We erect the ...“隐蔽（Cryptic）”一词可指代通过伪装（camouflage）或破坏色（disruptive coloration）与环境背景融为一体的物种，也可在分类学（taxonomy）中用于描述外形相似但尚未被识别的同属物种（congeners）。在适应性拟态（adaptive resemblance）中，拟态生物会拟态其赖以高度隐蔽的更大宿主动植物的部分结构。辐射演化至外观相似宿主的拟态支系，可能同时包含两种意义上的隐蔽物种：一是难以被发现的类群，二是令分类学家难以区分的类群。本文记述了一个新属及四种植食性海蛞蝓（腹足纲Gastropoda、异鳃类Heterobranchia、囊舌目Sacoglossa），其中包括一类可高度拟态其取食的有毒绿藻——蕨藻属（Caulerpa spp.）的类群。此前被广泛认可的Stiliger smaragdinus Baba 1949高度拟态“海葡萄”（C. racemosa-lentilifera），但基于4个基因的系统发育分析显示，Stiliger属为多系群：其模式物种隶属于Placida属，而蕨藻拟态支系在系统发育上独立自成一类。我们建立了……