Phylogenomic analysis and morphological data suggest left-right swimming behavior evolved prior to the origin of the pelagic Phylliroidae (Gastropoda: Nudibranchia)

Evolutionary transitions from benthic to pelagic habitats are major adaptive shifts. Investigations into such shifts are critical for understanding the complex interaction between co-opting existing traits for new functions and novel traits that originate during or post-transition. Gastropod mollusks are of particular interest in regard to benthic-pelagic evolutionary transitions, as shifts from benthic to pelagic habitats are uncommon. Phylliroe is one such pelagic lineage in Phylliroidae, a family of holoplanktonic nudibranchs with a highly aberrant morphology that appears to be adapted for life in the pelagic zone. However, the phylogenetic placement of this enigmatic group of pelagic nudibranchs has never been investigated. Here we present phylogenomic analyses which place Phylliroe within a group of nudibranchs called Dendronotida sensu stricto. We also discuss a subset of the morphological and behavioral features that Phylliroe shares with other closely related lineages (Dendronot...

底栖至浮游生境的演化过渡属于重要的适应性转变。针对这类转变开展研究，对于解析利用现有性状实现新功能，与过渡阶段或过渡后起源的新颖性状之间的复杂互作机制，具有关键意义。腹足类软体动物（Gastropod mollusks）在底栖-浮游演化过渡的相关研究中备受关注，因为从底栖向浮游生境的转变实属罕见。叶海牛属（Phylliroe）是叶海牛科（Phylliroidae）下的一类浮游支系，该科为全浮游裸鳃类（holoplanktonic nudibranchs），其形态高度特化异常，似乎已适配浮游带的生存环境。然而，这类神秘的浮游裸鳃类类群的系统发育位置，此前从未得到研究。本研究开展了系统基因组学分析，将叶海牛属归入狭义枝鳃目（Dendronotida sensu stricto）的一个类群中。我们还探讨了叶海牛属与其他近缘支系（枝鳃目狭义类群……）共有的部分形态与行为特征。