Li Wanying, Li Fengping, Liu Mingjie, Wang Aimin, Liu Chunsheng, Yang Yi
School of Marine Biology and Fisheries, Hainan University, Haikou 570228, China Hainan University Haikou China.
Sanya Nanfan Research Institute, Hainan University, Sanya 572025, China Sanya Nanfan Research Institute, Hainan University Sanya China.
Zookeys. 2025 Jul 4;1244:61-86. doi: 10.3897/zookeys.1244.139617. eCollection 2025.
Nudibranchs, also known as sea slugs, represent a high species diversity within Heterobranchia (Mollusca, Gastropoda); however, the systematics within this order remain controversial. The mitochondrial genome has been widely used in the phylogenetic reconstruction of mollusks, but the corresponding data on Nudibranchia are limited, hindering understanding of the phylogenetic relationships of this group. In the present study, the complete mitochondrial genomes of 11 species belonging to 8 families and 10 genera were newly sequenced and compared with the 64 previously published mitogenomes for analysis. All newly sequenced mitogenomes were double-stranded circular molecules ranging from 14,299 to 14,880 bp. A total of 37 genes, including 13 protein-coding genes (PCGs), two ribosomal RNA genes (rRNA), and 22 transfer RNA (tRNA) genes, were encoded among all species. Of these 37 genes, 24 are encoded on the heavy strand and 13 on the light strand. The mitogenomes showed variations in AT content, GC skew, and AT skew. The gene orders of Nudibranchia indicated that gene transpositions and inversion had occurred within . Based on the nucleotide sequences of 13 PCGs and 2 rRNA genes, the phylogenetic relationships of Nudibranchia have been reconstructed at family level. The phylogenetic analyses confirmed that Nudibranchia can be divided into Doridina and Cladobranchia with high support. However, the monophyly of Chromodoridoidea within Doridina is rejected due to the isolated positions of Actinocyclidae and Cadlinidae. Within Cladobranchia, the non-monophyly of Fionoidea was revealed since the fionoid group Coryphellidae clusters with Aeolidioidea. Molecular evidence, along with morphological characteristics, indicates that misidentifications of nudibranch species has been frequent in public databases. The present study suggests that the systematics within Nudibranchia needs further revision.
裸鳃亚目动物，也被称为海蛞蝓，是异鳃亚纲（软体动物门，腹足纲）中物种多样性较高的一类；然而，该目内的系统分类仍存在争议。线粒体基因组已被广泛应用于软体动物的系统发育重建，但裸鳃亚目动物的相应数据有限，这阻碍了对该类群系统发育关系的理解。在本研究中，新测序了8科10属11种裸鳃亚目动物的完整线粒体基因组，并与之前发表的64个有丝分裂基因组进行比较分析。所有新测序的有丝分裂基因组均为双链环状分子，长度在14299至14880 bp之间。所有物种共编码37个基因，包括13个蛋白质编码基因（PCG）、2个核糖体RNA基因（rRNA）和22个转移RNA（tRNA）基因。在这37个基因中，24个基因在重链上编码，13个在轻链上编码。有丝分裂基因组在AT含量、GC偏斜和AT偏斜方面表现出差异。裸鳃亚目动物的基因顺序表明基因转座和倒位在其内部发生。基于13个PCG和2个rRNA基因的核苷酸序列，在科级水平上重建了裸鳃亚目动物的系统发育关系。系统发育分析证实，裸鳃亚目动物可高度支持地分为多角海牛亚目和枝鳃海牛亚目。然而，由于辐肛海牛科和卡德海牛科的孤立位置，多角海牛亚目内的多彩海牛总科的单系性被否定。在枝鳃海牛亚目内，由于拟海牛科类群与海兔总科聚类，揭示了拟海牛总科的非单系性。分子证据以及形态特征表明，裸鳃亚目物种在公共数据库中经常被错误鉴定。本研究表明，裸鳃亚目内的系统分类需要进一步修订。
