Wang Deng, Vannier Jean, Sun Jie, Yu Chiyang, Han Jian
State Key Laboratory of Continental Dynamics, Shaanxi Key Laboratory of Early Life & Environments and Department of Geology, Northwest University, Xi'an 710069, China.
Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China.
Biology (Basel). 2023 Sep 15;12(9):1242. doi: 10.3390/biology12091242.
The vast majority of early Paleozoic ecdysozoan worms are often resolved as stem-group Priapulida based on resemblances with the rare modern representatives of the group, such as the structure of the introvert and the number and distribution of scalids (a spiny cuticular outgrowth) and pharyngeal teeth. In Priapulida, both scalids and teeth create symmetry patterns, and three major diagnostic features are generally used to define the group: 25 longitudinal rows of scalids (five-fold symmetry), 8 scalids around the first introvert circle and the pentagonal arrangement of pharyngeal teeth. Here we describe gen. et sp. nov., a new priapulid from the early Cambrian Chengjiang Lagerstätte, characterized by an annulated trunk lacking a sclerotized ornament, four pairs of anal hooks and 16 longitudinal rows of scalids along its introvert and eight scalids around each introvert circle, giving the animal an unusual octoradial symmetry. Cladistic analyses resolve as a stem-group priapulid. also suggests that several biradial symmetry patterns (e.g., pentagonal, octagonal) expressed in the cuticular ornament, may have co-existed among early Cambrian priapulids and that the pentaradial mode may have become rapidly dominant during the course of evolution, possibly via the standardization of patterning, i.e., the natural selection of one symmetry type over others.
绝大多数早古生代蜕皮动物蠕虫通常根据与该类群稀有的现代代表的相似性，如内缩肌的结构、鳞片（一种带刺的表皮突出物）和咽齿的数量及分布，被归为鳃曳动物干群。在鳃曳动物中，鳞片和牙齿都形成对称模式，通常使用三个主要诊断特征来定义该类群：25排纵向排列的鳞片（五重对称）、围绕第一个内缩肌环的8个鳞片以及咽齿的五边形排列。在此，我们描述了一个寒武纪早期澄江生物群中的新鳃曳动物属及新物种，其特征为躯干具环纹但无硬化装饰，有四对肛门钩，沿内缩肌有16排纵向排列的鳞片，每个内缩肌环周围有8个鳞片，赋予该动物一种不寻常的八辐对称。分支系统分析将其归为鳃曳动物干群。这也表明，在寒武纪早期鳃曳动物中，可能同时存在几种在表皮装饰中表现出的双辐射对称模式（如五边形、八边形），并且五辐射模式可能在进化过程中通过模式标准化迅速占据主导地位，即一种对称类型相对于其他类型的自然选择。
