Allgemeine und Spezielle Zoologie, Institut für Biowissenschaften, Universität Rostock, Rostock, Germany.
J Morphol. 2020 Dec;281(12):1547-1566. doi: 10.1002/jmor.21268. Epub 2020 Oct 27.
Swimming crabs of the taxon Portunoidea show specialized, paddle-shaped fifth pereiopods (P5), which play a role in these crabs' ability to swim. In this study, the morphology of the fifth pereiopod in swimming and non-swimming crabs was studied in detail and the mobility in the articulations between podomeres was calculated from reconstructed three-dimensional (3D)-models. This way, we aimed to provide new estimates of kinematic parameters, and to answer the question on a possible homology of the P5 within several portunoid clades. We measured and compared podomere length ratios, orientations of the joint axes, and modeled single range of motion (sROM) of each joint as well as the total range of motion (tROM) of all joints of the P5 as a whole. Seven Portunoidea species, four of them belonging to the P5-swimming crab morphotype (Liocarcinus depurator, Polybius henslowii, Callinectes sapidus, Portunus pelagicus) and three not belonging to this morphotype (Carcinus aestuarii, Portumnus latipes, and with uncertain status Carupa tenuipes) were compared with the non-portunoids Sternodromia monodi, Ranina ranina, Raninoides bouvieri, Eriocheir sinensis, Varuna litterata, Ashtoret lunaris, and Cancer pagurus. The study was carried out using a combination of microcomputer tomography (μCT)-techniques and 3D-reconstructions. The μCT-data were used to create surface models of the P5 in Amira, which were then 3D-animated and manipulated in Maya to qualitatively compare modeled kinematic parameters. Results show that the merus and carpus in swimming crabs are shorter than in non-swimming crabs, while sROM angles are generally larger. The tROM of all joints expressed as Euclidean distances is generally higher in the portunoids (except for Carcinus). Our comparison of the complete trajectory of the dactylus tip regarding all maximum joint positions of the studied species suggests that the P5-swimming leg might have evolved once in the Portunoidea and got lost afterward in certain clades.
十足目游泳蟹类具有特化的桨状第五步足（P5），这对于它们的游泳能力至关重要。在这项研究中，我们详细研究了游泳蟹和非游泳蟹的第五步足形态，并通过重建的三维（3D）模型计算了各跗节关节的活动性。这样，我们旨在提供新的运动学参数估计，并回答关于几个梭子蟹科内 P5 同源性的问题。我们测量并比较了各跗节的长度比、关节轴的方向，以及单个运动范围（sROM）和整体 P5 的总运动范围（tROM）。我们比较了 7 种十足目物种，其中 4 种属于 P5 游泳蟹形态型（李氏泥蟹、亨氏真蟹、美洲红蟹、远海梭子蟹），3 种不属于这种形态型（三疣梭子蟹、中华绒螯蟹和 Carupa tenuipes 的状态不确定），以及非梭子蟹科的 Sternodromia monodi、Ranina ranina、Raninoides bouvieri、中华绒螯蟹、Varuna litterata、Ashtoret lunaris 和 Cancer pagurus。这项研究使用了微计算机断层扫描（μCT）技术和 3D 重建的组合。μCT 数据用于在 Amira 中创建 P5 的表面模型，然后在 Maya 中对其进行 3D 动画和操作，以定性比较模型化的运动学参数。结果表明，游泳蟹的长节和腕节比非游泳蟹短，而 sROM 角度通常更大。所有关节的 tROM 以欧几里得距离表示，在梭子蟹科中一般较高（除了 Carcinus）。我们比较了所有研究物种的跗节末端的完整轨迹和最大关节位置，表明 P5 游泳足可能在十足目进化过程中只出现过一次，之后在某些科中丢失了。
