Mandibles of representatives of the Holarctic crayfish families Astacidae, Cambaridae, and Cambaroididae were examined using SEM, and the results were analyzed in a phylogenetic framework. The intraspecific variability of the incisor process was found to be higher than its interspecific variability, mainly due to extensive abrasion of its ridge during intermolt periods. The plesiomorphic state of the crayfish mandibles highlights the dentate–crenate type of the incisor process and the extensive ribbed molar field with a multicuspidate caudal part, typical of the two parastacid crayfish examined for comparison. For Holarctic crayfish, the initial evolutionary type of the incisor is also the dentate–crenate one, but the molar field has a bowl‐shaped caudal part and reduced cephalic part, both of which have been shown, for example, for Cambaroides. Similar mandibles are also widely present in American cambarids, which further evolved a blade‐like incisor process (some Faxonius spp.) or a tricuspidate or double‐bladed caudal molar field (some Procambarus spp.). The molar field in Astacidae crayfish is subdivided and rugose. The results of the present study indicate that little phylogenetic information is conveyed by the mandible shape at the species or genus level. Evolutionary changes are indicated mainly on the level of the main crayfish families.

中文翻译：

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小龙虾下颌骨的比较形态，深入了解它们的进化

使用扫描电镜检查了 Holarctic 小龙虾科 Astacidae、Cambaridae 和 Cambaroididae 代表的下颌骨，并在系统发育框架中分析了结果。发现门牙过程的种内变异性高于其种间变异性，这主要是由于在蜕皮期间其脊部的广泛磨损。小龙虾下颌的同形状态突出了门牙 - 圆齿类型的门牙和具有多尖尾部分的广泛的棱纹磨牙区域，这是被检查以进行比较的两种寄生虫小龙虾的典型特征。对于 Holarctic 小龙虾，门牙的初始进化类型也是齿状-圆齿状的，但臼齿区域有一个碗状的尾部部分和减少的头部部分，这两个部分都已显示，例如，Cambaroides。类似的下颌骨也广泛存在于美洲海螯虾中，它们进一步进化出刀片状切牙突（一些 Faxonius spp.）或三尖瓣或双刃尾磨牙区（一些 Procambarus spp.）。Astacidae 小龙虾的臼齿区是细分的和有皱纹的。本研究的结果表明，在物种或属水平上，下颌骨形状传达的系统发育信息很少。进化变化主要表现在主要小龙虾科的水平上。本研究的结果表明，在物种或属水平上，下颌骨形状传达的系统发育信息很少。进化变化主要表现在主要小龙虾科的水平上。本研究的结果表明，在物种或属水平上，下颌骨形状传达的系统发育信息很少。进化变化主要表现在主要小龙虾科的水平上。