ABSTRACT. The Widemouth Blindcat, Satan eurystomus Hubbs and Bailey 1947, was the second of four stygobitic species of Ictaluridae discovered in the subterranean waters of southern Texas and northeastern Mexico. The skeletal anatomy of Satan has been scarcely known from a few, dated radiographs. Using additional radiographs and high resolution CT-datasets for two well-ossified specimens, we applied high-resolution X-ray computed tomography (HRXCT) to visualize, illustrate and describe the bony skeleton of Satan. We also provide an online archive of still and animated tomographic images of the skeletal anatomy of this little-known species. The skeleton and soft anatomy of Satan are distinctive. Twelve skeletal autapomorphies are described that singularly distinguish Satan within Ictaluridae and, probably in combination, from all other catfishes. Some of these are reductive losses or simplifications of skull bones (e.g. loss of one infraorbital bone; reduced ornamentation of the pterotic bone) and joint complexity (e.g. simple overlapping frontal-lateral ethmoid articulation; loosely ligamentous interopercle-posterior ceratohyal joint). Some of the autapomorphies are anatomically and perhaps developmentally complex (e.g. a novel series of three midline joints closing a middle span of the posterior cranial fontanel; a deeply excavated temporal fossa and an unusually enlarged interhyal bone). The tiny dorsal-fin spinelet (first lepidotrich) of Satan has a novel peaked and twisted shape. Ten apparent and exclusive synapomorphies within Ictaluridae gathered from this and previous studies suggest that Satan and Pylodictis are closest relatives. Most of these are functionally related to prey detection and suction feeding: fusion of the symphyseal mandibular sensory pores and increase in the number of preoperculo-mandibular canal pores; depressed, flattened heads and wide transverse mouths; prominent posterior process of the lateral ethmoid alongside and below the frontal bone margin; vertical and blade-like supraoccipital posterior process; unique arrangement of the parasagittal and occipital muscleattachment crests on the skull roof; large triangular panel of integument within the operculum framed by the opercle, preopercle and interopercle bones; elongated posterior ceratohyal; and, form of the fourth supraneural and loss of its anterior nuchal plate. In contrast, 15 synapomorphies recovered by Arce-H. et al. 2016, are confirmed suggesting that Satan is one of the four stygobitic ictalurids comprising a “Troglobites” subclade within the family: (Trogloglanis, Satan, Prietella phreatophila, P. lundbergi). These features include three stygomorphic and reductive apomorphies that are exclusive within Ictaluridae: loss of fully developed eyes and pigmentation, and simplification of the fifth vertebra and its joint with the Weberian apparatus. Twelve other synapomorphies shown by the Troglobites are also apparent homoplasies of character states shared with various other ictalurids. These include reductive characters such as shortened lateral line canal, reduced infraorbitals and underdeveloped or incomplete ossifications of the pterotic, supraoccipital, hyoid arch bones and transcapular ligament. Also, the Troglobites and various other ictalurids have: an adnate adiposecaudal fin, foreshortened anterior cranial fontanelle, reduced ventral wings of the frontal bone, replacement of bone by cartilage in hypohyal joints; incompletely ossified transcapular ligament, and consolidation of some hypural bones. Completing a full morphological character dataset across the Troglobites has been impeded by incomplete specimen preparations and study of P. lundbergi and to a lesser extent, P. phreatophila and Trogloglanis.

中文翻译：

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撒旦的骨骼揭示：撒旦 eurystomus，地下宽口盲猫（Siluriformes，Ictaluridae）的断层扫描和比较骨学

摘要。Widemouth Blindcat，Satan eurystomus Hubbs 和 Bailey 1947，是在德克萨斯州南部和墨西哥东北部的地下水域发现的四种 Ictaluridae 物种中的第二种。从几张过时的射线照片中，人们几乎不知道撒旦的骨骼解剖结构。我们对两个骨化良好的标本使用额外的 X 光片和高分辨率 CT 数据集，应用高分辨率 X 射线计算机断层扫描 (HRXCT) 来可视化、说明和描述撒旦的骨骼。我们还提供了这个鲜为人知的物种骨骼解剖结构的静态和动画断层扫描图像的在线档案。撒旦的骨骼和柔软的解剖结构与众不同。描述了 12 种骨骼自体变形体，它们在 Ictaluridae 中单独区分了撒旦，并且可能在组合中与所有其他鲶鱼区分开来。其中一些是颅骨的减少性损失或简化（例如，一个眶下骨的损失；翼骨的装饰减少）和关节复杂性（例如简单重叠的额侧筛骨关节；松散的韧带间鳃盖骨间 - 后角板关节）。一些自体变形在解剖学上和可能在发育上是复杂的（例如，封闭后颅囟的中间跨度的三个中线关节的新系列；深挖颞窝和异常扩大的玻璃间骨）。撒旦的微小背鳍尖刺（第一鳞翅目）具有新颖的尖顶和扭曲形状。从这项研究和之前的研究中收集到的八爪鱼科中的 10 种明显且独特的突触表明，Satan 和 Pylodictis 是最亲近的亲戚。其中大部分在功能上与猎物检测和吸食有关：下颌联合感觉孔的融合和下颌前鳃管孔的数量增加；低沉、扁平的头部和宽阔的横向嘴；侧筛骨的后突位于额骨边缘旁边和下方；垂直和刀片状的枕上后突；颅顶上的矢状旁肌和枕骨附着嵴的独特排列；由鳃盖骨、鳃盖骨前骨和鳃盖骨间骨构成的鳃盖内的大三角形珠被；拉长的后角玻璃；并且，第四神经上神经的形式和其前项骨板的丢失。相比之下，Arce-H 恢复了 15 个突触。等。2016年，被证实表明撒旦是四个 stygobitic ictalurids 之一，包括家族内的一个“Troglobites”分支：（Trogloglanis、Satan、Prietella phreatophila、P. lundbergi）。这些特征包括鸭科独有的三种隐匿性和还原性异形：完全发育的眼睛和色素沉着的丧失，以及第五椎骨及其与韦伯氏装置的关节的简化。Troglobites 显示的其他十二种突触也是与各种其他 ictalurids 共享的特征状态的明显同质性。这些包括减少特征，例如缩短的侧线管，减少的眶下和翼骨，枕上，舌骨和经肩胛韧带的不发达或不完全骨化。此外，Troglobites 和其他各种 ictalurids 有：贴附的脂肪尾鳍，缩短的前颅囟门，减少额骨的腹翼，在下透明关节中用软骨代替骨骼；不完全骨化的经肩胛韧带，和一些hypural骨的巩固。完成整个 Troglobites 的完整形态特征数据集受到不完整的标本制备和对 P. lundbergi 的研究以及较小程度上的 P. phreatophila 和 Trogloglanis 的阻碍。