A juvenile orthocerid Dolorthoceras sp. from the Frasnian (Late Devonian) of the Polar Urals in NW Russia is the first recorded ectocochleate cephalopod showing fibrous structures and the first Devonian cephalopod preserving nacreous structures within its conch. Like Nautilus, Dolorthoceras sp. has columnar nacre in its shell wall and septa, which are composed of differentiated nacreous tablets that are c. 3 µm and 10 µm in diameter. The central, small, cylindrical, hollow siphonal tube—studied in median section using scanning electron microscope—comprises short columnar-nacreous suborthochoanitic septal necks and thin, apparently primarily chitinous, connecting rings; swollen, lens-shaped in median section, two-part fibrous non-biomineralized structures—here named clutches—envelope the posterior parts of the septal necks. Together with the adjacent connecting ring, the outer part of the clutch may extend onto adapical septal surfaces; their inner part and adjoining from inside next connecting ring line the septal neck. The clutches are comparable, to some degree, to the auxiliary deposits and cuffs of the siphonal tubes found in ammonoids; these are interpreted as being protective structures of the conjunctions between the connecting rings and septal necks reinforcing it against hydrostatic pressure, which was probably also the case in Dolorthoceras. Tracing the Silurian to Cretaceous longiconic cephalopods with narrow, central to eccentric, hollow siphonal tubes and swollen posterior portions of the septal necks shows that the Dolorthoceras-type siphonal tube may represent a conch structure that persisted throughout about 370 million-year-long evolutionary history of orthocerid cephalopods.

中文翻译：

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来自极地乌拉尔（俄罗斯西北部）的晚泥盆纪正统Dolorthoceras的虹吸管结构，保留了珍珠质和有机纤维及其在头足类动物进化中的持久性

少年的Orthocerid Dolorthoceras sp。来自俄罗斯西北部极地乌拉尔的弗拉斯尼人（晚泥盆世）是最早记录的具有纤维结构的外圆头足纲动物，也是最早的海螺内保存着珍珠质结构的泥盆纪头足动物。像鹦鹉螺，Dolorthoceras sp。在其壳壁和隔片中有圆柱状珍珠母，由分化的珍珠质片剂c组成。直径为3 µm和10 µm。中央的，细的，圆柱形的，空心的虹吸管-用扫描电子显微镜在中段进行了研究-包括短的圆柱状珠状蝶形隔正中隔颈和细的，显然主要是几丁质的连接环。中间部分呈肿胀状，透镜状，由两部分组成的纤维状非生物矿化结构（这里称为离合囊）将中隔颈后部包裹住。离合器的外部部分可以与相邻的连接环一起延伸到心尖的中隔表面上。它们的内部并从下一个连接环的内侧邻接隔颈。这些离合器在某种程度上可以与氨化物中虹吸管的辅助沉积物和袖口相媲美。这些被认为是连接环和中隔颈之间的连接处的保护结构，以增强其抵抗静水压力，这在Dolorthoceras中也可能是这种情况。追踪志留纪至白垩纪的长绒头足类动物，从中央到偏心狭窄，