THE PRO-OSTRACUM AND PRIMORDIAL ROSTRUM AT EARLY ONTOGENY OF LOWER JURASSIC BELEMNITES FROM NORTH-WESTERN GERMANY
THE PRO-OSTRACUM AND PRIMORDIAL ROSTRUM AT EARLY ONTOGENY OF LOWER JURASSIC BELEMNITES FROM NORTH-WESTERN GERMANY
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德国西北部下侏罗统箭锰矿早期个体发育时的前基质和原始喙台
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
W. Weitschat
中科院分区：
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作者：
L. Doguzhaeva;H. Mutvei;W. Weitschat
下侏罗统箭石中的原介板和原始喙的结构出现在早期的个体发育阶段，暂归属于？来自德国西北部的Passaloteuthis。首次在第一层锥中观察到原角质层。在早期贝壳个体发育中存在原介层支持了Naef（1922）的观点，即箭石在其整个个体发育过程中具有内部骨骼，从最早的孵化后阶段开始。这一解释以前曾受到几位作家的质疑。研究了幼原介层的外表面和内表面。这些表面的总体形态与成年个体发育阶段相似。中间部分显示，原介层由三个薄层组成：一个内部和外部棱柱层分开的细层状，主要是有机层。这些层从圆锥壳的背侧延伸到腹侧。本文获得的信息证实了原介层代表外耳蜗形头足类外壳中不存在的结构的想法（Doguzhaeva，1999，Doguzhaeva等人，1999 b，2002 a）。原始喙围绕着原贝壳，并继续作为一个独特的棱柱层沿着的Phragmocone，至少沿着第一个25-30 camelae。真圆锥花序不存在。膜锥壁（=锥鞘）是由一个内棱柱层，从第一隔膜的壁部分，和三个薄层，属于原介层。后一层的外部覆盖着原始喙的棱柱层。这表明外卷石和箭石在壳壁结构上存在显著差异。
The structure of pro-ostracum and primordial rostrum is presented at early ontogenic stages in Lower Jurassic belemnites temporarily assigned to ?Passaloteuthis from north-western Germany. For the first time the pro-ostracum was observed in the first camerae of the phragmocone. The presence of a pro-ostracum in early shell ontogeny supports Naef”s opinion (1922) that belemnites had an internal skeleton during their entire ontogeny, starting from the earliest post-hatching stages. This interpretation has been previously questioned by several writers. The outer and inner surfaces of the juvenile pro-ostracum were studied. The gross morphology of these surfaces is similar to that at adult ontogenetic stages. Median sections reveal that the pro-ostracum consists of three thin layers: an inner and an outer prismatic layer separated by a fine lamellar, predominantly organic layer. These layers extend from the dorsal side of the conotheca to the ventral side. The information obtained herein confirms the idea that the pro-ostracum represents a structure not present in the shell of ectocochleate cephalopods (Doguzhaeva, 1999, Doguzhaeva et al. 1999b, 2002a). The primordial rostrum surrounds the protoconch and continues as a distinct prismatic layer along the phragmocone, at least along the first 25-30 camerae. The conotheca proper is absent. The phragmocone wall (= conotheca) is composed of an inner prismatic layer that continues from the mural part of the first septum, and three thin layers, which belong to the pro-ostracum. The latter layers are externally covered by the prismatic layer of the primordial rostrum. This shows significant differences in the shell wall structure betwen ectocochleates and belemnites.