软舌螺

✍ dations ◷ 2025-06-27 20:51:49 #软舌螺
软舌螺动物(学名:Hyolitha)是生活在古生代的一类神秘动物,具有小圆锥形的螺壳。这些物种目前都已全部灭绝;其化石一般只能保存锥壳、口盖和附肢三个部分,外壳为钙质成分,两侧对称。根据形态学的分类,本物种是一类海生有壳的无脊椎动物,但再具体一点的分类众说纷纭:近期以软组织化石分析发现软舌螺动物具有触手冠 (Lophophore) 这种进食器官,指出软舌螺动物其实应该独立为一门,而且和包含腕足动物门在内的触手冠动物 (Lophophorata) 较相近。软舌螺动物的碳酸钙质外壳很大可能是由霰石组成。 有口盖(英语:operculum)保护,还有两条又名海伦体的弯弯附肢(helens)去支撑身体,以边缘增生(英语:marginal accretion)的形式成长。 体长一般在一公分到四公分,横切面呈三角形或椭圆形。部分物种有环纹或条纹。原状壳具有带横向束微结构的内层和包含纵向束的外层。本物种的附肢叫作“海伦体”, Helens are long structures that taper as they logarithmically coil gently in a ventral direction.The helens were calcareous, with an organic component, and had an organic-rich central core surrounded by concentric laminae of calcite. They grew by the addition of new material at their base, on the cavity side, leaving growth lines. They were originally described by Walcott as separate fossils under the genus name Helenia, (Walcott's wife was named Helena and his daughter Helen); Bruce Runnegar adopted the name helen when they were recognized as part of the hyolith organism.口盖(英语:operculum)紧紧的把壳关闭。 The operculum closes perfectly over the aperture of the shell, leaving two gaps through which the helens can protrude.It comprises two parts: the cardinal shield, a flat region at the top of the shell; and the conical shield, the bottom part, which is more conical.The inside of the shell bears a number of protrusions, notably the dorsal cardinal processes and the radially-arranged clavicles.人们依据有无口唇将软舌螺动物门动物分成两个目:Hyolitha have dorso-ventrally differentiated opercula, with the ventral surface of the shell extending forwards to form a shelf termed the ligula.The Orthothecida are somewhat more problematic, and probably contain a number of non-hyoliths simply because they are so difficult to identify with confidence, especially if their operculum is absent.They have a straight (planar) opening, sometimes with a notch on the bottom side, and sealed with an operculum that has no ligula, clavicles, furrow or rooflets.Hyptiotheca is an unusual hyolithid, in that it lacks clavicles.Orthothecids fall into two groups: one, the orcothecida sensu stricto,is kidney or heart shaped in cross-section due to a longitudinal groove on its ventral surface, and its opercula bear cardinal processes; the other has a rounded cross-section and often lacks cardinal processes, making them difficult to distinguish from other cornet-shaped calcareous organisms.All were sessile and benthic; some may have been filter feeders.Because hyoliths are extinct and do not obviously resemble any extant group, it is unclear which living group they are most closely related to. They may be molluscs; authors who suggest that they deserve their own phylum do not comment on the position of this phylum in the tree of life.Their grade of organization is considered to be of the 'mollusc-annelid-sipunculid' level,consistent with a Lophotrochozoan affinity, and comparison is usually drawn with the molluscs or sipunculids.Older studies (predating the Lophotrochozoan concept) consider hyoliths to represent a stem lineage of the clade containing (Mollusca + Annelida + Arthropoda).软舌螺可能是底栖生物。 寒武纪软舌螺是全球分布,没有迹象显示有地区差异,有迹象显示软舌螺有长寿命浮游幼虫生活期;但在奥陶系不同的组合变得越来越普遍。最早的软舌螺壳体化石大约出现在5亿4000万年前的西伯利亚 Purella antiqua Zone 的Nemakit-Daldynian阶,其类似物发现于中国Paragloborilus subglobosus–Purella squamulosa Zone 的 梅树村阶(寒武纪第一个阶)。。软舌螺动物门物种无论在其数量及其多样性都在寒武纪达至巅峰,之后逐步递减,直到灭绝。

相关

  • 多多纳多多纳(多立克希腊语Δωδώνα, 爱奥尼亚希腊语:Δωδώνη, Dòdònè)是位于希腊西北部伊庇鲁斯的一个神谕处。虽然多多纳最早的铭文历史只能追溯至约公元前550-560年,但
  • 神经语言学神经语言学是人类大脑神经对于语言的理解,产出和习得之研究。作为一个跨学科领域,神经语言学运用了来自不同领域的方法,如神经科学、语言学、认知科学、神经生物学、沟通障碍、
  • 攀援始祖兽始祖兽(学名Eomaia)是一种已灭绝的哺乳动物,有可能是真兽下纲的最早祖先。始祖兽的化石是在中国辽宁的义县组发现,可追溯至下白垩纪的巴列姆阶。这个标本长10厘米及差不多完整,估
  • 水能水力发电(英文:Hydropower)是运用水的势能转换成电能的发电方式,其原理是利用水位的落差(势能)在重力作用下流动(动能),例如从河流或水库等高位水源引水流至较低位处,流的水流推动轮机
  • 巴黎圣母院《巴黎圣母院》(法語:Notre-Dame de Paris,港译钟楼驼侠,台译钟楼怪人)是法国文学家维克多·雨果所著、于1831年1月14日出版的小说。故事的场景设定在1482年的巴黎圣母院,内容环绕
  • 阿纳托利·叶夫根耶维奇·卡尔波夫阿纳托利·叶夫根耶维奇·卡尔波夫(俄语:Анатолий Евгеньевич Карпов,1951年5月23日-)是一位俄罗斯的国际象棋大师。 卡尔波夫生涯总共参加3,163场比赛,
  • 精是中医传统上所指的三宝之一,储存于脏腑里的肾脏之内,所谓“肾者主蛰,封藏之本,精之处也”。是人体所需能量来源,也就是“阴”。《素问·生气通天论》说:“因而强力,肾气乃伤。”
  • 四氢噻吩四氢噻吩(英语:Tetrahydrothiophene,缩写为THT)即“硫杂环戊烷”,分子式为 C 4
  • 鸟人《啼死鸟》(Birdman)是英国犯罪作家莫·海德(Mo Hayder) 的第一本小说。1999年发行,剧情是介绍了主角 DI Jack Caffery。续集是《治疗》(Treatment)。
  • 虢季子白盘虢季子白盘是西周时期的一件大型青铜器,中国国家一级文物,现收藏在中国国家博物馆。虢季子白盘在清道光年间出土于陕西宝鸡虢川司,后被时任陕西眉县县令徐燮占有,他离任后带回常