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首页> 外文期刊>Marine biology >How did phytoplankton-feeding larvae re-evolve within muricid gastropods? A view from developmental morphology
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How did phytoplankton-feeding larvae re-evolve within muricid gastropods? A view from developmental morphology

机译：浮游植物摄食的幼虫如何在鼠类腹足动物内重新进化？从发展形态学的观点

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Post-Paleozoic life history transitions in mollusks and echinoderms have been biased toward switches from feeding, planktonic larvae (planktotrophic), to one of the non-feeding developmental modes, such as maternally provisioned planktonic larvae, fully encapsulated larvae, or direct development. Nevertheless, rare resurrections of feeding larvae from fully encapsulated larvae have occurred within calyptraeid and muricid gastropods. The only previous study on the developing foregut of a muricid with encapsulated larvae (Nucella lapillus) indicated loss of the larval esophagus, a potential barrier to evolutionary re-emergence of larval planktotrophy. However, histological and ultrastructural examination of foregut development in two other nucellids, Nucella lamellosa and N. ostrina, both with fully encapsulated development, revealed a transient larval esophagus in both, as identified by anatomical position, tissue composition, interconnections to other structures, and fate at metamorphosis. The larval esophagus is difficult to recognize in nucellids without a comparative framework and a complete developmental series extending from early veliger stages through to juveniles. Both the larval mouth and distal larval esophagus are completely destroyed at metamorphosis. Surprisingly, encapsulated larvae of N. lamellosa also developed all three velar ciliary tracts needed for capture and ingestion of particles, despite absence of nurse egg feeding by encapsulated larvae of this species and despite apparent absence of phytoplankton-feeding larvae in this genus since its origin 20 million years ago. Retention of a larval esophagus and a full complement of velar ciliary tracts needed for particle capture and ingestion in encapsulated larvae of some muricids may help explain how larval planktotrophy re-emerged within this clade.
机译：软体动物和棘皮动物的古生代后生活史过渡已偏向于从摄食，浮游幼虫（浮游性）向非摄食发育模式之一转变，例如由母体提供的浮游幼虫，完全包裹的幼虫或直接发育。然而，在全覆膜幼虫和鼠形腹足动物中发生了从完全包囊的幼虫进食的幼虫罕见的复活。以前有关囊囊化幼虫（Nucella lapillus）的粘液虫的发育前肠的唯一先前研究表明，幼虫食道损失，这是幼虫浮游植物进化重新出现的潜在障碍。但是，组织学和超微结构检查的两个另外的核，前壳的Nucella lamellosa和猪N. ostrina的前肠发育，都被完全包封，通过解剖位置，组织组成，与其他结构的相互连接以及命运在变态。如果没有比较框架和完整的发育系列，从早期的食虫阶段一直到幼年期，幼虫食道很难在细胞核中识别。幼虫口和远端幼虫食道在变态时被完全破坏。出人意料的是，尽管没有该种类的包囊幼虫喂食哺乳卵，并且该物种自起源以来就明显缺乏以浮游植物为食的幼虫，但N. lamellosa的包囊幼虫也发育了捕获和摄取颗粒所需的所有三个丝状睫状道。两千万年前。保留幼虫食道和完整的绒毛睫状道，以捕获和摄取某些杀虫剂的包囊幼虫中的颗粒，可能有助于解释幼虫浮游生物如何在该进化枝中重新出现。

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    《Marine biology》 |2016年第1期|11.1-11.15|共15页
  • 作者

    Hookham Brenda; Page Louise R.;

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    Univ Victoria, Dept Biol, STN CSC, POB 1700, Victoria, BC V8W 2Y2, Canada;

    Univ Victoria, Dept Biol, STN CSC, POB 1700, Victoria, BC V8W 2Y2, Canada;

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