Metamorphosis in the Cirripede Crustacean Balanus amphitrite

Stalked and acorn barnacles (Cirripedia Thoracica) have a complex life cycle that includes a free-swimming nauplius larva, a cypris larva and a permanently attached sessile juvenile and adult barnacle. The barnacle cyprid is among the most highly specialized of marine invertebrate larvae and its settlement biology has been intensively studied. By contrast, surprisingly few papers have dealt with the critical series of metamorphic events from cementation of the cyprid to the substratum until the appearance of a suspension feeding juvenile. This metamorphosis is both ontogenetically complex and critical to the survival of the barnacle. Here we use video microscopy to present a timeline and description of morphological events from settled cyprid to juvenile barnacle in the model species Balanus amphitrite, representing an important step towards both a broader understanding of the settlement ecology of this species and a platform for studying the factors that control its metamorphosis. Metamorphosis in B. amphitrite involves a complex sequence of events: cementation, epidermis separation from the cypris cuticle, degeneration of cypris musculature, rotation of the thorax inside the mantle cavity, building of the juvenile musculature, contraction of antennular muscles, raising of the body, shedding of the cypris cuticle, shell plate and basis formation and, possibly, a further moult to become a suspension feeding barnacle. We compare these events with developmental information from other barnacle species and discuss them in the framework of barnacle settlement ecology.有柄藤壶与橡子藤壶（Cirripedia Thoracica）具有复杂的生命周期，包含自由游泳的无节幼体（nauplius larva）、腺介幼体（cypris larva），以及永久固着的幼体与成体藤壶。藤壶腺介幼体是海洋无脊椎动物幼虫中特化程度最高的类群之一，其附着生物学已得到广泛深入的研究。与之形成鲜明反差的是，鲜有研究聚焦于从腺介幼体黏附至附着基质（substratum）直至悬浮食性幼体出现的一系列关键变态发育事件。该变态过程不仅在个体发育层面极为复杂，同时对藤壶的存活至关重要。本研究借助视频显微镜技术，以模式物种纹藤壶（Balanus amphitrite）为研究对象，系统呈现了从附着腺介幼体到幼体藤壶的形态发育时序与事件细节。此项工作既为深入理解该物种的附着生态学提供了重要支撑，也为探究调控其变态发育的相关因素搭建了研究平台。纹藤壶的变态发育包含一系列复杂事件：腺介幼体黏附、表皮与腺介幼体外骨骼分离、腺介幼体肌肉系统降解、外套腔内胸部的旋转、幼体肌肉系统构建、触角肌收缩、躯体抬升、腺介幼体外骨骼脱落、壳板与基盘形成，以及可能的进一步蜕皮以成为悬浮食性藤壶。我们将这些发育事件与其他藤壶物种的发育研究结果进行对比，并围绕藤壶附着生态学的研究框架展开讨论。