Misaki Marine Biological Station, School of Science, The University of Tokyo, Miura, Japan.
Yokohama Hakkeijima Sea Paradise, Yokohama, Japan.
J Morphol. 2022 Feb;283(2):149-163. doi: 10.1002/jmor.21434. Epub 2021 Dec 11.
Cephalopods have acquired numerous novelties and expanded their habitats to various marine environments as highly agile predators. Among cephalopod novelties, multiple arms are used for complex behaviors, including prey capture. Suckers on arms are innovative features for realizing these arm functions. In addition, tentacles in Decapodiformes (squids and cuttlefishes) are arms specialized in prey capture and tentacular suckers show unique morphologies. However, little is known about the developmental process of sucker formation that should differ between tentacles and other arms. In this study, therefore, sucker formation processes on second arms and tentacles were observed and compared in a bigfin reef squid, Sepioteuthis lessoniana, to reveal the developmental processes forming the unique sucker morphologies, especially in tentacles. Morphological and histological observations of suckers during embryogenesis showed that, in second arms, the sucker-producing area appeared at the most distal part. At the most proximal side of the sucker-producing area, new sucker buds were isolated by invagination of the epithelial tissue. At the proximal arm parts, suckers with functional structures were observed. In tentacles, although the basic sucker formation pattern was similar to that in second arms, sucker formation started at earlier embryonic stages and the number of suckers was drastically increased compared to that in second arms. In addition, although four sucker rows were observed at the tentacular club, that is, the thickest part of a tentacle, our observations suggested that two sets of two sucker rows are compressed to form the four rows. Therefore, the sucker-formation processes are temporally and spatially different between arms and tentacles. In addition, S. lessoniana shows conserved and unique patterns of sucker formation in comparison with previously described species, suggesting that sucker formation patterns were diversified among Decapodiformes lineages.
头足类动物是高度灵活的掠食者，它们通过获得众多新特征并扩展其栖息地来适应各种海洋环境。在头足类动物的新特征中，多条腕用于实现复杂行为，包括捕食。腕上的吸盘是实现这些腕功能的创新特征。此外，十足目（鱿鱼和乌贼）的触手是专门用于捕食的腕，其吸盘具有独特的形态。然而，对于吸盘形成过程知之甚少，该过程在触手和其他腕之间应该有所不同。因此，本研究观察并比较了大鳍鱿鱼 Sepioteuthis lessoniana 第二腕和触手的吸盘形成过程，以揭示形成独特吸盘形态的发育过程，尤其是在触手。胚胎发生过程中吸盘的形态和组织学观察表明，在第二腕中，吸盘产生区域出现在最远端。在吸盘产生区域的最近端，上皮组织的内陷将新的吸盘芽分隔开。在近腕部，观察到具有功能结构的吸盘。在触手，尽管基本的吸盘形成模式与第二腕相似，但吸盘的形成始于更早的胚胎阶段，并且与第二腕相比，吸盘的数量急剧增加。此外，尽管在触手的触腕（即触手最厚的部分）上观察到了四排吸盘，但我们的观察表明，两排两个吸盘被压缩形成四排。因此，吸盘的形成过程在时间和空间上在腕和触手之间是不同的。此外，与以前描述的物种相比，S. lessoniana 的吸盘形成模式具有保守和独特的特征，表明在十足目谱系中，吸盘形成模式多样化。
