Allen Justine J, Bell George R R, Kuzirian Alan M, Hanlon Roger T
Department of Neuroscience, Brown University, Providence, Rhode Island 02912, USA.
J Morphol. 2013 Jun;274(6):645-56. doi: 10.1002/jmor.20121. Epub 2013 Feb 2.
Coleoid cephalopods adaptively change their body patterns (color, contrast, locomotion, posture, and texture) for camouflage and signaling. Benthic octopuses and cuttlefish possess the capability, unique in the animal kingdom, to dramatically and quickly change their skin from smooth and flat to rugose and three-dimensional. The organs responsible for this physical change are the skin papillae, whose biomechanics have not been investigated. In this study, small dorsal papillae from cuttlefish (Sepia officinalis) were preserved in their retracted or extended state, and examined with a variety of histological techniques including brightfield, confocal, and scanning electron microscopy. Analyses revealed that papillae are composed of an extensive network of dermal erector muscles, some of which are arranged in concentric rings while others extend across each papilla's diameter. Like cephalopod arms, tentacles, and suckers, skin papillae appear to function as muscular hydrostats. The collective action of dermal erector muscles provides both movement and structural support in the absence of rigid supporting elements. Specifically, concentric circular dermal erector muscles near the papilla's base contract and push the overlying tissue upward and away from the mantle surface, while horizontally arranged dermal erector muscles pull the papilla's perimeter toward its center and determine its shape. Each papilla has a white tip, which is produced by structural light reflectors (leucophores and iridophores) that lie between the papilla's muscular core and the skin layer that contains the pigmented chromatophores. In extended papillae, the connective tissue layer appeared thinner above the papilla's apex than in surrounding areas. This result suggests that papilla extension might create tension in the overlying connective tissue and chromatophore layers, storing energy for elastic retraction. Numerous, thin subepidermal muscles form a meshwork between the chromatophore layer and the epidermis and putatively provide active papillary retraction.
头足纲软体动物会适应性地改变它们的身体图案（颜色、对比度、运动、姿势和纹理）以进行伪装和信号传递。底栖章鱼和乌贼拥有在动物界独一无二的能力，能够迅速且显著地将它们的皮肤从光滑扁平变为有皱纹的三维状态。负责这种物理变化的器官是皮肤乳头，其生物力学尚未得到研究。在本研究中，将乌贼（Sepia officinalis）的小型背部乳头保持在收缩或伸展状态，并使用包括明场、共聚焦和扫描电子显微镜在内的多种组织学技术进行检查。分析表明，乳头由广泛的真皮竖肌网络组成，其中一些呈同心圆排列，而另一些则横跨每个乳头的直径延伸。与头足纲动物的臂、触手和吸盘一样，皮肤乳头似乎起着肌肉静水骨骼的作用。真皮竖肌的协同作用在没有刚性支撑元件的情况下提供运动和结构支撑。具体而言，乳头基部附近的同心圆形真皮竖肌收缩并将覆盖组织向上推离外套膜表面，而水平排列的真皮竖肌将乳头周边拉向其中心并决定其形状。每个乳头都有一个白色尖端，这是由位于乳头肌肉核心与包含色素细胞的皮肤层之间的结构光反射器（白色素细胞和虹彩细胞）产生的。在伸展的乳头中，乳头顶端上方的结缔组织层似乎比周围区域更薄。这一结果表明，乳头伸展可能会在上覆的结缔组织和色素细胞层中产生张力，为弹性回缩储存能量。许多细小的表皮下肌肉在色素细胞层和表皮之间形成网络，并推测可提供主动的乳头回缩。
