Uyeno Theodore A, Kier William M
Department of Biology, University of North Carolina at Chapel Hill, CB #3280, Coker Hall, Chapel Hill, North Carolina, 27599 3280.
J Morphol. 2015 Apr;276(4):403-14. doi: 10.1002/jmor.20349. Epub 2014 Dec 15.
The arrangement of the musculature and the fibers of the extracellular matrix (ECM) in the flexible jaw joint of the sandworm Alitta virens (Annelida, Polychaeta) was studied using dissection and histology. The jaws are capable of a wide range of motions principally related to defense and feeding. The left and right jaws are embedded in and moved by a compact pharyngeal bulb of muscle and ECM that also forms the mouth and esophagus. Eight pharyngeal bulbs were removed and dissected to document gross anatomical features or preserved and embedded in plastic for sectioning in multiple planes. The sections were stained with toluidine blue and basic fuchsin to differentiate muscle and ECM. The sections were then digitized and used to develop a three-dimensional computer illustration. We hypothesize that the muscle and fibers in the ECM are arranged as a muscular hydrostat to support the movement of the jaws. Four specimens were recorded using a digital video camera and a tank with an angled mirror to record lateral and ventral views of jaw movements during locomotion and biting associated with burrow guarding and feeding. Frame by frame kinematic analysis of this video showed that the jaws move symmetrically in a roughly horizontal plane. Although the angle between the jaws increases and then decreases after maximum gape has been reached, the jaws also translate relative to each other such that the axis of rotation is not fixed. Together, these functional morphological and behavioral data identify the jaw mechanism as a flexible joint known as a muscle articulation. As muscle articulations have been previously described only in the beaks of cephalopods and flatworms, this study implies that this type of joint is more common and important than previously recognized.
利用解剖学和组织学方法，研究了沙蚕（Alitta virens，环节动物门，多毛纲）灵活的颚关节中肌肉组织和细胞外基质（ECM）纤维的排列方式。颚能够进行多种主要与防御和进食相关的运动。左右颚嵌入一个由肌肉和ECM组成的紧密咽球中，并由其驱动，该咽球还构成了口和食道。移除并解剖了八个咽球以记录大体解剖特征，或将其保存并包埋在塑料中以便在多个平面上切片。切片用甲苯胺蓝和碱性品红染色以区分肌肉和ECM。然后将切片数字化并用于制作三维计算机插图。我们推测，ECM中的肌肉和纤维排列成一个肌肉静水骨骼以支持颚的运动。使用数码摄像机和带有倾斜镜子的水槽记录了四个标本，以记录在运动以及与洞穴守卫和进食相关的咬食过程中颚运动的侧视图和腹视图。对该视频进行逐帧运动学分析表明，颚在大致水平的平面内对称移动。尽管在达到最大开口后颚之间的角度先增大然后减小，但颚也会相对彼此平移，使得旋转轴不固定。这些功能形态学和行为学数据共同确定颚的机制是一种称为肌肉关节的灵活关节。由于肌肉关节此前仅在头足类动物和扁虫的喙中被描述过，本研究表明这种类型的关节比之前认为的更为常见和重要。
