Mayer Georg, Oliveira Ivo S, Baer Alexander, Hammel Jörg U, Gallant James, Hochberg Rick
*Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany; Animal Evolution and Development, Institute of Biology, University of Leipzig, D-04103 Leipzig, Germany;
Animal Evolution and Development, Institute of Biology, University of Leipzig, D-04103 Leipzig, Germany;
Integr Comp Biol. 2015 Aug;55(2):217-27. doi: 10.1093/icb/icv004. Epub 2015 Mar 30.
Onychophorans are carnivorous, terrestrial invertebrates that occur in tropical and temperate forests of the Southern Hemisphere and around the Equator. Together with tardigrades, onychophorans are regarded as one of the closest relatives of arthropods. One of the most peculiar features of onychophorans is their hunting and feeding behavior. These animals secrete a sticky slime, which is ejected via a pair of slime-papillae, to entangle the prey. After the prey has been immobilized, its cuticle is punctured using a pair of jaws located within the mouth. These jaws constitute internalized appendages of the second body segment and are innervated by the deutocerebrum; thus, they are homologous to the chelicerae of chelicerates, and to the (first) antennae of myriapods, crustaceans, and insects. The jaws are also serial homologs of the paired claws associated with each walking limb of the trunk. The structure of the jaws is similar in representatives of the two major onychophoran subgroups, the Peripatidae and Peripatopsidae. Each jaw is characterized by an outer and an inner blade; while the outer blade consists only of a large principal tooth and up to three accessory teeth, the inner blade bears numerous additional denticles. These denticles are separated from the remaining part of the inner jaw by a diastema and a soft membrane only in peripatids. The onychophoran jaws are associated with large apodemes and specialized muscles that enable their movement. In contrast to the mandibles of arthropods, the onychophoran jaws are moved along, rather than perpendicular to, the main axis of the body. Our elemental analysis reveals an increased incorporation of calcium at the tip of each blade, which might provide rigidity, whereas there is no evidence for incorporation of metal or prominent mineralization. Stability of the jaw might be further facilitated by the cone-in-cone organization of its cuticle, as each blade consists of several stacked, cuticular elements. In this work, we summarize current knowledge on the jaws of onychophorans, which are a characteristic feature of these animals.
栉蚕是肉食性陆生无脊椎动物，分布于南半球的热带和温带森林以及赤道附近。栉蚕与缓步动物一起被视为节肢动物最亲近的亲属之一。栉蚕最独特的特征之一是它们的捕猎和进食行为。这些动物会分泌一种粘性黏液，通过一对黏液乳头喷出，以缠住猎物。猎物被固定后，用位于口腔内的一对颚刺穿其角质层。这些颚构成第二体节的内化附肢，并由中脑支配；因此，它们与螯肢动物的螯肢、多足纲动物、甲壳类动物和昆虫的（第一）触角同源。这些颚也是与躯干每个步足相关的成对爪子的连续同源物。在栉蚕的两个主要亚群，即栉蚕科和南栉蚕科的代表中，颚的结构相似。每个颚的特征是有一个外刀片和一个内刀片；外刀片仅由一个大的主齿和多达三个副齿组成，而内刀片有许多额外的小齿。只有在栉蚕科中，这些小齿通过一条间隙和一层软膜与内颚的其余部分隔开。栉蚕的颚与大型的表皮内突和专门的肌肉相连，使其能够运动。与节肢动物的下颚不同，栉蚕的颚是沿着身体的主轴移动，而不是垂直于主轴移动。我们的元素分析表明，每个刀片尖端的钙含量增加，这可能提供了刚性，而没有证据表明有金属掺入或明显的矿化。颚的稳定性可能会因角质层的锥套结构而进一步提高，因为每个刀片都由几个堆叠的角质层元素组成。在这项工作中，我们总结了目前关于栉蚕颚的知识，这是这些动物的一个特征。
