Baer Alexander, Mayer Georg
Animal Evolution and Development, Institute of Biology, University of Leipzig, Talstrasse 33, D-04103 Leipzig, Germany.
J Morphol. 2012 Oct;273(10):1079-88. doi: 10.1002/jmor.20044. Epub 2012 Jun 18.
Onychophorans use a unique hunting and defense strategy, which involves the ejection of an adhesive slime secretion produced by a pair of specialized glands. So far, a comparative study on the anatomy of these glands has not been carried out among different species. In this article, we compare anatomical features of slime glands in representatives of two major onychophoran subgroups, the Peripatopsidae and the Peripatidae, from different parts of the world. Our data show that the musculature of the reservoir is conserved whereas the composition of the secretory duct displays taxon-specific variation. Major differences concern the arrangement of glandular endpieces, which are distributed along the duct in Peripatopsidae but condensed in numerous repeated rosettes in Peripatidae. In addition, there are differences in the attachment pattern of slime glands to the inner surface of the body wall and to the outer surface of the gut between the two major onychophoran subgroups. A tube-like structure with a putative valve-like function is found at the transition of the secretory duct and the reservoir in the five Peripatopsidae species studied whereas it is absent in the two representatives of Peripatidae. Our findings suggest that the arrangement of musculature in the reservoir of the slime gland has remained unchanged since the divergence of Peripatidae and Peripatopsidae, while the composition of the secretory duct has been altered in one of these groups. However, the direction of evolutionary changes in duct composition cannot be determined unambiguously due to current uncertainty regarding the phylogenetic relationships of Onychophora.
栉蚕采用独特的捕猎和防御策略，该策略涉及排出由一对特殊腺体产生的粘性黏液分泌物。到目前为止，尚未在不同物种之间对这些腺体的解剖结构进行比较研究。在本文中，我们比较了来自世界不同地区的栉蚕两个主要亚群（南栉蚕科和栉蚕科）代表的黏液腺解剖特征。我们的数据表明，储液囊的肌肉组织是保守的，而分泌导管的组成显示出特定分类群的变异。主要差异在于腺末段的排列，在南栉蚕科中腺末段沿导管分布，而在栉蚕科中则浓缩成许多重复的玫瑰花结。此外，在这两个主要的栉蚕亚群之间，黏液腺与体壁内表面和肠道外表面的附着模式也存在差异。在所研究的五个南栉蚕科物种中，在分泌导管和储液囊的过渡处发现了一种具有假定瓣膜功能的管状结构，而在栉蚕科的两个代表物种中则不存在。我们的研究结果表明，自栉蚕科和南栉蚕科分化以来，黏液腺储液囊中的肌肉组织排列保持不变，而其中一个类群的分泌导管组成发生了改变。然而，由于目前栉蚕系统发育关系的不确定性，分泌导管组成的进化变化方向无法明确确定。
