Brena Carlo, Cima Francesca, Burighel Paolo
Dipartimento di Biologia, Università di Padova, 35131 Padova, Italy.
J Morphol. 2003 Nov;258(2):225-38. doi: 10.1002/jmor.10145.
The alimentary tract of Kowalevskia tenuis and K. oceanica, the only species of the appendicularian family Kowalevskiidae, was studied both at the light and electron microscope levels and compared with species belonging to the other two families of the class. Kowalevskids show interesting specializations: 1) the pharynx opens on both sides through two opposing spiracles, modified into long ciliated fissures, and possesses an original filtering system of ciliated combs arranged in two pairs of opposing longitudinal rows; 2) the endostyle is absent, its place being taken by a ciliated groove without any glandular cell; 3) posterior to the esophagus, the globular stomach and rectum form a digestive nucleus comprising a few, large cells including two well-developed, specialized valves, cardiac and pyloric; 4) special apical junctions bearing characteristics of both gap and adherens junctions are diffuse along the gut epithelium; 5) the heart is absent. Our data suggest that Kowalevskiidae underwent a high degree of specialization for food filtering and are more closely related to Fritillariidae, with which they share several characters, rather than Oikopleuridae, the latter probably representing the most primitive family of appendicularians.
对 Kowalevskiidae 科仅有的两个物种——纤细 Kowalevskia 和海洋 Kowalevskia 的消化道进行了光学显微镜和电子显微镜水平的研究，并与该纲其他两个科的物种进行了比较。Kowalevskids 呈现出有趣的特化特征：1）咽通过两个相对的气门在两侧开口，气门演变成了长有纤毛的裂缝，并且拥有一个由两排相对的纵向排列的纤毛梳组成的独特过滤系统；2）内柱不存在，其位置被一个没有任何腺细胞的纤毛沟取代；3）在食管后方，球状胃和直肠形成一个消化核，由一些大细胞组成，包括两个发育良好的特殊瓣膜，贲门瓣和幽门瓣；4）具有间隙连接和黏着连接特征的特殊顶端连接沿肠道上皮扩散；5）心脏不存在。我们的数据表明，Kowalevskiidae 科在食物过滤方面经历了高度特化，并且与 Fritillariidae 科关系更密切，它们有几个共同特征，而不是与 Oikopleuridae 科关系密切，后者可能代表了最原始的尾海鞘纲家族。
