Department of Biological Sciences, George Washington University, Washington, District of Columbia 20052, USA.
J Eukaryot Microbiol. 2012 Jul-Aug;59(4):407-22. doi: 10.1111/j.1550-7408.2012.00629.x. Epub 2012 May 31.
The first ultrastructural description of the genus Placus is presented. Each somatic kinetosome has a cone-shaped axosomal plate, nonoverlapping postciliary microtubules, an anteriorly directed kinetodesmal fiber, and a radial ribbon of transverse microtubules, which extend laterally under the ciliary furrow and insert in the cortical ridge. A closed ring of paired kinetosomes encircles the cytostome. A brosse begins adjacent to the oral pairs and extends posteriorly for one-fourth to one-half the cell's length. Autapomorphies for Placus include bowling pin-shaped toxicysts extruded onto a distinct area of the cell surface immediately posterior to the brosse, and a brosse kinety consisting of a single row of paired cilia. Placus and its sister taxon Spathidiopsis both have spiraling kineties composed of single cilia inserted into the side of the ciliary furrow. Spathidiopsis can be distinguished from Placus because it has a brosse consisting of two kineties (i.e. one composed of paired cilia, the other of single cilia), a row of rod-shaped toxicyst-bearing palps extending around one side of the oral area and along the length of the brosse, and a mid-cell cortical inpocketing containing toxicysts and a segment of the brosse. A revised listing of species assigned to the family Placidae is given.
现首次对 Placus 属进行超微结构描述。每个体动基体具有锥形轴体板、不重叠的后生亚纤微管、向前指向的动基体纤维和横向微管的放射状带，这些微管在纤毛沟的外侧横向延伸，并插入皮质脊中。一对动基体的封闭环环绕胞口。纤毛刷起始于口器对的相邻处，并向后延伸四分之一到一半细胞长度。Placus 的特有特征包括保龄球状的毒囊突显出现在纤毛刷后面的细胞表面的明显区域，以及由单排配对纤毛组成的纤毛刷联体。Placus 和它的姊妹分类群 Spathidiopsis 都具有螺旋状动基体，由插入纤毛沟侧面的单个纤毛组成。Spathidiopsis 可以与 Placus 区分开来，因为它具有由两个动基体组成的纤毛刷（即一个由配对纤毛组成，另一个由单个纤毛组成）、一排带有毒囊的杆状触须延伸到口器区域的一侧并沿着纤毛刷的长度、以及含有毒囊和纤毛刷部分的中部皮质内陷。给出了分配给 Placidae 科的物种修订清单。
