The loricate choanoflagellate genera Pleurasiga and Parvicorbicula are taxonomically ambiguous. Pleurasiga because of the uncertainty that relates to the true identity of the type species, and Parvicorbicula because too many newly described species over time have been dumped here in lack of better options. While all species currently allocated to the genus Pleurasiga (with the exception of the type species) are observed in our samples from the global warm water belt, the genus Parvicorbicula is represented by just a few and mostly infrequently recorded taxa. Two new species, viz. Pl. quadrangiella sp. nov. and Pl. minutissima sp. nov., are described here. While the former is closely related to Pl. echinocostata, the latter is reminiscent of Pl. minima. Core species of Pleurasiga and Parvicorbicula deviate from the vast majority of loricate choanoflagellates in having both the anterior and the mid-lorica transverse costae located exterior to the longitudinal costae. In Pl. quadrangiella there is no mid-lorica transverse costa but rather a small posterior transverse costa located inside the longitudinal costae. In Pl. minutissima the mid-lorica transverse costa has extensive costal strip overlaps which reveal patterns of costal strip junctions that deviate from the norm.

鞭毛鞭毛纲属Pleurasiga和Parvicorbicula在分类学上是模棱两可的。Pleurasiga是因为不确定性与类型物种的真实身份有关，而Parvicorbicula是因为随着时间的推移，太多新近描述的物种因缺乏更好的选择而被丢弃在这里。虽然在我们从全球温水带的样本中观察到了当前归入侧耳属属的所有物种（类型物种除外），但Parvicorbicula属仅代表了少数且很少记录的分类单元。两个新物种，即。Pl。夸瓜菌 十一月 和Pl。Minutissimasp。十一月。，这里描述。而前者与Pl密切相关。echinocostata，后者让人想起Pl。极小值。Pleurasiga和Parvicorbicula的核心物种与绝大部分的鞭毛鞭毛虫不同，其前侧和中侧眼前横肋均位于纵向肋的外侧。在Pl中。quadrangiella没有沿腰部肋骨横肋的肋骨，而是位于纵肋肋骨内侧的一小块后横肋肋骨。在Pl中。Minlorissima的中腰部横向肋缘具有广泛的肋缘交叠，这揭示了背离规范的肋缘交界处的模式。