Members of family Cymatiidae have an unusually long planktonic larval life stage (veligers) which allows them to be carried within ocean currents and become distributed worldwide. However, little is known about these planktonic veligers and identification of the larval state of many Cymatiidae is challenging at best. Here, we describe the first high-quality scanning electron microscopy images of the developing veliger larvae of Monoplex pilearis and Monoplex parthenopeus (Gastropoda: Cymatiidae). The developing shell of Monoplex veligers was captured by SEM, showing plates secreted to form the completed shell. The incubation time of the two species was recorded and found to be different; M. parthenopeus took 24 days to develop fully and hatch out of the egg capsules, whereas M. pilearis took over a month to leave the egg capsule. Using scanning electron microscopy and geometric morphometrics, the morphology of veliger larvae was compared. No significant differences were found between the shapes of the developing shell between the two species; however, it was found that M. pilearis was significantly larger than M. parthenopeus upon hatching. Although statistical analysis did not find morphological differences, this study concludes biological differences do exist between these two closely related species of Monoplex.

中文翻译：

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Monoplexpilaris 和 Monoplex parthenopeus (Gastropoda: Cymatiidae) 的早期发育：生物学和形态学

Cymatiidae 科的成员有一个异常长的浮游幼虫生命阶段（veligers），这使得它们能够被洋流携带并分布到世界各地。然而，对这些浮游植物知之甚少，而且鉴定许多 Cymatiidae 的幼虫状态充其量是具有挑战性的。在这里，我们描述了 Monoplex pilaris 和 Monoplex parthenopeus (Gastropoda: Cymatiidae) 发育中的 veliger 幼虫的第一张高质量扫描电子显微镜图像。Monoplex veligers 的发育壳被 SEM 捕获，显示出分泌的板以形成完整的壳。记录了两个物种的孵化时间，发现它们不同；M. parthenopeus 需要 24 天才能完全发育并从卵囊中孵化出来，而 M. pilearis 需要一个多月才能离开卵囊。使用扫描电子显微镜和几何形态测量学，比较了 veliger 幼虫的形态。两个物种之间发育的外壳形状之间没有发现显着差异; 然而，发现 M.pilaris 在孵化时明显大于 M. parthenopeus。虽然统计分析没有发现形态差异，但本研究得出结论，这两个密切相关的 Monoplex 物种之间确实存在生物学差异。