Center of Natural History (CeNak), Universität Hamburg, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany.
Functional Morphology and Biomechanics, Zoological Institute of the Christian Albrecht Universität zu Kiel, Am Botanischen Garten 9, 24118 Kiel, Germany.
Zoology (Jena). 2019 Dec;137:125713. doi: 10.1016/j.zool.2019.125713. Epub 2019 Oct 21.
One important autapomorphy of molluscs is the radula, which is the anatomical structure used for feeding in most species of Mollusca. As this phylum represents the second species-richest animal group inhabiting very diverse environments, it is not surprising that the morphology of the radula and its teeth is also very diverse between taxa. However, the taenioglossan radulae are remarkable because its tooth types (central, lateral, and marginal teeth) are highly distinct in their morphology within the same radula. There are several hypotheses attempting to explain this tooth diversity by their functional specialisations. Here, for the first time, the functional morphology of taenioglossan radular teeth from one single species was analysed and their material properties (hardness and elasticity modulus) were characterised by nanoindentation. Spekia zonata Bourguignat, 1879 belongs to the Paludomidae inhabiting and feeding on solid substrates in Lake Tanganyika. All tooth types show gradual and significant differences in their stiffness and hardness: from the basis, as the softest and most flexible area, to the stylus and the cusps as the stiffest and hardest areas. The flexibility of the stylus allows the teeth to act as one single feeding organ: the central and lateral teeth can stabilize each other during feeding by the rear teeth providing support to the next row. Tooth types also differ significantly in their stiffness and hardness: the central teeth consist of the hardest and stiffest material, followed by the lateral teeth and finally marginal teeth. This can be explained by different functional loads of teeth: central and lateral ones are used for scratching over the substrate while the marginals serve mainly as brooms collecting food particles.
软体动物的一个重要的独特特征是齿舌，这是大多数软体动物物种用于进食的解剖结构。由于这个门是栖息在非常多样化环境中的第二大物种丰富的动物群，齿舌及其牙齿的形态在不同分类群之间也非常多样化也就不足为奇了。然而，有沟贝类的齿舌是显著的，因为它的牙齿类型（中央齿、侧齿和缘齿）在同一齿舌内形态上高度不同。有几个假说试图通过它们的功能特化来解释这种牙齿多样性。在这里，首次对来自单一物种的有沟贝类齿舌的功能形态进行了分析，并通过纳米压痕法对其材料特性（硬度和弹性模量）进行了表征。Spekia zonata Bourguignat, 1879 属于 Paludomidae 科，栖息在坦噶尼喀湖的固体基质上并以其为食。所有的牙齿类型在刚度和硬度上都表现出逐渐和显著的差异：从基部，作为最柔软和最灵活的区域，到柱体和齿尖作为最坚硬和最硬的区域。柱体的灵活性使牙齿能够作为一个单一的进食器官发挥作用：在进食过程中，后牙为下一行提供支撑，从而使中央齿和侧齿相互稳定。牙齿类型在刚度和硬度上也有显著差异：中央齿由最坚硬和最硬的材料组成，其次是侧齿，最后是缘齿。这可以用牙齿的不同功能负荷来解释：中央齿和侧齿用于在基质上刮擦，而缘齿主要用作收集食物颗粒的扫帚。
