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Ontogenetic dynamics of the subepidermal spicule complex in Nudibranchia (Gastropoda): the case of Onchidoris muricata
Zoology ( IF 2 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.zool.2020.125886
Ekaterina Nikitenko 1 , Alexander Ereskovsky 2 , Elena Vortsepneva 1
Affiliation  

Spicules are mineral-based biocomposites skeletal structures that are widely distributed among phylogenetically distant groups of invertebrates (Porifera, Cnidaria, Mollusca, Echinodermata). Subepidermal spicules are formed under the ectodermal epithelium and are characterized for all groups except mollusks (Aplacophora, Polyplacophora, Bivalvia), their spicules are located on the surface of the body. However, one group of mollusks (Gastropoda: Heterobranchia) have unique subepidermal spicules that have never been detected above the ectodermal epithelium and similarly to those characterized for Porifera, Cnidaria and Echinodermata. Understanding subepidermal spicule formation in mollusks could help solve the question on the origin of spicules. Spicules in nudibranchs have been described for more than 150 years, yet ontogenetic dynamics of spicules have never been studied and the full mechanism of their formation remains unknown. Herein we investigate the spicule formation in different stages of postlarval development of the nudibranch Onchidoris muricata (O.F. Müller, 1776). For the first time, ontogenetic transformations of the spicule complex are described using experiments and different morphological methods. Our studies demonstrate that spicules of O. muricata form in the subepidermal space in early developmental stages immediately after veliger settlement. A single spicule forms inside a huge vacuole within a sclerocyte and remains there throughout the entire life of the specimen. Signs of spicule or sclerocyte migration under the epithelium in postlarval development was not found. Spicules only form during larval settlement, increasing only in size as development furthers. For the first time, spicule mineralization zones were detected at the tips of the spicules as well as the presence of collagen I in the overall composition of the spicules. Thus, our findings suggest that spicules form by an ectodermal cell that emerged under the ectodermal epithelium during the earliest stages of postlarval development.

中文翻译:

裸鳃亚目(腹足纲)表皮下针复合体的个体发生动力学:以 Onchidoris muricata 为例

骨针是基于矿物的生物复合材料骨骼结构,广泛分布在系统发育上相距遥远的无脊椎动物群(Porifera、刺胞动物、软体动物、棘皮动物)中。表皮下针状体在外胚层上皮下形成,其特征是除软体动物(Aplacophora、Polyplacophora、Bivalvia)外的所有类群,它们的针状体位于身体表面。然而,一组软体动物(腹足纲:异鳃类动物)具有独特的表皮下针状体,从未在外胚层上皮上方检测到这些针状体,并且与多孔虫、刺胞动物和棘皮动物的特征相似。了解软体动物表皮下针刺的形成有助于解决针刺起源的问题。裸鳃类动物的骨针已被描述超过 150 年,然而,针状体的个体发生动力学从未被研究过,其形成的完整机制仍然未知。在此,我们研究了裸鳃类 Onchidoris muricata (OF Müller, 1776) 在后期幼体发育的不同阶段的针刺形成。首次使用实验和不同的形态学方法描述了针状复合体的个体遗传转化。我们的研究表明 O. muricata 的针状体在 veliger 定居后立即在早期发育阶段的表皮下空间中形成。单个骨针形成在硬化细胞内的巨大液泡内,并在标本的整个生命周期内都留在那里。未发现后期幼体发育过程中上皮下的骨刺或硬核细胞迁移迹象。针状体仅在幼虫沉降期间形成,随着发展的进一步发展,规模只会增加。首次在针状体的尖端检测到针状体矿化区,并在针状体的整体组成中检测到胶原蛋白 I 的存在。因此,我们的研究结果表明,在后期幼体发育的最早阶段,针状体是由外胚层上皮下出现的外胚层细胞形成的。
更新日期:2021-02-01
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