Hairy and iridescent chaetae of the sea mouse Aphrodita (Annelida, Errantia)

Abstract

The bright iridescent chaetae of Aphrodita species have fascinated scientists for decades. The particular nanoscale substructure of these chitinous bristles resembles photonic crystals and manipulates the incident light in a way that results in spectacular structural coloration. Even though Aphrodita's chaetae have garnered great attention from the field of biomimetics, the few previous ultrastructural studies primarily focused on acicular chaetae that are much less iridescent than the thin capillary notochaetae. In this paper, we present new ultrastructural data on the chaetae of two species of Aphrodita and illustrate their formation process. Our results allow us to specify the prerequisite for iridescent chaetae. Aphrodita species are dorsally covered with a matted felt of intertwined chaetae, and we further discuss the evolution of feltage chaetae in Aphroditiformia. In addition to iridescent feltage chaetae, we also provide new insights into the chaeotogenesis of pilose chaetae. For the first time, our study shows that the hairy tips and ornamentation of the chaetae is formed by follicle cells alone and thus attribute a further role to this type of cells.

Dynamic microvilli sculpt bristles at nanometric scale

“…By contrast, the chaetoblast-specific expression of cs3 , and the observed similarity of cs3 crispants with the phenotype obtained by general inhibition of chitin synthases—combined with the localisation of chitin synthases to tips of microvilli in the insect gut 27 , 28 , and the recent validation that chitin synthases act as transmembrane proteins capable of directional synthesis 19 —collectively rather support the alternative model in which the chaetoblast works like the biological correlate of a 3D printer relying on a material jetting principle 10 . Our findings do not contradict the role of the follicle cells in additional chitin synthesis, in the secretion of enamel or in the ornamentation of bristles, as has been suggested in nereidid worms and different polychaete groups 9 , 29 . Our model also reinforces fundamental differences in the processes underlying the formation of fly bristles: Chaetoblasts sculpt extracellular beta-chitin objects, whereas fly bristles are specifically shaped cells coated by an alpha-chitin cuticle 4 , 28 , 30 .…”

Hooked on zombie worms? Genetic blueprints of bristle formation in Osedax japonicus (Annelida)

“…Specifically, in fully formed chaetae, NF70 was observed to be expressed in the apical-most (third) follicle cell. This finding aligns with the previous ultrastructural studies, which have shown that follicle cells, often laden with intermediate filaments, play a crucial role in attaching and stabilizing the chaeta within the follicle [9,11].…”

“…Moreover, in some scale worms, like Sthenelais berkeleyi, chaetae can even play a key role in respiration [ 8 ]. The iridescence of the sea mouse's ( Aphrodita ) bristles have intrigued researchers in fields from structural coloration to bio-inspired design and exemplifies the functional and morphological versatility of chaetae, likened to glass fibers in their physical properties [ 9 , 10 ].…”

A micromorphological analysis of Bolonia lata Meunier from the Cretaceous of the Neuquén Basin (Patagonia, Argentina): new insights into the tracemaker

“…The rest of the body shows hair‐like, iridescent bristles, except for a ventral hairless zone (Schäfer 1972; Tilic et al . 2022, fig. 1b).…”