Microlens arrays in the complex visual system of Cretaceous echinoderms

Abstract

It has long been assumed that photosensitivity in echinoderms is mainly related to diffuse photoreception mediated by photosensitive regions embedded within the dermis. Recent studies, however, have shown that some extant echinoderms may also display modified ossicles with microlenses acting as sophisticated photosensory organs. Thanks to their remarkable properties, these calcitic microlenses serve as an inspiration for scientists across various disciplines among which bio-inspired engineering. However, the evolutionary origins of these microlenses remain obscure. Here we provide microstructural evidence showing that analogous spherical calcitic lenses had been acquired in some brittle stars and starfish of Poland by the Late Cretaceous (Campanian, ~79 Ma). Specimens from Poland described here had a highly developed visual system similar to that of modern forms. We suggest that such an optimization of echinoderm skeletons for both mechanical and optical purposes reflects escalation-related adaptation to increased predation pressure during the so-called Mesozoic Marine Revolution.

Calcitic microlens arrays in Archaster typicus: microstructural evidence for an advanced photoreception system in modern starfish

“…At the present, detailed microstructural studies of analogous spherical calcitic lenses as an integral part of a photoreceptor system have been only reported in a few species of modern ophicomid brittlestars and starfish. Similar calcitic microlenses have been also observed in the Late Cretaceous (Campanian) fossil echinoderms (Gorzelak et al 2014). In this work, we report an evidence of analogous lens-like microstructures in a modern IndoPacific starfish Archaster typicus (Müller and Troschel 1840).…”

Tailoring Calcium Carbonate to Serve as Optical Functional Material: Examples from Biology and Materials Science

“…[14] The calcite hemisphere structures found in fossils are very similar to the lenses of modern forms. [14] Such calcite hemisphere structures within the skeletal construction of the dorsal arm plate have been reported in a few species of modern brittle stars and starfish. For example, a microlens system as part of the photoreceptor system was found on the dorsal arm plate of the brittlestar Ophiocoma wendtii, [2] as well as comparable structures, which also may be involved in a photoreceptor system of an extant species of the starfish Archaster typicus.…”

“…[14] Fossil echinoderms show a lenslike micro structure on the lateral arm plates and radial shields of Late Cretaceous starfishes and brittlestars. [14] Fossil echinoderms show a lenslike micro structure on the lateral arm plates and radial shields of Late Cretaceous starfishes and brittlestars.…”

“…[14] Fossil echinoderms show a lenslike micro structure on the lateral arm plates and radial shields of Late Cretaceous starfishes and brittlestars. [14] Such calcite hemisphere structures within the skeletal construction of the dorsal arm plate have been reported in a few species of modern brittle stars and starfish. [14] Such calcite hemisphere structures within the skeletal construction of the dorsal arm plate have been reported in a few species of modern brittle stars and starfish.…”

“…A recent study about calcite microlens arrays embedded in the dorsal arm plates in echinoderms suggest that a com plex photoreceptor system in echinoderms had been already acquired in the Late Cretaceous (Campanian and Maastrichtian, ≈ 72.1-66 Ma). [14] Fossil echinoderms show a lenslike micro structure on the lateral arm plates and radial shields of Late Cretaceous starfishes and brittlestars. [14] The calcite hemisphere structures found in fossils are very similar to the lenses of modern forms.…”