A set of possible sensory system preserved in cuticle of Late Devonian thylacocephalan arthropods from Poland

Abstract

The cuticle of concavicarids (Arthropoda: Thylacocephala) from the early Famennian (Upper Devonian) of the Holy Cross Mountains, Poland was studied with respect to its microstructural details. Investigated laminated cuticle with phosphatic/organic composition, possesses two different kinds of microstructure with assumed sensory functions. The first kind consists of circular depressions, each located in the central area of characteristic polygons forming the carapace exterior ornamentation. These depressions are interpreted as sealed during phosphatisation processes setal lumens. The second kind occurs exclusively in carapace margins. These intracuticular microstructures occur as elongated tubular structures, circular to oval in cross section, penetrating the cuticle interior but not reaching its surface. They form a thin belt with a kind of ‘sensory fields’ on the dorsum and a wider belt in the ventrocaudal part of the carapace. These belts are connected in the rostral and caudal area, forming a continuous sensory zone encompassing each valve. These structures are very similar to crustacean organule canals, and the dorsally situated ‘sensory fields’, suggest some similarity to crustacean sensory dorsal organs. This possible sensory system is the oldest of this kind found in Thylacocephala. Its morphology and presumed canal walls mineralogical composition suggests crustacean affinity of Thylacocephala.

Keywords:

• Famennian
• Kowala
• organule canals
• setae
• sensory organs
• Thylacocephala

Acknowledgements

The author extends enormous thanks to Ian Rolfe (Scotland) and to Joseph Kunkel (USA) for their corrections, comments and valuable discussion on every stages of the manuscript preparation. We also thank Michał Rakociński (Sosnowiec) for sharing with us his unpublished data on phosphorous content in the lower Famennian deposits of the Kowala quarry. The paper benefited from critical but constructive reviews from Jerzy Dzik (Warsaw) and Jean Vannier (Lyon), which are greatly acknowledged. Jerzy Dzik is additionally thanked for providing the photographs of the basal Famennian thylacocephalan cuticle from the Kowala quarry.