Characterization of tongue worm (Pentastomida) chitin supports α- rather than β-chitin

Abstract

The higher order relationships of the Pentastomida have historically been tenuous. In one early and influential study, analysis of extracted chitin implicated that pentastomids possess β-chitin, a paradoxical finding given that the α allomorph is found uniformly in the cuticles of all arthropods and is considered as an apomorphic character of the Ecdysozoa. This result was further used to support the idea that the enigmatic pentastomids might be a wholly independent clade. More recent studies, however, firmly place the pentastomids within the Ecdysozoa, suggesting that the state of its chitin should be re-examined. In this study, we extracted high-quality chitin from the pentastomid, Leiperia cincinnalis, and carried out diagnostic analyses. Fourier Transform Infrared Spectroscopy (FT-IR) and ThermoGravimetric Analysis (TGA) demonstrated the conspicuous features of α-chitin but not β-chitin. Furthermore, transmission electron microscopy (TEM) of the cuticle of the anterior part of a specimen revealed nanofibres organized largely in a parallel configuration and scanning electron microscopy (SEM) of isolated cuticular chitin exhibited well-defined chitin bundles, these observations being more consistent with the known characteristics of α-chitin. Collectively, our analyses demonstrate the clear existence of α-chitin in a pentastomid and clarify a contentious issue using modern methods of analysis.