Distribution of Calcium and Chitin in the Tardigrade Feeding Apparatus in Relation to its Function and Morphology

• Published in: Integrative and comparative biology Vol. 55; no. 2; pp. 241 - 252
• Main Authors: Guidetti, Roberto, Alois Bonifacio, Tiziana Altiero, Roberto Bertolani, Lorena Rebecchi
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.08.2015; Oxford Publishing Limited (England)
• Subjects: Animals; aragonite; Biological Evolution; biomineralization; Calcium; Calcium - analysis; calcium carbonate; chemical composition; Chitin; Chitin - analysis; Chitinase; confocal laser scanning microscopy; energy-dispersive X-ray analysis; Feeding; Jaw - anatomy & histology; Jaw - chemistry; Jaw - physiology; Light microscopy; mechanical stress; Mineralization; Morphology; pharynx; Phylogenetics; Phylogeny; Predation; scanning electron microscopy; Soft Bodies, Hard Jaws: Phylogenetic Diversity of Prey Capture and Processing in Jawed, Soft-bodied Invertebrates; stylets; Tardigrada; Tardigrada - anatomy & histology; Tardigrada - chemistry; Tardigrada - physiology; X-ray spectroscopy
• ISSN: 1540-7063; 1557-7023; 1557-7023
• DOI: 10.1093/icb/icv008

The cuticular portion of the tardigrade feeding apparatus is a complex structure that can be schematically divided into four parts: a buccal ring, a buccal tube, a stylet system (formed by two piercing stylets, each within a stylet coat, and two stylet supports), and the lining of a myoepithelial sucking pharynx. To better understand the function and evolution of the feeding apparatus, the morpho-functional traits and chemical composition of the structures forming the feeding apparatuses of eight different species of tardigrades were analyzed. These eight species are representative of almost all main phylogenetic lineages of the phylum. The calcium and chitin in the feeding apparatus were examined by light microscopy, scanning electron microscopy, confocal laser scanning microscopy, energy dispersive X-ray spectroscopy, and Raman microspectroscopy (Raman). In all species, the feeding apparatus had been subjected to biomineralization due to CaCO ₃ encrustations organized in the crystalline form of aragonite. Aragonite and chitin are present in different concentrations in the feeding apparatus according to the structures and species considered. Generally, where the structures are rigid there is more aragonite than chitin, and vice versa. The buccal tube and piercing stylets are rich in calcium, with the piercing stylets apparently composed exclusively of aragonite. In eutardigrades, chitin is in higher concentration in the structures subject to higher mechanical stresses, such as the crests of the buccal crown and the condyles of the stylet furca.