title: Distribution of Calcium and Chitin in the Tardigrade Feeding Apparatus in Relation to its Function and Morphology.
abstract: 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 CaCO3 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.
authors: *Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, 41124 Modena, Italy; roberto.guidetti@unimore.it.
authors: Roberto
authors: R
authors: Guidetti
authors: Department of Engineering and Architecture, University of Trieste, via Valerio 10, 34127 Trieste, Italy;
authors: Alois
authors: A
authors: Bonifacio
authors: Department of Education and Human Sciences, University of Modena and Reggio Emilia, viale Allegri 9, 42121 Reggio Emilia, Italy.
authors: Tiziana
authors: T
authors: Altiero
authors: Department of Education and Human Sciences, University of Modena and Reggio Emilia, viale Allegri 9, 42121 Reggio Emilia, Italy.
authors: Roberto
authors: R
authors: Bertolani
authors: *Department of Life Sciences, University of Modena and Reggio Emilia, via Campi 213/D, 41124 Modena, Italy;
authors: Lorena
authors: L
authors: Rebecchi
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002118:Calcium / Q000032:analysis; D002686:Chitin / Q000032:analysis; D007568:Jaw / Q000033:anatomy & histology / Q000737:chemistry / Q000502:physiology; D010802:Phylogeny; D058467:Tardigrada / Q000033:anatomy & histology / Q000737:chemistry* / Q000502:physiology*
chemical_list: D002686:Chitin; D002118:Calcium