title: Novel shell device for gas exchange in an operculate land snail.
abstract: The operculum of terrestrial snails tightly seals the shell aperture providing protection from predators and body-water loss. To allow respiration with a closed operculum, operculate land snails repeatedly evolved shell devices such as tubes or channels that open to the air. In all Asian members of the Alycaeidae, an externally closed tube lies along the suture behind the aperture that possesses a small internal opening into the last whorl at the tube's anterior end. However, this structure presents a paradox: how is gas exchanged through an externally closed tube? Here we show that many microtunnels open into the tube and run beneath radial ribs along the growth line of the last whorl in Alycaeus conformis These tunnels open to the outside of the shell surface near the umbilicus. Examination under high magnification revealed that the outermost shell layer forms these tunnels only in the whorl range beneath the sutural tube. Each tunnel (ca 16 µm diameter) is far narrower than any known metazoan parasite. These findings support our hypothesis that the externally closed sutural tube functions with microtunnels as a specialized apparatus for predator-free gas exchange with minimal water loss when the operculum seals the aperture.
authors.affiliation: Department of Biology, Shinshu University, Matsumoto 390-8621, Japan pallgergely2@gmail.com.
authors.forename: Barna
authors.identifier: 0000-0002-6167-7221
authors.initials: B
authors.lastname: Páll-Gergely
authors.affiliation: Life Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Fred
authors.initials: F
authors.lastname: Naggs
authors.affiliation: Department of Biology, Shinshu University, Matsumoto 390-8621, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Asami
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology* / Q000648:ultrastructure; D000818:Animals; D012908:Snails / Q000033:anatomy & histology* / Q000648:ultrastructure
keywords: Cyclophoroidea; Gastropoda; predator; shell morphology; sutural tube; water loss