Embryonic shell formation in the snail Biomphalaria glabrata: a comparison between scanning electron microscopy (SEM) and synchrotron radiation micro computer tomography (SRµCT)

Abstract

Embryos of different developmental stages and newly hatched juveniles of the freshwater snail Biomphalaria glabrata were investigated by synchrotron radiation micro computer tomography (SRµCT). Because this method is sensitive for objects with a high X-ray density, it is ideally suited to study mineralized tissues without the need for dissection of the sample, i.e. removal of the soft tissue. This is a clear advantage over scanning electron microscopy (SEM). However, the resolution is inferior to SEM (about 1–2 µm compared to a few nm). After the measurement, computer-processed handling (virtual turning, cutting and measuring) of the object is possible. The development of the calcified shell in embryos before hatching (age 60, 72, 96 and 120 h after oviposition) was investigated and both methods were compared. While it was not possible to find a calcified shell in 60 h old embryos, the shell in 72 h old embryos was almost fully mineralized. By SRµCT, the weight of the calcified shell was estimated to 0.64, 9.59 and 30.3 µg for embryos of 72, 96 and 120 h. All juvenile snails, of 5 days and 4 weeks after hatching, contained concretions in the stomach, mostly consisting of calcium phosphate.