Functional morphology of the glandular esophageal pouches of chitons (Mollusca, Polyplacophora).

The esophageal pouches of Chaetopleura angulata and Acanthochitona fascicularis were investigated using light and transmission electron microscopy. These pouches linked to the posterior region of the esophagus are known as sugar glands as they contain a fluid rich in polysaccharide digesting enzymes. They are the second largest glands in the digestive system of chitons, just after the digestive gland. In both species, the pouches contain a dense array of finger-shaped villi. The villi epithelium includes absorptive cells, basophilic secretory cells, mucus-secreting cells, and basal cells. Some absorptive cells were bordered by a dense cover of long microvilli, whereas other absorptive cells had short and sparse microvilli. Absorptive cells contain several lysosomes, mitochondria, peroxisomes, a few small Golgi stacks, some lipid droplets, and large amounts of glycogen. The basophilic secretory cells are characterized by the presence of many electron-dense vesicles, with a glycoprotein content, a large number of rough endoplasmic reticulum cisternae, and a highly developed Golgi apparatus. Mucus-secreting cells are characterized by large vesicles containing acid polysaccharides and wide Golgi stacks. Basal cells that were found at the base of the epithelium in contact with the basal lamina exhibit histological and ultrastructural features of enteroendocrine cells. We suggest that these glandular pouches are involved in extracellular and intracellular digestion, and accumulate lipid and glycogen reserves.

Charge contrast imaging of biomaterials in a variable pressure scanning electron microscope.

Charge contrast imaging (CCI) is a dynamic phenomenon recently reported in insulating and semiconducting materials imaged with low vacuum or variable pressure scanning electron microscopes (SEM). Data presented in this paper illustrates that CCI can also be applied to biominerals and biological soft-tissues and that useful and unique structural information can be obtained from routine samples. Various resin-embedded samples were considered and example images from several different biomaterials are presented. Due to the diverse nature of samples that appear to exhibit charge contrast, this imaging technique has prospective application in a wide range of biological and biomedical research. This work represents the first application of CCI to biomaterials and in particular, highlights a new method for investigating the formation, structure and growth of biominerals.