Abstract
Sharks belong to the most primitive group of jawed vertebrates and have some special structural and functional features such as a cartilaginous skeleton, a spiral intestinal valve, and a rectal gland for osmoregulation. In January 2020, ten specimens of Galeus melastomus, the Blackmouth catshark, were collected from the Gulf of Asinara (North Sardinia, Italy) and the entire alimentary canal was studied using histochemical reactions to characterize the mucous cell types. In the alimentary canal of G. melastomus, mucous cells mainly secrete a mixture of acidic and neutral mucins. Of the acidic mucins, only the carboxylated type was present in mucous cells of the stomach, while the sulfated type predominated in the esophagus and the intestines. The use of lectins revealed a distribution of sugar residues in mucins related to cellular activities of the different regions of the catshark alimentary canal. The current study is the first report to characterize the intestinal mucous cells of G. melastomus and to provide quantitative data on their different populations in the alimentary canal.
Highlights
Sharks evolved about 400 million years ago, making them one of the oldest living jawed vertebrates [1,2]
Six main regions were distinguished in the alimentary canal of G. melostomus: Six main regions were distinguished in the alimentary canal of G. melostomus: esophaesophagus, stomach, ascending part of the stomach, proximal intestine, spiral intestine gus, stomach, ascending part of the stomach, proximal intestine, spiral intestine with spiral with spiral valve, and distal intestine valve, and distal intestine
This study of the alimentary canal of the Blackmouth catshark revealed that acidic mucins were more prevalent than neutral mucins
Summary
Sharks evolved about 400 million years ago, making them one of the oldest living jawed vertebrates [1,2]. The Blackmouth catshark (Galeus melastomus), a member of the family Scyliorhinidae, is widely distributed in the northeastern Atlantic Ocean and the western Mediterranean Sea, inhabiting the continental slope. It feeds mainly on bottom invertebrates including shrimps and cephalopods [5]. The stomach often is J-shaped, with a proximal descending and a distal ascending region [7]. According to Hart et al [1], the correct terms for the regions of shark intestines are proximal (not duodenum), spiral, and distal (not rectum). The most important region is the medially located spiral intestine with the spiral valve, which increases the absorptive surface area [7,8] and is found in other elasmobranchs (skates, rays, and sharks), lampreys [9], and other primitive fishes such as sturgeon [10,11]
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