Microanatomy of the antennal glands and their Na+/K+-ATPase activity in three true crab species (Brachyura), Portunus pelagicus (Linnaeus, 1758) (Portunidae), Macrophthalmus dentipes Lucas in Guérin, 1836 (Macrophthalmidae) and Eriocheir hepuensis Dai, 1991 (Varunidae)

Abstract

There are differences between various crab species in the function and structure of organs involved in ionic and osmotic regulation processes. The antennal glands together constitute one of the most important organs involved in the osmoregulation in crabs. The present investigation aimed to study the tissue structure of the antennal glands and their Na+/K+-ATPase (NKA) pump activity in three true crab species from three different habitats, including the marine (Portunus pelagicus (Linnaeus, 1758)), the estuarine (Macrophthalmus dentipes Lucas in Guérin, 1836) and the freshwater habitat (Eriocheir hepuensis Dai, 1991). In this regard, the tissue structure of the antennal glands and the activity of the Na+/K+-ATPase (NKA) pump were assessed in these three selected species. The results showed that the antennal glands in all studied species consisted of two anterior parts and a posterior part. The anterior parts are composed of the proximal tubular region (PT) and the distal tubular region (DT). The PT and DT parts comprised the coelomosac and labyrinths in the anterior portion, and the bladder located in the posterior portion. However, despite the similarity in the general tissue structure of the antennal gland in marine, estuarine and freshwater crab species, some structural differences were observed between those species. Labyrinth cells, coelomosac podocytes, and bladder cells in the estuarine crab M. dentipes contained large vacuoles especially on the top (i.e., near the lumen) of the cells. The highest amount of NKA pump activity was measured in the antennal glands of M. dentipes (). The NKA pump plays a more important role in the estuary and seawater adaptation of crabs, but freshwater species are not highly dependent on the NKA enzyme for osmoregulation.

Evolution of ion transporter Na+/K+-ATPase expression in the osmoregulatory maxillary glands of an invasive copepod

“…We hypothesized that the maxillary glands serve as an essential component of the copepod ion regulatory system, specifically by reabsorbing ions from urine and then transporting the ions back to the hemolymph at low salinities. Crustacean maxillary glands have been hypothesized to serve as excretory organs 50 , 61 involved in urine production 62 , 63 , 64 based on morphological similarities (i.e., tubular structure and podocyte ultrastructure) with antennal glands of malacostracan crustaceans 37 , 65 , 66 , 67 and nephrons in vertebrate kidneys. 37 , 50 While the maxillary glands remain inadequately described, they consist of three main components: (1) the coelomic sac, where the initial filtration of hemolymph takes place, (2) the tubules, which are hypothesized to the be site of ion reabsorption, water exchange, and secretion of waste, and (3) the terminal excretory duct lined with a cuticle that opens at the base of the maxilla.…”