Brachyuran crabs from diverse habitats show great differences in
their osmoregulatory processes, especially in terms of the structural
and physiological characteristics of the osmoregulatory organs. In
crustaceans, the antennal glands are known to be important in
osmoregulation, and they play a functional role analogous to that of
the vertebrate kidney. Nevertheless, the detailed structure and
function of the antennal glands in different species have rarely been
described. The aim of this study is to investigate the role of the
antennal gland in ion regulation by examining the ultrastructure of
the cells and the distribution of the ion regulatory proteins in each
cell type in the antennal gland of a semi-terrestrial crab. The results
showed that Na+
, K+
-ATPase activity significantly increased in the
antennal gland after a 4-day acclimation in dilute seawater and
returned to its original (day 0) level after 7 days. Three major types
of cells were identified in the antennal gland, including coelomic
cells (COEs), labyrinthine cells (LBRs) and end-labyrinthine cells
(ELBRs). The proximal tubular region (PT) and distal tubular region
(DT) of the antennal gland consist of LBRs and COEs, whereas the
end tubular region (ET) consists of all three types of cells, with fewer
COEs and more ELBRs. We found a non-uniform distribution of
NKA immunoreactivity, with increasing intensity from the proximal to
the distal regions of the antennal gland. We summarise our study
with a proposed model for the urine reprocessing pathway and the
role of each cell type or segment of the antennal gland.
