A STUDY OF THE ULTRASTRUCTURE AND ASSOCIATED ACID PHOSPHATASE ACTIVITY DURING DEVELOPMENT AND DIFFERENTIATION OF THE HEPATOPANCREATIC CELLS IN THE TERRESTRIAL ISOPOD, PORCELLIO SCABER (MOLT CYCLE, DISTAL CAP, VISCERAL MUSCLE)
The only structure of endodermal origin in the digestive system of terrestrial isopods is the hepatopancreas, a pair of bilobed structures, each connected to the digestive tract at the junction of the foregut and hindgut by a common hepatopancreatic duct. There are no remnants of the original midgut cells between the foregut and hindgut in Porcellio scaber confirming that the hepatopancreas is the only true midgut. The hepatopancreas, is regionally differentiated along its length from the blind-ended distal portion to its insertion into the cuticle-lined hepatopancreatic ducts. The distal tip is capped by a region of squamous cells, some of which contain myofilaments. Visceral muscle cells and their processes form a network of circular and longitudinal fibers surrounding the hepatopancreas along its length. In the adult intermolt hepatopancreas, typical S and B cell types first become evident in the early glandular region. Ultrastructural evidence points to secretion of digestive enzymes and absorption of nutrients as the role of the B cells. The absorptive S cells in the glandular region lack dictyosomes and extensive endoplasmic reticulum and function mainly in heavy metal storage. More proximally, the mature S cells appear to take on many of the characteristics of the B cells. During the other molting stages, the S cells with dictyosomes, dense secretory vesicles and rough endoplasmic reticulum may assume a more secretory function. The appearance and subsequent alteration in the hepatopancreas of such substances as lipids and copper are dependent on the molt cycle indicating cyclical accumulations of organic and inorganic reserves. The hepatopancreatic lobes are identical except for their growth pattern. The A lobes are considerably greater in size than the B lobes during the earliest stages of development. In comparison to the adult hepatopancreas, the only significant ultrastructural difference in these early stages is the presence of an intermediate cell type with characteristics of both S and B cells. Typical acid phosphatase accumulations are noted along the length of the gland indicating a role in intracellular digestion. Extracellular acid phosphatase activity confined to the lateral intercellular spaces in certain regions may play a part in the differentiation process.
BETTICA, ANNEMARIE, "A STUDY OF THE ULTRASTRUCTURE AND ASSOCIATED ACID PHOSPHATASE ACTIVITY DURING DEVELOPMENT AND DIFFERENTIATION OF THE HEPATOPANCREATIC CELLS IN THE TERRESTRIAL ISOPOD, PORCELLIO SCABER (MOLT CYCLE, DISTAL CAP, VISCERAL MUSCLE)" (1986). ETD Collection for Fordham University. AAI8615723.