Ontogeny of the midgut gland of the spider crab Maja brachydactyla (Brachyura): morphology and ultrastructure

Abstract

The midgut gland, also called "hepatopancreas", is the most important digestive organ in decapods. The midgut gland of the spider crab Maja brachydactyla Balss, 1922 was studied in all larval (zoea I, zoea II and megalopa), first juvenile and adults stages employing stereo, light and electron microscopy techniques. The midgut gland is a massive organ that occupies the majority of the cephalotorax cavity, it is composed by blind-end tubules whose number increases from fourteen in the newly hatched larvae to tens of thousands in adults. During the larval development the length of the tubules increases significantly although their number is maintained constant. The tubules are lined by a simple and columnar microvillous epithelium that rest over a basal lamina, underlying the epithelium there is a thin connective and a network of muscle fibers. From hatching the midgut gland tubules are lined by an epithelium composed by five cell types with specialized roles: E-cells (embryonary) located in the tubule tips with mitotic and differentiation function, R-cells (resorptive) involved in nutrient storage and with apocrine secretory activity, F-cells (fibrillar) rich in mitochondria and Golgi bodies, B-cells (blister-like) characterized by a giant central vacuole that is released in the organ lumen, and M-cells (midget) with a tiny size but an unknown role