Morphological changes in the midgut, midgut gland and hindgut during the larval and postlarval development of the red king crab Paralithodes camtschaticus

Little alteration occurs in the midgut and hindgut during all zoea and in the early glaucothoe of Paralithodes camtschaticus, The gross morphology of the midgut gland is relatively simple. It is composed of one main and two secondary lobes. The anterior midgut caeca are present in the zoea and early glaucothoe, having histological characteristics similar to those found in the cells of the midgut gland lobes. On the contrary, the posterior caecum differentiated in the midgut of glaucothoe near the time of molting to the first juvenile. Large lipid droplets are accumulated during the zoeal instars in the medial portion of the midgut gland and anterior midgut caeca. A drastic change is observed in all digestive systems of the late phase of glaucothoe, The midgut maximally elongates and the anterior midgut caeca largely reduce. The posterior lobe elongates, extending up to the second and third abdominal segments. Most cells of the midgut gland of late glaucothoe decrease the previous Lipid droplets observed during the zoeal instars. It is proposed that these large amounts of lipids are used as an energy source during the non-feeding glaucothoe stage.