Fine Structure of the Crayfish Sinus Gland

The sinus gland of the crayfish, Procambarus clarkii, is located on the dorsum of the eyestalk, just beneath the exoskeleton and adjacent to the medullae interna and externa optic ganglia. It functions to secrete a variety of proteinaceous hormones, including the erythrophore concentrating hormone, melanophore dispersing hormone, molt inhibiting hormone, diabetogenic hormone, distal retinal pigment hormone, and ovary inhibiting hormone.The gland is composed of numerous neurosecretory axon terminals clustered about a branching blood sinus. The neurosecretory axons arise from cells lying some distance away from the sinus gland, in the medulla terminal is X-organ, the brain, and possibly the thoracic ganglion. The hormones are manufactured in the perikarya of these cells and transported through the axons to their terminals in the sinus gland for storage and release into the blood sinus.Small, electron dense spherules within the axons contain the hormone secretory product. These neurosecretory granules are very similar in morphology to those reported in the sinus glands of the dwarf crayfish, Cambarellus shufeldti, the land crab, Gecarcinus lateralis, and the Mediterranean isopod, Sguilla mantis. The sinus glands of each of these crustaceans contain two size ranges of neurosecretory granules: 1500-2000A and 500-900A.