Guadagnoli, J.A.*; Reiber, C.L.: The ontogeny of pericardial organs in the crayfish Procambarus clarkii

Adult crayfish pericardial organs, as in lobsters are described as emerging from the thoracic nerves and running toward the dorsal surface of the heart, becoming fine fibers that eventually take on a beaded form. Trunks emerge between the epimeral plate and spread over a large area of the membranous tissue lining the lateral pericardial wall and the tissue surrounding the heart ligaments. The PO are release sites for several neurohormones. The adult decapod heart is neurogenic, however it has been hypothesized that a developing embryo’s heartbeat is myogenic in origin only later becoming neurogenic. While neurogenic drive arises from the cardiac ganglion, the release of neurohormones from the PO provides additional regulation of heart function. The current study employed methylene blue staining techniques to determine the development of the PO in embryonic crayfish. The heart starts beating in the Nauplius 4 stage and is protruding posteriorly from its future location in the pericardial cavity. In juveniles the PO appear to be even more extensive that those found in adult crayfish. The PO is present during all three larval instars. At Nauplius 6 and 7, the PO appears to be extensive in the center and anterior portion of the dorsal carapace even though the heart at these stages is still protruding from the posterior end of the carapace. The PO is a site for release of serotonin. In the lobster, serotonin appears as early as 10% development, and has nearly its full complement of serotonergic fibers by 40-50% development. In other invertebrate systems, serotonin appears to play a role in regulating the pattern of development of neurons and their connections. The appearance of extensive PO during embryonic stages when the heart is still myogenic may imply an additional role for the PO during development.