Origin of Germ Cells and Early Differentiation of Gonads in the Starfish, Asterina pectinifera. (starfish/germ cells/PGC/gonad/haemal sinus)

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Abstract
The origin of the germ cells and the development of the genital system in the annually spawning starfish, Asterina pectinifera, were studied by light and electron microscopy. Characteristic germ cells were first characterized in gonads after spawning: the gonia are larger than somatic cells, have large nuclei (with electron-lucent nucleoplasm), and show mitochondrial aggregation associated with nuage (electron-dense bodies). In young starfish without gonads similar cells were detected in the haemal sinus, where they were termed primordial germ cells (PGCs). Brachiolariae and metamorphosed juveniles had a cellular cluster in the coelomic epithelium, near the hydroporic canal. The cluster was comprised of cells endowed with the above-mentioned characteristics of the germ cells. The germ cell counts indicated that PGCs migrate from the aboral haemal sinus near the hydroporic canal, through the haemal sinus to the gonads, where they settle, proliferate, and differentiate into gonia.