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Summary
The large Lucinidae Lucina pectinata (Gmelin) is a dominant species in the most confined areas of mangrove swamps where it lives deeply burrowed in reducing mud. In most female individuals, the gonads of this protandric species are in an apparently permanent state of maturity, having a various proportion of small previtellogenic oocytes together with larger oocytes undergoing vitellogenesis and full-grown oocytes which are characterized by their thick jelly coat. Oocyte resorption is also frequent in these gonads. Such a maturation schedule results in a continuous reproductive competence. Resorption of spermatozoa and simultaneous oogonia multiplication take place in spent male gonads allowing for a progressive sex change. In spent and developing stages, gonad-wall cells constitute a thick pseudo-stratified epithelium which gets progressively thinner with gonad maturation and thickens again soon after spawning. The complex cycle of these follicular cells is the result of two complementary functions: storage of lipid, protein and carbohydrate compounds ready for transfer to maturing oocytes, and resorption of degenerating oocytes through a peculiar lysosomal activity, demonstrated by cytoenzymological identification. Having permanently mature gonads ready for spawning is a reproductive strategy of L. pectinata which, in addition to gill sulfur-oxidizing bacterial endosymbionts and high bacteriocyte hemoglobin concentration, is adapted to the high-stress environment of mangrove swamps. Resorption of oocytes and recovery of metabolites through the follicular cell lysosomal function appears to be the most efficient means to minimize the metabolic cost of maintaining a permanent state of maturity.
