UNUSUAL MODES OF OOGENESIS AND BROODING IN BIVALVES: THE CASE OF GAIMARDIA TRAPESINA (MOLLUSCA: GAIMARDIIDAE)

ITUARTE, C.

INVERTEBRATE BIOLOGY

Willey

Año: 2009 vol. 128 p. 243 - 251

1077-8306

Follicular oogenesis in Gaimardia trapesina, a common brooding marine bivalve from the Magellan Region and adjacent Sub Antarctic waters, is reported. The gonad of G. trapesina is an acinus organ infiltrated in the perivisceral connective tissue; the walls of the acini are formed by tall, slender cylindrical cells with distal nuclei, supported by a thin conjunctive tissue layer. Oogenesis in G. trapesina is atypical for bivalves, being of the follicular type. Just at the onset of vitellogenesis, each developing oocyte is surrounded by a one-cell-thick layer of follicle cells (FCs), forming a follicle that completely encompass single oocytes, except at the basal zone where oocytes are in contact with the acinus wall. The follicle persists up to the end of vitellogenesis. After the gamete release, the persistent follicle participate in the attachment of ova and developing embryos to the interfilamental junctions of inner and outer demibranchs, where embryos are incubated until hatching as late-stage pediveliger larvae. Ripe eggs are large (about 250 ìm diameter) being their development entirely lecitotrophic; tissue connections of developing embryos with the maternal individual only play a mechanical role, providing support and possibly facilitating the accommodation of a high number of embryos to maximize the branchial space available for brooding.