BACTERIAL SYMBIONTS COLONIZE THE ACCESSORY NIDAMENTAL GLAND OF THE SQUID LOLIGO-OPALESCENS VIA HORIZONTAL TRANSMISSION

The accessory nidamental gland (AN gland), a reproductive organ of the mature female squid Loligo opalescens, harbors a dense culture of bac teria of unknown function. A multilayered sheath surrounding the L, op alescens egg case is similarly colonized by bacteria that presumably o riginate in the AN,oland, as evidenced by their presence in the egg ca se at oviposition. This study investigates how these bacteria are tran smitted to juvenile squid and examines some morphological consequences of bacterial colonization of AN gland tissues. By observing the struc ture of the AN gland in adults and the development and bacterial colon ization of the gland in juveniles raised in captivity, we determined t hat the AN gland was absent in newly hatched squid and did not appear until 87 days post-hatching. At 129 days posthatching, the organ displ ayed tubules composed of a single layer of epithelial cells and expres sing numerous cilia and microvilli. These tubules were not yet fully f ormed and thus were open to the mantle cavity and external seawater, p ossibly to aid in the acquisition of microorganisms. Since the AN glan d developed a considerable time after hatching, it most likely acquire s its symbionts horizontally from environmental seawater and not verti cally from the egg case sheath. The switch from expression of cilia to production of microvilli on the epithelial cell surface may dictate t he competence of the tissue for bacterial colonization, Electron micro scopic examination of juvenile and adult AN glands revealed that an an alogous process occurs during the development of the related light org an of other cephalopod species that harbor symbiotic bacteria.