McFall-Ngai, M. and M. K. Montgomery. 1990. The anatomy and morphology of the adult bacterial light organ of Euprymna scolopes Berry. Biological Bulletin 179: 332-339.
The light organ of Euprymna scolopes allows the squid to give beautiful displays of light. The symbiont Vibrio fischeri is responsible for producing the light and is housed in a chamber inside the light organ, which in turn is enclosed within the mantle cavity next to the ink sac. With no opening to the outside, how does the squid control the expression of light?
The light organs of a young E. scolopes appear mature and follow a complex development process. The organ itself is made of tissues that were customized so that the squid can utilize the light economically while providing a favourable environment for the bacteria. And there are reflective tissues that surround the bacteria chamber.
Specimens were collected and kept in recirculating aquaria until they were needed. Then the light organs were fixed and tested for ultrastructural detail. It was noted that the positions of the reflector (reflective tissues), the ink sac, and the bacterial tissues were varied. On the ventral surface of the light organ, a thick, transparent lens is continuous with the lining of the ink sac.
The symbiotic bacteria produce light continuously, so to regulate their light display, this squid must vary the position of the reflective tissues relative to the light organ.
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