Sites of bioluminescence in the appendicularians Oikopleura dioica and O. labradoriensis (Urochordata: Larvacea)

Although bioluminescence is known in larvacean tunicates, its origin has not been reported. Two species, Oikopleura dioica and O. labradoriensis, from the northeastern Pacific Ocean, were examined during 1979–1982 to determine the sites of luminescence. An appendicularian lives within a secreted, mucous house, and its body is tightly invested by a house rudiment. Mechanical stimulation elicited multiple, summated blue-green flashes from free individuals invested by house rudiments and from empty houses that were virtually free of contamination by exogenous luminescent bacteria or dinoflagellates. Direct microscopic observations showed that the light is produced by clusters of 1 to 2 m fluorescent granules that form intricate, species-specific patterns of inclusions in the house rudiment. These granular inclusions are probably present in the expanded house, where they account for the multiple, point-sources of light observed in flashing houses. Neither fluorescence nor luminescence were observed in any other parts of the house rudiments, expanded houses, or free appendicularians (including the oral glands, which were previously suspected of producing bioluminescent secretions).