The pyloric caeca and posterior intestine of Howella brodiei are bioluminescent, and are associated with internal reflective tissues. The bioluminescence is not bacterial in origin. Unlike that of several shallow water apogonids, it does not depend upon Vargula luciferin. Florenciella lugubris has bioluminescent oesophageal diverticula and is able to eject a pulse of luminescent material from beneath the operculum.
The luminescence of the two species is compared with that of other perciform fishes.
The perciform family Apogonidae (cardinal fishes) contains several bioluminescent coastal species in the Indopacific genera Siphamia, Rhabdamia, Archamia, and Apogon. Their oceanic relatives are less well known and their systematic position is still a matter of some conjecture. Howella has been assigned to the Apogonidae but has also been included in the Moronidae (Tortonese, 1986), and, more recently, in the Percichthyidae (Post & Quéro, 1991). Some authors have followed Mead & De Falla (1965) in assigning the oceanic apogonid-like fishes to the family Cheilodipteridae (e.g. Fedoryako, 1976), in recognition of the fact that they ‘are so different from their coastal relatives that comparison is pointless’ (Mead & De Falla, 1965).
Bioluminescence has not been described in detail in any of the oceanic species. Mayer (1974) reported that one of the pyloric caeca in Epigonus macrops was separated from the others and associated with reflective structures. This strongly suggested that it was bioluminescent, based on comparisons with known luminescent shallow water perciforms, such as species of Pempheris and Parapriacanthus. Mead & De Falla (1965) described a ventral reflective strip in Rosenblattia robusta which, by analogy with similar appearances in luminous neritic species, they considered a possible indication of bioluminescence.