DAVY: REVIEW OF LANTERNFISH GENUS Taaningichthys 



primary photophores, retaining only the caudal 

 glands and the simple, presumably secondary, 

 photophores, on the head and caudal fin. It is 

 also the deepest dwelling of the three species. 



Gravid females have been captured in March- 

 April and August-September. The smallest 

 gravid female examined was 65 mm. 



Horizontal distribution — T. pam'ohjchnus is 

 distributed circumglobally between about lat 40° 

 N and 20° S (Figure 5). It does not appear to 

 be as common as T. bathyphilus. 



Vertical distribution — T. paurolychnus has 

 not been taken above 900 m (an adult female, 

 77 mm). The lower limits of its distribution 

 are not yet known. T. paurolychnus does not 

 appear to perform daily vertical migrations. 



Etymology — The name paurolychnus refers 

 to the absence of primary photophores and the 

 presence of limited, presumably secondary pho- 

 tophores. It is derived from the Greek pauros 

 meaning few, small, and lychnus meaning light. 



OTOLITHS 



OL as a percentage of SL ranges from 4.4 to 

 5.5% in T. minimus, 3.9 to 4.6% in T. bathy- 

 philus, and 2.8 to 3.6% in T. paurolychnus. OH 

 as a percentage of OL ranges from 66.7 to 77.7% 

 in T. minimus, 72.1 to 77.9% in T. bathyphilus, 

 and 78.3 to 91.7% in T. paurolychnus. 



The sulcus is more pronounced in the otolith 

 of T. bathyphilus than it is that of T. paurolych- 

 nus, but less so than in that of T. minimus (Fig- 

 ure 6). The otolith of T. paurolychnus has al- 

 most no antirostrum, and the antirostrum in T. 

 bathyphilus is less pronounced than that in T. 

 minimus. The posterior margin of the otolith 

 in T. paurolychnus is nearly straight vertically, 

 making the general outline almost square, where- 

 as the otoliths of its two congeners are smoothly 

 rounded posteroventrally, so that the general 

 outline is oval. The otolith (Figure 6) of a 

 single specimen of T. bathyphilus from the north 

 Atlantic is differently shaped and very large 

 for a specimen of its size (60 mm). However, 

 no other differences in the fish were found and 

 more material from the north Atlantic must be 

 examined before anything further can be stated. 



DISCUSSION 



The various hypotheses and ideas regarding 

 the function, or functions, of luminous organs 

 of midwater fish are reviewed by Nicol (1969). 

 The photophores within the genus Taaningich- 

 thys show drastic reduction in terms of numbers 

 and development. T. minimus has, relatively, 

 the best developed photophores as well as the 

 greatest number; these organs are seldom 

 rubbed ofl[" unless the specimen is damaged. T. 

 bathyphilus has fewer and less well-developed 

 photophores which are easily rubbed ofl". T. 

 paurolychnus has lost all primary photophores 

 but retains simple, presumably secondary, photo- 

 phores on the snout and caudal fin. As already 

 mentioned, there are no indications that the 

 members of the genus Taaningichthys undertake 

 diel vertical migrations as most myctophids do. 

 It may therefore be that i:)hotophores of the myc- 

 tophid type are not selected for in a deep-water, 

 nonmigratory fish, which would account for the 

 reduction of these organs and, eventually, their 

 loss. Unlike photophores, eyes are very well de- 

 veloped in Taaningichthys, regardless of depth of 

 occurrence. Even the deepest of the species has 

 large, nearly binocular eyes. This may be corre- 

 lated with the food habits of these fish. Mycto- 

 phids, in general, feed on zooplankters, many, if 

 not most, of which are bioluminescent. It is pos- 

 sible therefore that Taaningichthys strongly de- 

 pends on large, presumably highly eflFective eyes 

 for locating and capturing its prey, which is 

 probably not very abundant in those dark mid- 

 water depths. Furthermore, retention of this 

 energetically expensive visual equipment may 

 account for the very poorly developed lateral 

 line system. 



ACKNOWLEDGMENTS 



I thank Basil G. Nafpaktitis of the University 

 of Southern California, Robert J. Lavenberg of 

 the Los Angeles County Museum of Natural 

 History, and Theodore W. Pietsch of the Uni- 

 versity of Southern California for their critical 

 review of the manuscript and helpful sugges- 

 tions. Thanks are also due to John E. Fitch 



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