MOSER and AHLSTROM: DEVELOPMENT OF SCOPELOPSIS MULTIPUNCTATUS 



though the following larger and more distinct 

 primary photophores stand out on the 17.5-mm 

 specimen: POi^, PVOi and 2, VLO, VO, SAO1.3, 

 POLi-3, Pre. 



In the 17.4-mm juvenile it is evident that the 

 photophores on the body are on the posterior 

 margin of each scale pocket, thus explaining 

 their regular arrangement into horizontal rows. 

 The specimen is partially skinned, but one can 

 see that some body photophores remain decidedly 

 larger than others (notably two of the PO, the 

 VLO, and VO), while generally the distinction 

 between primary and secondary organs is less 

 marked. On the head, certain of the cheek photo- 

 phores remain large and distinct and, additional- 

 ly, the two-part Dn is now present as are the 

 small anterior and posterior Br. 



Opinion has been divided on whether or not 

 the dichotomy of primary and secondary photo- 

 phores, described above, is present in adult 

 Scopelopsis. In his original description Brauer 

 (1906) did not distinguish between primary and 

 secondary organs. Taning (1932) stated that 

 some of the organs were larger than others and, 

 moreover, made the important observation that 

 the scales over these larger organs were equipped 

 with a special lenslike modification typical of 

 other myctophids. He noted that among the 

 prominent photophores were a PLO, two PVO, 

 a VLO, three SAO in a rather steep line, and two 

 POL in a horizontal line. His statement, "... in 

 fact we find all the diff'erent groups of organs 

 which we have in all other species of the sub- 

 family Myctophini, small, but larger than the 

 very small organs scattered all over the body . . ." 

 was unaccompanied by an illustration. Fraser- 

 Brunner (1949) recognized that certain photo- 

 phores were more highly developed than others 

 and termed these primary organs in contrast to 

 the less highly developed secondary organs. He 

 gave the following formula: "PLO above, both 

 PVO below base of pectoral. Five PO. Five VO. 

 Three SAO in an oblique series. AO in two ser- 

 ies. Two POL in horizontal series. Five or more 

 Pre." His accompanying illustration shows the 

 basic photophore pattern but is somewhat il- 

 legible, especially in the caudal region. Naf- 

 paktitis and Nafpaktitis (1969) could not dif- 

 ferentiate primary and secondary photophores 



in their material. Wisner (in press) employed 

 a large series of excellently preserved specimens 

 in his description of Scopelopsis and showed that 

 the ability to diflTerentiate primary from secon- 

 dary photophores is dependent on the condition 

 of the specimen. In specimens which had re- 

 tained most of their scales he identified primary 

 photophores as those with a lenslike modification 

 of the overlying scale. His photophore formula 

 and clear illustration corroborate the observa- 

 tions of Taning (1932) and Fraser-Brunner 

 (1949); further refinements include his obser- 

 vation of 7-10 anterior AO, 5-6 posterior AO, 

 4-6 Pre, 2 or 3 POL, and 3 prominent cheek 

 photophores in a diagonal line anterior to the 

 preopercle. Additionally he shows definitively 

 the two-part Dn and the embedded Vn. The ob- 

 servations of Taning (1932), Fraser-Brunner 

 (1949), and Wisner (in press) along with the 

 evidence presented herein demonstrate that cer- 

 tain of the multitudinous light organs of Scopel- 

 opsis are more highly developed than others and 

 that these "primary organs" are arranged in a 

 pattern that corresponds to the general pattern 

 of other members of the family. Our observa- 

 tions on ontogenetic series largely confirm the 

 arrangement of primary photophores postulated 

 by these authors, but some of our findings sug- 

 gest discrepancies that may only be clarified by 

 further examination of undamaged adults. For 

 example, we find only four well-developed PO 

 and a single large VO in transforming specimens 

 and in juveniles and adults available to us. This 

 as well as the exact frequencies of AO and Pre 

 series await elucidation by workers with large 

 series of intact adults. 



SYSTEMATIC RELATIONSHIPS 



The efficacy of using the larval and transfor- 

 mation stages of lanternfishes to elucidate spe- 

 cific and supraspecific relationships has been 

 clearly demonstrated (Pertseva-Ostroumova, 

 1964; Moser and Ahlstrom, 1970). We (Moser 

 and Ahlstrom, 1970) showed that the genera of 

 Myctophidae can be divided into two groups on 

 the basis of larval eye shape — those with narrow 

 elliptical eyes and those with round or nearly 



549 



