MOSER and AH I STROM: ROLE OF LARVAE IN S't STEMATICS 



but these coalesce into one or two spots in mid- 

 stage larvae. Triphoturus larvae are character- 

 ized further by their distinctive head shape and by 

 the series of melanophores along the ventral mid- 

 line below the gut. Stenobrachius larvae add con- 

 siderable pigment late in the larval period, par- 

 ticularly along the dorsum and on the myosepta 

 of the trunk. The larvae of Parvilux are distinct 

 in shape and pigmentation. Paxton (1972) placed 

 this genus in Lampanyctus based on osteological 

 characters. In certain photophore arrangements, 

 however, particularly in the posterior placement 

 of the VLO and the nonangulate arrangement of 

 the SAO, the genus appears to us to be more 

 closely related to Stenobrachius than to Lam- 

 panyctus. These characters in addition to the dis- 

 tinctness of the larvae would suggest that the va- 

 lidity of Parvilux should be reconsidered. 



The tribe Gymnoscopelini judged from larval 

 and/or adult characters contains a dozen genera 

 {Notoscopelus, Lampichthys, Scopelopsis, Cerato- 

 scopelus. Lepidophanes. Bolinichthys, Lampadena, 

 Taaningichthys, Dorsadena, Lampanyctodes, 

 Gymnoscopelus, and Hintonia). The larvae 

 of these genera are united by a group of common 

 characters, including a distinctive, usually 

 slender, body outline, a series of melanophores 

 on the dorsal and ventral midlines of the tail 

 (in most genera), and the development of a 

 group of photophores during the larval period, 

 most notably the PO5, FLO, and Vn. The larvae of 

 this tribe were treated extensively in a previous 

 paper with representative larvae illustrated for 10 

 of the 12 genera (Moser and Ahlstrom, 1972). Ad- 

 ditional species of Bolinichthys (B. supralateralis, 

 Figure IID), Ceratoscopelus (C. townsendi, Figure 

 HE), Lampadena (L. luminosa. Figure 12B), 

 Lepidophanes (L. gaussi. Figure 12C) are illus- 

 trated herein. Illustrations of Notoscopelus re- 

 splendens (Figure 12 A) and Scopelopsis mul- 

 tipunctatus (Figure 12D) are included for com- 

 parative purposes. It need only be mentioned here 

 that the clusters of closely related genera within 

 this tribe are readily apparent from examining 

 the larval characters, especially the sequence of 

 photophore development, and these groupings 

 agree closely with those established on the basis of 

 adult characters. 



The species Notolychnus valdiviae has so many 

 unique adult characters that Paxton (1972) as- 

 signed it to the monotypic tribe Notolychnini. 

 Likewise the larva has a number of unusual 

 characters (Figure 12E). The shape of the eye is 



variable from specimen to specimen; it can be nar- 

 row and elliptical or nearly round, but most typi- 

 cally would be classified as irregular in shape. The 

 shape of the head, body, and gut is unusual and 

 distinctive. The larval characters are of little help 

 in elucidating the affinities of this species within 

 the Myctophidae and, when added to the list of 

 unique adult characters, only magnify the prob- 

 lem. It would seem to make just as much sense to 

 establish a separate subfamily for Notolychnus as 

 to place it in a monotypic tribe in the subfamily 

 Lampanyctinae. 



The larvae illustrated in this paper comprise 55 

 species representing 24 genera. Illustrations are 

 included for larvae of 11 of the 12 genera in the 

 subfamily Myctophinae; not included are illustra- 

 tions of Diogenichthys (see Moser and Ahlstrom, 

 1970 for D. laternatus and D. atlanticus). In the 

 subfamily Lampanyctinae larvae are illustrated 

 for 13 of the 19 genera. The omitted genera {Lam- 

 pichthys, Lampanyctodes, Gymnoscopelus, and 

 Tanningichthys), all from the tribe Gymnoscope- 

 lini, are illustrated in Moser and Ahlstrom (1972). 

 Larvae of Hintonia and Dorsadena have not yet 

 been identified. 



SOME EVOLUTIONARY 

 CONSIDERATIONS 



With this brief review of lanternfish larvae 

 completed, let us now turn to an interesting prob- 

 lem of myctophid evolution to which study of the 

 larvae may contribute importantly — the evolu- 

 tion of photophore pattern. With a single excep- 

 tion, all adult myctophids have two conspicuous 

 rows of photophores that extend the length of the 

 body on each side of the ventral midline. The 

 photophores are grouped and positioned in a 

 definite and often diagnostic pattern. Also, 

 lanternfishes have a specific pattern of photo- 

 phores on the sides of the body, below the lateral 

 line, and on the ventral aspect of the head. The 

 exception is Taaningichthys paurolychnus, which 

 appears to lack body photophores entirely. In ad- 

 dition to these photophores, some lanternfish gen- 

 era have photophores positioned in a pattern 

 above the lateral line and some have small "sec- 

 ondary" photophores distributed more generally 

 over regions of the body and head. Another type of 

 luminous structure present on most myctophids 

 are discrete glands located at the caudal peduncle. 

 Typically, these are sexually dimorphic in charac- 

 ter and, doubtless, play some part in courtship 



409 



