FISHERY BULLETIN: VOL. 72. NO. 2 



Our studies of the larvae of this family have 

 included material from all oceans. We have been 

 able to identify larvae from all recognized genera 

 except Hintonia and Dorsadena. Larval evidence 

 supports giving generic status to Metelectrona and 

 Parvilux. Including these, we have developmental 

 series for 29 myctophid genera and for many gen- 

 era we have series for all known species. This has 

 afforded a more comprehensive view of the range 

 and variability of larval characters, and we are 

 increasingly impressed with the functional inde- 

 pendence of the larval and adult characters. It is 

 apparent that the world of the larvae and the 

 world of the adults are two quite separate 

 evolutionary theaters. Our studies of larval 

 lanternfishes have disclosed a full range of charac- 

 ters, from generalized to specialized and from con- 

 servative to labile, equal in scope to those of the 

 adults. These characters fall into several 

 categories. An important group is the shape of 

 various structures such as the eye, head, trunk, 

 guts, and fins, especially the pectoral fins. Another 

 group is the sequence of appearance and the posi- 

 tion of fins, photophores, and bony elements. 

 Another is the size of the larvae when fins and 

 other features appear and the size of the larvae 

 when they transform into juveniles. Pigmentation 

 provides an important group of characters based 

 on the position, number, and shape of melano- 

 phores. Finally, there are the highly special- 

 ized larval characters such as voluminous fin 

 folds, elongated and modified fin rays, chin bar- 

 bels, preopercular spines, etc. It is our purpose 

 here to point out some of these characters and 

 demonstrate how they can be of advantage in 

 defining taxa and establishing phylogenetic 

 lineages. 



THE SUBFAMILY MYCTOPHINAE 



The most trenchant character of larval myc- 

 tophids is eye shape. Our studies show that 

 lanternfish larvae fall naturally into two groups 

 on the basis of eye shape — those with narrow ellip- 

 tical eyes and those with round or nearly round 

 eyes (Moser and Ahlstrom, 1970). The species 

 composition of these two groups agrees closely 

 with that of the two subfamilies, Myctophinae and 

 Lampanyctinae, established by Paxton (1972) on 

 the basis of osteological and photophore charac- 

 ters of adults. Larvae of the Myctophinae have 

 elliptical eyes; some species have ventral pro- 



longations of choroid tissue and some have the 

 eyes on stalks. Paxton recognized 11 genera in 

 the subfamily Myctophinae and distributed them 

 into two tribes, the Myctophini and the Gonich- 

 thyini. Larvae of the species in each of these 

 genera generally conform to a particular morph 

 based on form, pigment, and developmental 

 pattern and, although these morphs are remark- 

 ably diverse, we can find no character or set of 

 characters that would divide the genera into 

 tribes. Within each genus of the subfamily, how- 

 ever, the larval characters are indispensible in 

 delineating groups of related species or subgenera. 

 This is best illustrated by examining the impor- 

 tant genera of the Myctophinae. 



Protomyctophum larvae have a slender shape 

 (Figure 1). For all species exceptP. anderssoni, the 

 gut is short during most of the larval period and 

 characteristically there is a marked interspace 

 between the anus and the origin of the anal fin 

 (Figure lA-D). The gut elongates dramatically in 

 late larvae, to fill the interspace. Gut development 

 is completely dissimilar in P. anderssoni, where 

 the gut is long at all larval sizes, in fact longer 

 than in most other lanternfish larvae (Figure IE). 

 Series of ventral tail melanophores are formed in 

 some species of both recognized subgenera 

 (Heirops and Protomyctophum sensu stricto), for 

 example in P. Protomyctophum normani (Figure 

 lA) and P. Heirops thompsoni (Moser and Ahl- 

 strom, 1970). Larvae of the subgenera can be sepa- 

 rated, however, on the basis of eye shape, the eyes 

 of Heirops (Figure IC, D) being characteristically 

 narrower than those of Protomyctophum sensu 

 stricto (Figure lA, B). Choroid tissue is absent 

 from the ventral surface of the eye in all species of 

 the genus except P. anderssoni, which has a well- 

 developed "teardrop" (Figure IE). Larvae of P. 

 anderssoni are so markedly different from those of 

 all other species of Protomyctophum, which 

 otherwise form a rather cohesive group, that this 

 species should be placed in a separate subgenus or 

 perhaps even in a distinct genus. This suggestion 

 is supported by the unique placement of certain 

 photophores and by the structure of the sup- 

 racaudal luminous tissue in adults of this species. 



Larvae of the genus Electrona are a less 

 homogeneous group but are united by a common- 

 ality of body shape and especially gut shape (Fig- 

 ure 2). A marked interspace is present between 

 the end of the gut and the origin of the anal fin. 

 This space is closed only at the termination of the 



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