ROLE OF LARVAL STAGES IN SYSTEMATIC INVESTIGATIONS 

 OF MARINE TELEOSTS: THE MYCTOPHIDAE, A CASE STUDY^ 



H. Geoffrey Moser and Elbert H. Ahlstrom^ 



ABSTRACT 



The lanternfish family Myctophidae is the most speciose and widespread family of mid- water fishes in 

 the world ocean. As presently recognized it contains about 30 genera and 300 nominal species. Their 

 larvae are highly prominent in the plankton and make up about 50% of all larvae taken in open-ocean 

 plankton tows. 



Our studies of myctophid larvae, on a worldwide basis, have demonstrated that characters of the 

 larval stages of lanternfishes are of great utility in systematic analysis. The genera and species can be 

 recognized on the basis of eye and body shape, the shape and length of the gut, and pigment pattern and 

 by the sequence of photophore development. In this paper the larvae of 55 species representing 24 

 genera are illustrated and used to demonstrate the usefulness of larvae in understanding the relation- 

 ships of species within genera. 



Characters of the larvae provide insight into generic affinities of lanternfish, allowing us to construct 

 an evolutionary scheme of tribes and subfamilies that differs in some aspects from those proposed on 

 the basis of adult characters. The concept of using larval characters in combination with adult 

 characters to delineate phylogenetic lines in myctophids is discussed, as is our view of evolutionary 

 strategy in the family. 



A major facet of comprehensive systematic inves- 

 tigations is the search for functionally unrelated 

 characters. Whether the independence of these 

 characters is actual or merely apparent, they con- 

 stitute useful elements in the analysis of systema- 

 tic relationships. Ample evidence of this is the 

 higher classification of teleosts (Greenwood et al., 

 1966) generated by the synthesis of a diverse 

 array of classical taxonomic characters. The re- 

 cent surge of serological and biochemical studies 

 on fish has placed a fresh group of characters in the 

 hands of systematic ichthyologists (De Ligny, 

 1969). Likewise, recent advances in fish cytogene- 

 tics (e.g., Ohno, 1970; Benirschke and Hsu, 1971; 

 Ebeiing, Atkin, and Setzer, 1971) are providing 

 another group of taxonomic characters. It is likely 

 that behavioral science will be still another source 

 of taxonomic characters, as exemplified by the 

 growing body of information on the acoustic be- 

 havior of fishes (Fish and Mowbray, 1970). 



One group of well known taxonomic characters, 

 those of the embryonic and larval stages, has re- 

 ceived scant attention from all but a few systema- 

 tic ichthyologists. Characters of the larvae have 



'This paper was presented at the International Symposium on 

 the Early Life History of Fish (sponsored by lABO, FAO, ICES, 

 ICNAF, and SCOR) held at Oban, Scotland, 17-23 May 1973. 



^Southwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, La Jolla, CA 92037. 



Manuscript accepted Agust 1973. 



FISHERY BULLETIN: VOL. 72, NO. 2, 1974. 



played a large role in the taxonomy of anguil- 

 liform fishes (Castle, 1969) partly because of the 

 conspicuousness of eel leptocephali and partly be- 

 cause of the unavailability of adults of many of the 

 families. Bertelsen's (1951) treatment of the 

 ceratioid fishes is a superb example of the value of 

 utilizing larval stages in a systematic revision of a 

 large group of teleosts. Apart from these two 

 groups, it is the larvae of myctophiform fishes 

 which have received the most attention from tax- 

 onomists. Ege (1953, 1957) relied heavily on lar- 

 val stages in his extensive works on the 

 Paralepididae. Johnson (1971) employed larval 

 characters in defining species and genera of 

 Scopelarchidae. Bertelsen, Marshall, and Krefft 

 (pers. commun.) have used larval stages exten- 

 sively in their revision of the Scopelosauridae. 

 Our studies on the family Myctophidae itself 

 (Moser and Ahlstrom, 1970, 1972) indicated that 

 larval characters can aid significantly in differen- 

 tiating taxa and defining evolutionary lineages 

 within this family. 



The lanternfish family Myctophidae is the most 

 speciose and widespread family of mid-water 

 fishes in the world ocean. As presently recognized 

 it contains about 30 genera and 300 nominal 

 species. Their larvae are highly prominent in the 

 plankton and make up about 50% of all larvae 

 taken in open-ocean plankton tows. 



391 



