MOSER and AHl.STROM: ROLE OF LARVAE IN SYSTEMATICS 



specimen. Only larvae of M. lychnobium have 

 been taken in the eastern Pacific, whereas both 

 species have been taken in the central and west- 

 ern Pacific and in the Indian Ocean. Taxonomists 

 dealing with adult characters only, have placed M. 

 lychnobium in synonymy with M. spinosum but 

 the distinctiveness of the larvae suggests that the 

 adult characters should be reexamined. 



The larvae ofM. spinosum andM. lychnobium, 

 although clearly developing the Dn pair of photo- 

 phores, resemble the larvae of M. punctatum in 

 body shape and pigmentation, a species which 

 does not develop the Dn as larvae. Actually, there 

 are some common characters of pigmentation and 

 eye structure which appear in all of the groups of 

 Myctophum species described above. What we ap- 

 pear to be dealing with is a mosaic of larval 

 characters in a highly complex genus. The tax- 

 onomy of Myctophum presently is confused; our 

 work on the larvae should help define the number 

 of species in the genus and, perhaps, adult charac- 

 ters will emerge that can be combined with larval 

 characters to define the phyletic lines within the 

 genus. 



Larvae of the four genera known collectively as 

 the slendertailed myctophids are shown in Figure 

 8. Quite obviously there are two highly divergent 

 generic pairs. Loweina and Tarletonbeania are 

 characterized by large oval eyes, posterior place- 

 ment of median fins to accommodate the immense 

 fin fold, and elongated lower pectoral rays bearing 

 spatulate processes. Gonichthys and Centrobran- 

 chus are characterized by a deep but markedly 

 compressed head and body and small narrow eyes 

 with extremely elongate choroid tissue. As stated 

 earlier, the larval characters suggest strongly 

 that the two generic pairs are not closely related 

 and should not be grouped into a tribe. The 

 Gonichthys-Centrobranchus pair is similar in eye 

 shape and gut shape to some species of Myc- 

 tophum, however no species o{ Myctophum even 

 approaches this pair in body shape. The characters 

 of the other pair are so divergent as to give no 

 clue of their affinities within the subfamily 

 Myctophinae. 



THE SUBFAMILY 

 LAMPANYCTINAE 



The subfamily Lampanyctinae is considerably 

 larger than the Myctophinae; it contains about 19 

 genera and 200-250 species compared with 12 



genera and about 75 species in the Myctophinae. 

 Paxton (1972) divided the genera into four tribes 

 on the basis of a combination of osteological fea- 

 tures and characters of the photophores. In a pre- 

 vious paper (Moser and Ahlstrom, 1972) we dis- 

 cussed Paxton's placement of genera in these 

 tribes and indicated that the larval characters 

 suggested a somewhat different distribution of 

 genera among the four tribes. For the purposes of 

 this discussion the tribes referred to here are those 

 suggested by the larval characters. 



In general, the larvae of the Lampanyctinae are 

 much less diverse in larval characters and 

 specializations than are the larvae of the Myc- 

 tophinae, although exceptions to this may be 

 found in two of the lampanyctine tribes, the 

 Diaphini and the Lampanyctini. 



The tribe Diaphini is made up of two genera 

 — Diaphus contains about 50 species and Lobian- 

 chia has 3 species. Both genera develop photo- 

 phores, in addition to the Br2, during the larval 

 period; in fact more are developed in Diaphus 

 than in any other lanternfish genus. 



There are two basic larval types in Diaphus 

 (Figure 9A, B). One has a slender body, small 

 head, and a series of persistent melanophores on 

 the ventral midline of the tail. The other type has 

 a deeper body, bulbous head, and a single persis- 

 tent ventral tail melanophore, or none. It is excep- 

 tional for larvae of either type to develop pigment 

 on the head and it never occurs between the eyes, 

 as is common in Lampanyctus. Both types do form 

 embedded melanophores at the base of the caudal 

 fin rays. 



The slender type is restricted to the species that 

 develop a suborbital photophore as adults 

 [Diaphus sensu stricto of Fraser-Brunner, 1949) 

 and is represented in Figure 9A by D. theta. The 

 stubby type is represented by D. pacificus (Figure 

 9B). The specimens illustrated for the two species 

 are rather early larval stages which have not yet 

 formed their larval photophores, other than the 

 Br2. The first additional pair to form in both types 

 is the PO5 and then the POi (Table 3). The large 

 genus Diaphus, except for the Atlantic species 

 ably reviewed by Nafpaktitis (1968), is in a state of 

 taxonomic confusion. Various workers (Fraser- 

 Brunner, 1949; Bolin, 1959) have attempted to 

 split the genus into smaller, more cohesive groups; 

 the larval evidence would suggest that at least two 

 divergent groups are present. 



The larvae of the three species ofLobianchia are 



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