the creation of a distinct genus for M. aurolater- 

 natum and it is highly probable that corroborative 

 characters will appear after careful reexamina- 

 tion of the adults. 



With the removal of M. aurolaternatum , the re- 

 maining larvae o^Myctophum form a diverse, yet 

 recognizable, group. All have large broad pectoral 

 fins supported on a highly characteristic fan- 

 shaped base. The species may be divided into two 

 groups, those which form only the Br2 photophores 

 and those which develop additional photophores 

 during the larval period. In the first group the 

 elongate larva of M. punctatum (Figure 5C) has 

 stalked eyes and a slightly aliform pectoral fin 

 base, reminiscent of Symbolophorus larvae, and 

 may be the closest relative of that genus among 

 the species of Myctophum. A closely related 

 species, M. nitidulum, is also stalk-eyed, but is 

 deeper-bodied, more heavily pigmented, and has a 

 more fan-shaped pectoral fin base (Figure 5D). It is 

 obvious from our studies thatM. nitidulum is one 

 member of a complex, that includes M. affine (not 

 illustrated) and several other species. The lightly 

 pigmented larva of M. phengodes has only a sug- 

 gestion of stalked eyes but is similar in body shape 

 toM. nitidulum (Figure 5E). The larval characters 

 substantiate Paxton's (1972) decision to abolish 

 the genus Ctenoscopelus, established for this 

 species by Fraser-Brunner (1949). 



The other major group of Myctophum is charac- 

 terized by the appearance of the Dn photophore 

 anterior to the eye, usually early in the larval 

 period. These species fall into three rather distinct 

 species groups on the basis of body and eye shape. 

 The first is a group of four rotund broad-headed 

 species, which have large unstalked eyes sub- 

 tended by a short mass of choroid tissue. Of these, 

 the larvae of M. asperum are the most heavily 

 pigmented, particularly on the body (Figure 6A). 

 Pigment is confined to the head in M. obtusirostre, 

 is heavy under the posterior part of the gut in 



FISHERY BULLETIN; VOL. 72. NO. 2 



Myctophum sp. (possibly brachygnathum) and is 

 developed on the jaws, branchistegal membrane 

 and lower part of the pectoral fin base in Myc- 

 tophum sp. (possibly /issKnoui) as seen in Figure 

 6B-D. The latter three species form the PLO 

 photophores on the pectoral fin base soon after the 

 appearance of the Dn organs (Table 2). 



Nafpaktitis (1973) has listed a number of 

 characters for distinguishing adult M. ob- 

 tusirostre from M. brachygnathum. He showed 

 that M. pristilepis is a synonym of M. brachyg- 

 nathum. The status of M. imperceptum Bekker 

 and Borodulina has yet to be determined. 



A second larval type is represented by M. 

 selenops (Figure 7A) and a closely related species 

 restricted to the Indian Ocean and Persian Gulf 

 for which we can find no adult (Figure 7B). In 

 these rotund species, the head is relatively longer 

 and narrower than in the previous group and the 

 slightly stalked eyes are narrower and bear more 

 elongate choroid tissue. The two species differ in 

 that the eyes of the unnamed larva are more 

 definitely stalked than in M. selenops. Also the 

 pigment pattern is markedly different, as is the 

 size at which photophores appear. We have care- 

 fully examined larvae of M. selenops from the At- 

 lantic, Indian, and Pacific Oceans, find them to be 

 identical in all three oceans, and seriously ques- 

 tion Wisner's (1971) allocation of the Hawaiian 

 population as a distinct species, based on slight 

 differences in relative eye size and SAO photo- 

 phore orientation. 



The third type of larvae that develop the Dn 

 photophores is represented by M. spinosum 

 (Figure 7C) andM. lychnobium (Figure 7D). These 

 are elongate fusiform larvae with moderately nar- 

 row unstalked eyes, underlain by a pronounced 

 choroid mass. M. spinosum is the more slender of 

 the two and is extremely heavily pigmented, espe- 

 cially in older larvae. Pigmentation in M. lych- 

 nobium is confined to that in the illustrated 



Table 2. — Sequence of photophore formation in species oCMyctophum that form two or more pairs 



during the larval stage. 



400 



