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ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Table 64. Character States in the Genera of Myctophidae. The 59 characters are described in Table 1.0 = plesiomorphic state, 1 = 



to represent the most primitive myctophid based on photophore 

 pattern. However Myers (1958) has shown that short jaws have 

 arisen from the long-jawed condition a number of times in 

 teleost ^ olution, and discussed their adaptive advantages. We 

 consider short jaws to be the apomorphic condition within both 

 the Myctophidae and Neoscopelidae, and moderate jaws also 

 to be derived from long jaws. (2) Extrascapulars are single in 

 neoscopelids; therefore two extrascapulars in some myctophids 

 should be the derived condition. However Paxton (1972:58) 

 described how the neoscopelid extrascapular differs in position 

 and shape from that of myctophids. Following Williston's Rule 

 we consider a single extrascapular to be derived from the fusion 

 of two elements, independently attained in each family. In Low- 

 eina the single condition has arisen through the loss of the dorsal 

 extrascapular. (4) With no outgroup with similar photophores 

 for comparison, we are unable to determine whether 1-2 or 3- 

 9 Prcs is the apomorphic state. However the two character states 

 follow subfamilial limits, and one of the states must be derived 

 and definitive for its subfamily. (6) All myctophids have at least 

 one of the orbital light organs, Dn and Vn, and most have both. 

 We are not sure whether the presence or the absence of a Dn is 

 apomorphic, but one of those stales defines a major line within 

 the Lampanyctinae. (9) Although the Neoscopelidae have a su- 

 pramaxillary, Paxton (1972:62) considered the supramaxillary 

 of some Myctophidae to be an independently derived feature. 



due to a difference in shape and its required loss at least four 

 times within the family if considered primitive. However, John- 

 son (1974b:205, 1982:79) has shown the presence of supra- 

 maxilla(e) to be primitive in other myctophiforms (sensu lato); 

 the absence of a supramaxilla in myctophids is here considered 

 a derived state through loss. (15) Although caudal luminous 

 organs are not present in neoscopelids, they are present in all 

 but three myctophid genera, where their loss is here considered 

 derived. No other characters indicate that any of the three genera 

 (Diaphus, Gymnoscopelus, Hintoma) are the most primitive in 

 the family. (17) Two or three horizontal Pols are in a linear 

 position and should be considered the plesiomorphic condition. 

 However in those genera with horizontal Pols (Notoscopelus, 

 Lampichlhys and Scopelopsis) the photophores are high, close 

 to the lateral line. We consider the primitive myctophid state 

 to be one with low photophores with none or one Pol (character 

 34). We therefore consider the horizontal position of Pols to 

 be derived, while noting the state in Hintonia is intermediate 

 between angled and horizontal. (19) Although Johnson (1982: 

 76) considered a higher number of vertebrae (42-62) plesio- 

 morphic for iniomous fishes, lower numbers of vertebrae in 

 neoscopelids and almost all myctophids indicate the higher 

 number in Gymnoscopelus is a secondary specialization in these 

 families. (23) The larval gut of some neoscopelids is long and 

 coiled, clearly a specialization foreshadowing the condition of 



