OKIYAMA: MYCTOPHIFORMES 



257 



Table 69. Similarity Matrix of 1 5 Families of Mvctophiformes. Based on the total number of characters shared in the same state regardless 



of the primitive or denved (below the diagonal) and that of the shared derived states (above the diagonal, with similarity index in parentheses). 



Subordinal groups are indicated by enclosure. Similarity index is calculated by the following formula: P„ = (C,/\/S,S,) x 100, where S, and S, 



are number of derived characters in families i and j, and C„ is number of the shared derived states between the same set of families. 



My 



Ip 



Sy 



or frontal ridges. Development of head armature generally oc- 

 curs in the forms with a massive head more than 30% of body 

 length, thus suggesting the specialized condition of this char- 

 acter. Several myctophid species {Lampanyctus) having pre- 

 opercular spines provide a fine example of this trend, while this 

 is not the case in Scopelarchidae. According to Nafpaktitis(1977), 

 the character state of Neoscopelus is assigned to the Neosco- 

 pelidae. The states recognized are: (0) = Head armature absent. 

 (1) = Head armature present. 



Body shape f/A — The general body shape can range from ex- 

 tremely slender and elongate to stubby and deep. These are 

 tentatively grouped into three character states with possible evo- 

 lutionary trends towards the opposing directions from the mod- 

 erately slender body shape shared by primitive groups such as 

 Aulopidae and Chlorophthalmidae. The character states rec- 

 ognized are: (0) = Body moderately elongate. (1) = Body ex- 

 tremely slender and elongate. (2) = Body stubby and deep. 



Pigment spots or area ("(SA— Johnson (1982) suggested the po- 

 tential importance of pigmentation other than the peritoneal 

 sections in the systematics of the Myctophiformes, even at high 

 taxonomic levels. A difficulty in this regard is how to recognize 

 the meaningful character states. Based on the various pigmen- 

 tation patterns in the tails of larvae (posterior to the anus except 

 for the caudal fin) such as (a) absent, (b) present along only the 

 ventral midline, and (c) present along lateral or dorsal surfaces 

 of body sometimes forming clear bands, formal recognition of 

 this character is undertaken. Since patterns (a) and (b) are shared 

 commonly during the ontogeny of the same species, two char- 

 acter states are recognized with the assumption that (c) repre- 

 sents the derived state. (0) = Pigment spots or areas in tail absent 

 or present along only the ventral midline. (1) = Pigment spots 

 or areas in tail present along lateral or dorsal surface. 



The primitive or derived states for these eight characters are 

 summarized in Table 68. Family level designation of character 



states is mostly based on the assumption of Johnson (1982) that 

 "possession by one or more representatives of a particular OTU 

 of a state considered primitive indicates (except where contrary 

 evidence can be cited) the primitiveness of that state for that 

 OTU." 



A similarity matrix based on the total numbers of characters 

 shared in the same state, regardless of whether the states are 

 primitive or derived, is given below the diagonal in Table 69. 

 Above the diagonal are shown the numbers of derived characters 

 shared in the same state and the similarity index calculated on 

 the same data. These two sets of figures are expected to reveal 

 certain clues to clarify the interfamilial associations of this order 

 from the larval standpoint. 



AiiLOPOiDEi: Aulopidae 



So far as the selected larval characters are concerned, the 

 Aulopidae can not be separated from the Chlorophthalmidae. 

 This unclear distinction is due to the limited numbers of char- 

 acters selected, because other larval and adult features shown 

 in Table 70 reveal the trenchant differences between them. Of 

 these, the possession of maxillary teeth and fulcral scales, and 

 the earlier differentiation of the peritoneal pigment spots well 

 justify the distinct and less specialized systematic status of the 

 Aulopidae. Other aspects of sharp contrast such as in the den- 

 tition, particularly of the basihyal, and gut morphology sub- 

 stantiate the above conclusion. 



Although the diversity within the Aulopidae once suggested 

 on the basis of larval characters (Okiyama, 1974b) has proved 

 to be unacceptable, there still remain problems concerning the 

 monotypic nature of this family. As mentioned elsewhere (Oki- 

 yama, 1979b), it is likely that the Myctophiformes evolved along 

 several lines, one of the major trends being the elongation of 

 the body shape accompanying an increase in vertebral number. 

 Obviously, aulopids lie near the base of this trend with clear 

 orientation toward an increase in the number of abdominal 

 components. The uniquely elongated larval oesophagus in A. 



