Scomberesox 



V 



A 



Nanichthys 



Cololobis (d go) 



Elassichthys 



Scomberesox 



B 



Cololobis 



Elossichfhys Xb) 



Nanichthys 



Figure 3.— Diagrams (A and B) of hypothetical divergent 

 evolution within the Scomberesocidae: b — well-developed beak; 

 d— dwarfism; g— gas bladder lost; o— ovary smgle. (A) The 

 larger Scom6eresax and the dwarfed Nanic/if/iys, and the larger 

 Cololabis and the dwarfed Elassichthys, derived respectively 

 from beaked and beakless ancestors; development of a beak 

 occurred but once, dwarfism and structural changes id g ol twice. 

 (B) The beaked and beakless larger forms. Scomberesox and 

 Cololabis. derived from a common ancestor, as did the beaked 

 and beakless dwarfs. £iissicAr/i_vs and A'an^cAMvs ; development 

 of a beak occurred twice, dwarfism and the structural changes 

 but once. 



once, SO that Elassichthys and Nanichthys are of 

 immediate common origin. On this hypothesis, the 

 beak would have developed independently in 

 Nanichthys and Scomberesox . The differences be- 

 tween the two genera in the lengths of the upper 

 and lower beaks could be cited as confirmatory 

 evidence. As another item of evidence it could be 

 stated that agreement between Elassichthys and 

 Cololabis breaks down when the structure of the 

 egg is considered. 



For some years we have known that there is a 

 distinct dwarf genus i Nanichthys) having many 



FISHERY BULl.ETIiN VOI. 77, NO :i 



characters in common with Scomberesox. as well 

 as another dwarf genus {Elassichthys) having 

 much in common with Cololabis. The species in- 

 volved we name Nanichthys simulans, new spe- 

 cies, and Elassichthys adocetus (Bohlke 1951). 



These conclusions have been rather widely 

 shared with colleagues. Parin (1968a, b) in par- 

 ticular, has discussed these putative relation- 

 ships, using the names "Scomberesox sp." and 

 "Cololabis adocetus" for the respective dwarfs; he 

 cited only superficial distinctions, along with re- 

 duced numbers of gill rakers and vertebrae, in the 

 dwarf form. Dudnik (1975bl, likewise using the 

 name "Scomberesox sp.." also discussed Nanich- 

 thys; he noted one internal morphological feature, 

 that one of the ovaries is rudimentary. We have 

 consistently found, however, no trace of a second 

 ovary in either Elassichthys or Nanichthys. Our 

 findings have been mentioned al.so by Collette 

 ( 1966) as the second case of paedomorphism in the 

 order, during his indication of a third case, that of 

 a "paedomorphic or neotenic" belonid. The first 

 case he indicated as the suggestion by Nichols and 

 Breder ( 1928) that the scomberesocid genus Col- 

 olabis is a permanently arrested stage in the on- 

 togenetic development of Scomberesox. 



526 



