FISHERY BULLETIN: VOL. 79, NO. 1 



natural group comprised of related genera, in con- 

 trast with Norman's (1934) speculation, will de- 

 pend on a detailed analysis of derived character 

 states which is beyond the scope of this paper. 

 However, based on other larval studies mentioned 

 above, it seems probable that the larval 

 similarities wdthin the group may provide evi- 

 dence to support the idea of intergeneric relation- 

 ship. In an earlier study of larvae of M. kitt, 

 G. stelleri, and G. cynoglossus, Pertseva- 

 Ostroumova (1961) preliminarily concluded that 

 larval evidence indicated a close relationship be- 

 tween Microstomus and Glyptocephalus . 



Characters shared by larvae of members of this 

 four-genus complex and not found in other mem- 

 bers of the Pleuronectini include pigment pattern 

 (preflexion larvae) consisting of three or four post- 

 anal pigment bands which may be continuous 

 (from dorsal to ventral body margin) or discon- 

 tinuous (concentrated only near the dorsal and 

 ventral body margins); elongate, slender form of 

 preflexion larvae; angular jaw with strongly 

 oblique appearance; and tendency toward a 

 leptocephaluslike shape with development. 

 Among genera, similarities are greatest between 

 Glyptocephalus and Tanakius which share the 

 characters of continuous postanal pigment bands 

 that, later in development, become concentrated 

 mediolaterally; pigment addition as ventral 

 patches between bands; preopercular spines; and 

 pronounced leptocephaluslike shape. Embas- 

 sichthys most closely resembles Glyptocephalus 

 and Tanakius, having continuous postanal pig- 

 ment bands initially which later become discon- 

 tinuous, persisting only at the body margins; 

 pigment addition as dorsal and ventral patches 

 between bands; no head spination; a moderate 

 leptocephaluslike shape. Microstomus is most 

 distinct with postanal pigment bands discontin- 

 uous and not prominent; occipital spines in two of 

 three species; much less tendency toward long 

 leptocephaluslike shape with dorsoventral deep- 

 ening of body instead. If strong pigment banding 

 and pronounced leptocephaluslike shape can be 

 shown to be derived character states, which they 

 appear to be considering the rest of the Pleuronec- 

 tini, this group of genera may indeed be related, 

 with Microstomus being least specialized and 

 Glyptocephalus most specialized. 



Additional observations on head spine patterns, 

 extremes in larval form, and eye position in rela- 

 tion to caudal fin development may prove to be 

 useful in future studies assessing relationships 



within this group of genera. Evseenko (1979) 

 theorized that the presence of head spines in 

 flatfish larvae was indicative of their percoid an- 

 cestors and that a reduction in head spines within 

 a genus was a derived character state. Both M. 

 achne and M. pacificus of the North Pacific have 

 prominent occipital spines (Hagerman 1952; 

 Okiyama andTakahashi 1976) while M. kitt of the 

 northeast Atlantic reportedly has none (Russell 

 1976; Evseenko 1979). This tends to offer support 

 for the concept of a North Pacific origin of the 

 genus Microstomus with M. kitt being a more 

 specialized, derived form. All three species of 

 Glyptocephalus reportedly have preopercular 

 spines (Ahlstrom and Moser 1975; Russell 1976; 

 Okiyama^) although total number and relative 

 size have not been well documented for each 

 species. It would be interesting to see if a reduction 

 in preopercular spination occurs in G. cynoglossus 

 of the North Atlantic, following a pattern similar 

 to M. kitt. 



Both egg size and size at transformation reach 

 maxima in species of this generic complex in the 

 northeast Pacific. Eggs of E. bathybius are about 

 3.0 mm in diameter and those of M. pacificus and 

 G. zachirus are >2.0 mm (Pearcy et al. 1977). 

 Larval lengths of up to 89 mm in G. zachirus and 

 65 mm in M. pacificus prior to transformation 

 have been reported (Pearcy et al. 1977). The latter 

 species develops an extremely deep bodied, highly 

 compressed specialized larval form. The large egg 

 size and size at transformation may possibly re- 

 flect an environmentally induced, specialized 

 adaptation to the upwelling system (or deep 

 habitat in the case of E. bathybius) and asso- 

 ciated circulation patterns of the region. 



Patterns of eye migration in relation to caudal 

 fin development vary among genera. In G. 

 zachirus the caudal fin forms entirely before the 

 left eye begins to migrate whereas in M. pacificus, 

 the eye begins to migrate as notochord flexion be- 

 gins (Pearcy et al. 1977). Relatively few specimens 

 of G. zachirus have been collected with the left eye 

 on the middorsal ridge suggesting that once eye 

 movement is initiated it proceeds rapidly, with 

 transformation completed shortly thereafter. This 

 is in contrast to M. pacificus where a large number 

 of specimens in a wide size range (10-63 mm SL) 

 have been collected with the eye on the middorsal 



■"M. Okiyama. Professor, Ocean Research Institute, University 

 of Tokyo, 1-15-1, Minamidai, Nakano-ku, Tokyo 164, Japan, pers. 

 commun. April 1979. 



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