FISHER1 BLLLETIN: VOL. 72. NO. 2 

 Table 2. — Number and position of midlateral melanophores in five metamorphic monognathids and Pacific leptocephalus. 



Metamorphic monogna- 

 thids and 



Pacific leptocephalus 



42-mm specimen 



48-mm specimen 



58-mm specimen 



50-mm specimen 



42.2-mm specimen 



Pacific leptocephalus 



Total number 

 myotomes 



31 ^80= 111 



30 + 83=113 



30 + 75 - 1 1 5 



31 -.-82 = 113 



24 +81 = 105 



56 + 46 = 102 



Left side 

 melanophores 



Right side 

 melanophores 



Total number 



melanophores 



(pre + postanal) 



2 + 3 = 5 



1+4 = 5 



1+4 = 5 



2 + 3 = 5 



2 + 3 = 5 



4 +- 1 = 5 



Distribution of chromatophores 



on myotomes 



R = Right. L = Left 



(15-16)R, (29-30)L. (44-45)R, 

 (59-60)R. (67-68)L 



(15-16)R. (32-33)R, (45-46)L, 

 (57-58)R. (67-68)R 



(12-13)L, (31-32)R, (46-48)R, 

 (56-58)R. (70-71)L 



(15-16)L, (28-29)L. (44-45)R. 

 (55-56)R, (67-68)L 



(9-10)R, (27-28)L, (43-44)L, 

 (55-56)L, {67-68)L 



(13-14)L, (25-26)L, (40-41)L, 

 (50-51)L, (59-60)R 



other known leptocephali possess a maxilla with 

 larval teeth until metamorphosis, monognathid 

 leptocephali also possibly have a maxilla bearing 

 larval teeth. Leptocephali of eels characteris- 

 tically lose their larval teeth during metamorpho- 

 sis, and the adult teeth develop after meta- 

 morphosis. Hence it is possible that monognathid 

 leptocephali might have possessed the maxilla 

 with its larval teeth which might have been lost 

 during metamorphosis. Due to the extreme 

 degenerative changes and deossification of the 

 skull the maxilla might have lost its identity 

 and the adult set of teeth failed to develop. 



Median ethmoid tooth: The median ethmoid 

 tooth is a structure unique to the Monognathidae, 

 and its function is not known. It develops during 

 metamorphosis and persists in the adult. It is 

 larger in M. isaacsi than in other species. It is 

 hollow and slightly curved with a minute opening 

 at its sharp tip. There is a pair of glandular 

 masses, one on each side of the tooth. The ethmoid 

 tooth with its gland closely resembles the fangs 

 of a poisonous snake and probably serves a 

 similar function. 



Gills: Only one gill arch is present in the 

 monognathids according to Bertin (1937a). But a 

 close examination of M. ahlstromi and M. Jesse 

 showed four distinct gill arches bearing short 

 foliaceous gill filaments arranged alternately as 

 in Eurypharynx. The gills and gill openings are 

 very small as are those of Eurypharynx and 

 Saccopharynx. 



Pectoral fin: The pectoral fin is absent in 

 the three species described by Bertin (1937a) 

 and in M. ahlstromi. There is a small fleshy 

 pectoral fin in M. isaacsi and M. Jesse. 



Caudal organ: A caudal organ, whose func- 

 tion is much disputed, is present at the tip of the 

 tail in Eurypharynx and Saccopharynx. Although 

 a typical caudal organ is not present in any of 

 the known species of the monognathids, the 

 caudal fin is modified either into a filamentous 

 structure as in M. taningi, or into a flattened 

 structure as in M. ahlstromi and M. Jesse, or 

 is relatively unmodified as in M. isaacsi. 



Food: Fish eggs with a sculptured egg 

 membrane, fish larvae, and copepods were found 

 in the mouth and pharynx of the metamorphic 

 forms, but they might have been taken accident- 

 ally while in the net. 



Distribution (Figure 3): This family has 

 previously been known only from the Atlantic off 

 the coast of North Africa and from the western 

 Pacific (Bertin, 1938). This study shows that it is 

 widely distributed in the whole tropical and sub- 

 tropical belt of the Pacific, and it is likely that 

 the family may also be found in the tropical 

 Indian Ocean. 



RELATIONSHIPS 



Bertin (1937a, 1938) erected the family Mono- 

 gnathidae based on his study of four juveniles. 



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