RAJU: THE GENUS MONOGNATHUS 



Description: Specimen described (SIO 66-353): 

 Body deep, compressed except at head, total 

 length 30 mm. Maximum depth in middle of 

 body, 3.8 in total length. Posterior end of body 

 attenuate, caudal organ not yet developed. Head 

 short, 7.5 in total length. Skull membranous and 

 transparent. Snout short, 4.0 in head. Olfactory 

 organ rudimentary. Eyes round, dark brown, 5.7 

 in head. Upper jaw soft, maxilla indistinct. Lower 

 jaw partly damaged. Teeth six in upper jaw, five 

 in lower jav/. Gill opening small, four gill arches. 

 Pectoral fin small, thick. Esophagus a narrow 

 tube, reaching middle of body. Stomach rudi- 

 mentary. Intestine short, swollen, looped. Liver 

 a small ventral lobe. Pancreas rectangular, 

 dorsal to gut. Opisthonephros a short tube. 

 Myotomes 45 + 125 = 170. 



Pigmentation: Minute dark brown chromato- 

 phores on swollen part of intestine. 



LEPTOCEPHALUS PSEUDOLATIS- 

 SIMUS BERTIN 1934 



Figure 4D 



Leptocephalus gastrostomi bairdii Lea 1912. 

 Leptocephalus pseudolatissimus Bertin 1934. 

 Material examined: SIO 56-127, Marshall Islands 

 vicinity, western Pacific, 1(32 mm). 



Description: Body deep, compressed except at 

 head, posterior end tapering. Maximum depth in 

 the middle of body, 4.0 in total length. Head 

 large, very deep, 7.6 in total length. Skull bones 

 transparent and membranous. Teeth in both jaws 

 lost due to damage. Gill opening small, gill 

 arches five in number. Pectoral rudimentary. 

 Esophagus a narrow tube. Stomach small. Liver 

 a small ventral lobe. Pancreas rectangular. Opis- 

 thonephros a short tube. Myotomes 38 + 65 = 103. 



Pigmentation: Dense brown pigmentation in 

 the form of small patches on the swollen part 

 of the intestine. 



Figure 4. — A, leptocephalus of Cyema atrum; B, unknown 

 Pacific leptocephalus; Bl, head of unknown Pacific leptoce- 

 phalus; C, Leptocephalus latissimus; D, Leptocephalus pseudo- 

 latissimus; E, leptocephalus of Nemichthys scolopaceus. Gb, 

 gall bladder; Gl, gills; Go, gill opening; In, intestine; Lr, 

 liver; Op, opisthonephros; Pf, pectoral fin; Sp, suspensorium; 

 ' St, stomach; Th, thyroid gland?; Pn, pancreas. 



Remarks: Leptocephalus latissimus and L. 

 pseudolatissimus resemble each other in many 

 characters except for the differences in myotomal 

 count, number of gill arches, length and number of 

 intestinal loops, and pigmentation. L. latissimus 

 has a higher myotomal count ranging from 170 to 

 250 and four gill arches whereas L. pseudolatis- 

 simus has 103-125 myotomes, five gill arches, a 

 short intestinal loop, and more pigmentation on 

 the loop. 



Murray and Hjort (1912) discovered the lep- 

 tocephalus stage in the life history of Sacco- 

 pharyngiformes. The larva was later described 

 by Lea (1913), who named it Leptocephalus gas- 

 trostomi bairdii (Gastrostomus bairdii = Eury- 

 pharynx pelecanoides) and suggested that L. 

 latissimus Schmidt (1909, 1912) was a larva of 

 another saccopharyngiform. Bertin (1938) de- 

 scribed a series of four saccopharyngiforms and 

 assigned both L. latissimus and L. pseudolatis- 

 simus to Saccopharynx on the basis of the nature 

 of suspensorium and myotomal counts. The lowest 

 myotomal count in his larvae was 115, and since 

 the highest vertebral count of Eurypharynx 

 known to him at that time was 110, he assigned 

 the larvae to Saccopharynx as the number 

 exceeded the highest vertebral count of Eury- 

 pharynx. It is now known that the vertebral 

 count of £. pelecanoides ranges from 103 to 125 

 (Orton, 1963). Tchernavin (1947a) disputed 

 Bertin's allocation of larvae of Saccopharynx on 

 the basis of myotomal count and suggested that 

 the low count forms might belong to Eurypharynx 

 and the high count forms to Saccopharynx. Orton 

 (1963) and Bohlke (1966) also suggested the 

 identity ofL. pseudolatissimus with Eurypharynx 

 on the basis of vertebral counts (97-125). 



METAMORPHIC FORM OF 

 SACCOPHARYNX 



(Not illustrated) 



LACM 9579-36, 30^00'00"N-29^30'21"N, 

 118°40'59"W-118°29'18"W, 2,910 mwo, IKMT, 

 1(80 mm), 30 Aug. 1966. 



Description: Body elongate, posterior region 

 whiplike. Head large, depressed, 14.3 in total 

 length. Snout small, 4.7 in head. Olfactory organ 

 small, two nostrils placed closely one above the 

 other in front of eye. Eye small, 7.0 in head. 



557 



