RAJU THE GENUS MONOGNATHUS 



larvae described in this account help to identify 

 L. latissimus as the larva of Saccopharynx. 

 Bohlke (1966) pointed out that the similarities 

 between saccopharyngids and monognathids 

 might warrant consideration of monognathids as 

 postlarval saccopharyngids. The characters of the 

 metamorphic Saccopharynx and M. isaacsi do not 

 support his contention. The ethmoid tooth persists 

 into the fully transformed stage in monognathids 

 (M. isaacsi), but it is absent in the metamorphic 

 Saccopharynx. A girdlelike region is present on 

 the esophagus, and the liver is a short lobe in 

 monognathids, whereas no girdlelike region is 

 present; the liver is elongate, and the tail is 

 extremely attenuate and whiplike in meta- 

 morphic Saccopharynx. 



A new type of saccopharyngiform larva has 

 been recently studied (Castle and Raju, unpub- 

 lished data), and the details will be published 

 elsewhere. This larva (myotomes 62 + 43 = 105) 

 resembles L. latissimus and L. pseudolatissimus 

 in the shape of the body, myotomes, and other 

 features, but differs from them in having a large 

 eye, absence of long needlelike teeth in the upper 

 jaw, and the structure of the intestine. At present, 

 it is not possible to assign the larva to any of the 

 known families of the Saccopharyngiformes. 



UNKNOWN PACIFIC 

 LEPTOCEPHALUS 



Figure 4B 



Holotype: SIO 70-118, 24°33'S, 154°55'W- 

 154^56'W, IKMT, 1(40 mm), 4 Oct. 1969. 



Description: Body elongate, compressed ex- 

 cept at head, tapering toward both ends of body. 

 Maximum depth in middle of body, 3.2 in total 

 length. Head long, 3.6 in total length. Snout long, 

 about 4.0 in head. Olfactory organ small, an 

 elongate cup, nostrils not formed. Eye fairly large, 

 13.7 in head, round, black, surrounded by a trans- 

 parent area. Upper jaw elongate, maxilla distinct, 

 dentition 1 + 11. Lower jaw elongate, slightly 

 projecting beyond upper jaw, dentition 1 + 7. 

 Suspensorium long. Gill opening wide. Opercular 

 elements present, cartilaginous. Gills very small, 

 four. Branchiostegals absent. Myotomes wide, 

 V-shaped, 56 + 46 = 102, muscle fibers very 

 broad. Dorsal fin origin on myotome 38, fin rays 

 not formed, predorsal distance 2.0 in total length. 



Anal fin rays not formed. Pectoral fin small, 

 behind gills. Esophagus a straight tube. Stomach 

 a rudimentary, fingerlike process at myotomes 

 17-19. Intestine long, muscular, thrown into three 

 loops of increasing depth posteriorly opening to 

 exterior at myotome 56. Liver small. Gall bladder 

 and stomach enclosed by liver. Pancreas a small, 

 thick lobe. Opisthonephros tubular, wavy, open- 

 ing behind vent. First and last blood vessels to 

 viscera at myotomes 8 and 48, respectively. 



Pigmentation: A thick black patch at tip of 

 lower jaw, a small black patch at tip of upper 

 jaw on ventral side. Sparse black pigment 

 along midline of snout and olfactory region, a 

 series of midlateral patches, one each on myo- 

 tomes 13, 25, 40, 50, 59, the last patch on right 

 side and the rest on left, two stellate melano- 

 phores on dorsal finfold, and a series of five on 

 heart, liver, and intestinal loops on ventral side. 



Remarks: This is the first report of this type 

 of larva from the Pacific. It appears that there is 

 only one record of a similar larva, L. holti, from 

 the North Atlantic off the coast of northern Spain 

 (Schmidt, 1909). L. holti resembles this larva in 

 most characters such as the shape of the body, 

 head, and snout, in dentition, myotomes, gut, 

 liver, and pigmentation. The preanal and total 

 myotomal counts (67 + 45 = 125 + ca) ofL. holti 

 are higher than the myotomal counts of this larva, 

 which undoubtedly belongs to a different but 

 closely related species. 



Schmidt did not allocate L. holti to its adult, 

 but simply suggested that it may belong to some 

 southern warm-water eel. Although it is difficult 

 to establish the identity of the larva conclusively 

 in the absence of successive metamorphic and 

 juvenile stages, certain morphological and ana- 

 tomical characters of the larva are closer to the 

 larval features of Cyema, saccopharyngids, and 

 monognathids, and a comparison of its characters 

 is made with their larval features. 



Comparison with Cyema: This larva has 

 striking resemblances to that of Cyema in the 

 following features: The shape and the size of the 

 body are similar although less deep; the head is 

 elongate; the teeth are similar in shape; the eye 

 is larger and circular; the myotomes are V-shaped; 

 the intestine is thrown into loops; the gill open- 

 ing and gills are small. But the larva differs from 



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