THREE NEW SPECIES OF THE GENUS MONOGNATHUS AND 

 THE LEPTOCEPHALI OF THE ORDER SACCOPHARYNGIFORMES 



Solomon N. Raju* 



ABSTRACT 



Three new species of the genus Monognathus — M. isaacsi, M. ahlstromi, and M. Jesse — are 

 described from the Pacific Ocean, bringing the number of the species to six. M. isaacsi differs 

 from the other species in having a relatively large head and dark brown pigmentation on 

 the whole body. M. ahlstromi has a characteristic paddle-shaped caudal fin, and M. jesse has 

 a lanceolate caudal fin. A key to the six species and their distribution in the Pacific and 

 Atlantic are given. Leptocephali of Monognathus sp. are identified and described for the first 

 time. The status and relationships of the Monognathidae are discussed. 



Metamorphic forms oi Saccopharynx and Eurypharynx are described. The identity of Leptocephalus 

 latissimus to Saccopharynx and ofL. pseudolatissimus to Eurypharynx is confirmed. An unknown 

 leptocephalus closely resembling that of Cyema is described, and the possibility of a new genus 

 in the Cyemidae is suggested. Relationships of the Cyemidae to the Nemichthyidae are refuted, 

 and relationships of the Cyemidae to the Saccopharyngiformes are supported. 



The deepsea gulpers of the order Saccopharyngi- 

 formes (Monognathidae, Saccopharyngidae, and 

 Eurypharyngidae) are among the most curious 

 and extremely modified bathypelgic fishes, and 

 very little is known about them. Bohlke (1966) 

 reviewed the literature on the attempts to relate 

 them to diverse groups of fishes. 



I describe three new species of Monognathus 

 {M. isaacsi, M. ahlstromi. and M. jesse) and four 

 metamorphic stages of Monognathus sp. A key 

 to the six known species of the genus Monogna- 

 thus is given. This is the first record of the family 

 from the southern, central, and eastern Pacific. 

 The three species of Monognathus described by 

 Bertin (1934, 1938) from the Atlantic and Indo- 

 Pacific regions are only juveniles. The lack of 

 adult monognathids even led Bohlke (1966) to 

 suspect that the then known monognathids might 

 be postlarval saccopharyngids. The specimen 

 named as M. isaacsi is in a more advanced 

 stage than any of the other specimens of the six 

 species. Many of its features clearly indicate that 

 this family is distinct from the Saccopharyngidae. 

 A leptocephalus stage in the life history of Mono- 

 gnathus is reported for the first time. Information 

 on the ethmoid tooth, food, and distribution of 

 Monognathus is given. The status and relation- 

 ships of the family Monognathidae to the Sac- 

 copharyngiformes are discussed. 



'Simpson College, San Francisco, CA 94134. 



Two metamorphic forms, one belonging to 

 Saccopharynx and the other to Eurypharynx, are 

 described, and Leptocephalus latissimus Schmidt 

 1912 is assigned to Saccopharynx and L. pseu- 

 dolatissimus Bertin 1934 to Eurypharynx. 



An unknown leptocephalus closely resembling 

 that of Cyema is described from the North Pacific, 

 and the possibility of a new genus in the Cyemidae 

 is suggested. The relationship of the Cyemidae to 

 the Nemichthyidae is questioned, and its relation- 

 ship to the Saccopharyngiformes is supported. 



MATERIALS AND METHODS 



The account is based on the study of one fully 

 transformed juvenile, two early juveniles, and 

 four metamorphic forms of the genus Monogna- 

 thus collected from the central and eastern North 

 Pacific during the Tethys (1960), CalCOFI (1962), 

 and Scan (1969) expeditions. One specimen of 

 Leptocephalus latissimus was obtained from the 

 San Diego Trough (1950) and its metamorphic 

 form off Baja California. A metamorphic form of 

 Eurypharynx pelecanoides was collected from the 

 central North Pacific during the Styx expedition 

 (1968). All the specimens were collected by the 

 10-foot Isaacs-Kidd midwater trawl (IKMT). Total 

 length and body depth were measured with dial 

 calipers, and measurements of head, snout, and 

 eye were taken by ocular micrometer following 

 the methods of Castle (1963). Some specimens 



Manuscript accepted August 1973. 

 FISHERY BULLETIN: VOL. 72, NO. 2, 1974. 



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