THE RIBBONFISH GENUS DESMODEMA, WITH THE DESCRIPTION 

 OF A NEW SPECIES (PISCES, TRACHIPTERIDAE) 



Richard H. Rosenblatt 1 and John L. Butler 2 



ABSTRACT 



The genus Desmodema is unique within the Trachipteridae in that the upper caudal lobe, borne on the 

 second ural centrum, is not upturned, and the lower caudal lobe, borne on the first ural centrum in other 

 trachipterids, is absent, and in that there are seven dorsal pterygiophores before the first neural spine. 

 Desmodema lorum n.sp. can be distinguished from D. polystictum (Ogilby) on the basis of having more 

 vertebrae, fewer caudal rays, a longer tail, and the snout longer than the eye diameter. Desmodema 

 polystictum is probably circumtropical; D. lorum is restricted to the North Pacific Ocean. The species of 

 Desmodema have a distinctive prejuvenile phase characterized by polka dots on the sides, long pelvic 

 fins, a relatively short tail, and elongation of the first six dorsal rays. Metamorphosis is abrupt and 

 involves loss of the pelvic fins, elongated dorsal rays and polka dots, and a great lengthening of the tail. 

 It is suggested that metamorphosis accompanies movement to a deeper habitat. The elongated tail is 

 related to extension of the lateral-line sensory system. On the basis of joint possession of a dermal 

 tubercle and pore system and an abruptly constricted body, Desmodema and Zu are regarded as 

 related. Desmodema, but not Zu, agrees with Regalecus in the arrangement of the dorsal 

 pterygiophores. 



The genus Desmodema was erected for the recep- 

 tion of Trachypterus jacksoniensis polystictus 

 Ogilby (Walters and Fitch 1960). Fitch ( 1964) sub- 

 sequently redescribed Desmodema polystictum, 

 mainly utilizing material from the northeast 

 Pacific, and placed Trachypterus misakiensis 

 Tanaka, 1908 and T. deltoideus Clark, 1938 in its 

 synonymy. Our interest arose from the observa- 

 tion that two recently collected specimens had 

 what appeared to be anomalously low vertebral 

 counts. This initiated the present study, which has 

 revealed the existence of two species, one of them 

 undescribed. In addition to distinguishing and de- 

 scribing the species, our material has allowed us to 

 amplify the generic description of Desmodema and 

 to detail some of the remarkable ontogenetic 

 changes undergone by its species. 



MATERIALS AND METHODS 



Specimens used in this study are housed in the 

 following institutions: California Academy of Sci- 

 ences (CAS), Department of Biology, University of 

 California, Los Angeles (UCLA), Natural History 

 Museum of Los Angeles County (LACM), and 

 Scripps Institution of Oceanography (SIO). In the 



l Scripps Institution of Oceanography, La Jolla, CA 92093. 

 2 Southwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, P.O. Box 271, La Jolla, CA 92038. 



Manuscript accepted March 1977. 



FISHERY BULLETIN: VOL. 75, NO. 4, 1977. 



material list the first length measurement is the 

 snout-vent length (SV), the second the standard 

 length (SL). A single value indicates snout- vent 

 length of a broken specimen. 



Because of the delicacy of the species, most of the 

 specimens were damaged in some way, and not all 

 counts and measurements were made on all 

 specimens. In particular, fin lengths represent 

 minimum measurements, since all fins seem to 

 have been broken to some degree. No specimen 

 appeared to have unbroken pelvic fins. Measure- 

 ments are self-explanatory and were taken with 

 flat-point dividers or dial calipers. Vertebral 

 counts were taken from radiographs or cleared 

 and stained material. Dorsal rays could be enum- 

 erated on only a few specimens. 



RESULTS 



Desmodema Walters and Fitch 



Desmodema Walters and Fitch 1960. Type-species 

 Trachypterus jacksoniensis polystictus Ogilby 

 1897, by original designation. 



Diagnosis. — A trachipterid with 4-10 caudal 

 rays, the caudal on the same axis as the caudal 

 peduncle, all caudal rays borne on terminal cen- 

 trum, no lower caudal lobe. Seven dorsal 

 pterygiophores before first neural spine. Body con- 



843 



