FISHERY BULLETIN: VOL. 75, NO. 4 



tenna for the reception of water displacement and 

 low frequency sound. In this connection it may be 

 pointed out that in the related Stylephorus chor- 

 datus the lateral line is continued onto the exceed- 

 ingly elongated caudal filament (R.H. Rosenblatt 

 pers. obs.). Stylephorus has tubular eyes directed 

 forward, and it is assumed that it maintains a 

 vertical posture in the water (Marshall 1971:44). 

 That elongate bodies in deep-sea and pelagic fishes 

 are related to a sensory function has been 

 suggested by Wynne-Edwards (1962:80). 



Our presumption is that adult Desmodema 

 hover vertically, visually seeking prey silhouetted 

 against downwelling light. The lateral-line sys- 

 tem of the tail would be used to sense predators 

 approaching beneath the field of view of the eyes. 

 Undulations of dorsal fin would be used for 

 position-holding and the lateral body musculature 

 used for burst swimming for prey capture and pre- 

 dator avoidance. 



This mode of life may predominate in the elon- 

 gate trachipteroids. Nishimura (1963) has infer- 

 red a similar life-style for Trachipterus ishikawai. 

 Adults of Zu cristatus have a long, thin tail, re- 

 miniscent of that of the species of Desmodema, and 

 Clarke and Haedrich (in Gaul and Clark 1968) 

 recorded the following observation: "A large 

 oarfish, Regalecus glesne, was sighted at about 

 210 meters. It was hanging vertically in the water, 

 head up, and appeared to be almost two meters in 

 length .... The dorsal fin was moving continu- 

 ously with wave-like motions progressing from 

 the head end to the tail end, very much like the fin 

 motions seen in file fish." 



Distribution. — Desmodema poly stictum is prob- 

 ably circumtropical, and D. lorum appears to be 

 restricted to the northern Pacific (Figure 2). The 

 most obvious feature of the distributions is the 

 lack of sympatry. Desmodema polystictum is 

 broadly distributed in the tropical Pacific; the 

 northern and southernmost records for the species 

 are in areas influenced by warm currents. Des- 

 modema lorum on the other hand is mostly re- 

 stricted to the cooler waters of the North Pacific. 

 Twenty of the 21 eastern Pacific specimens were 

 taken north of lat. 28 °N, that is in areas north of 

 the 20 °C August surface isotherm and the 9°C 

 200-m isotherm. The single western Pacific cap- 

 ture (a metamorphosed juvenile) was in the area 

 where the temperature at 200 m is about 16°C. 



The only area of possible sympatry indicated is 

 near Cape San Lucas, lower California, where 



there are several records of D. polystictum and a 

 single record of D. lorum. Occurrence of the latter 

 that far south may be related to transport by the 

 California Current. 



From Figure 2 it appears that both species of 

 Desmodema are especially common in the eastern 

 Pacific. The pattern of captures more likely 

 reflects effort. Many of the specimens of D. poly- 

 stictum have been taken incidentally by the purse 

 seine tuna fishery, w r hich is concentrated in the 

 eastern tropical Pacific. Similarly the predomi- 

 nantly eastern records for D. lorum probably 

 reflect the intensive collection effort in the region 

 of the California Current. 



The presence of D. polystictum in the Atlantic 

 rests on the records of Leapley ( 1953) and Walters 

 (1963). G. Krefft, Instit fur Seefischeri, Hamburg, 

 has informed us that the RV Walter Her wig has 

 taken several specimens of Desmodema in the 

 central and southern Atlantic, but that the mate- 

 rial is not available for study at the present time. 



Comparison and relationships. — Walters and 

 Fitch (1960) distinguished Desmodema from 

 Trachipterus primarily on the basis of the nature 

 of the caudal fin (parallel to the body axis), the 

 length of the gastric caecum (long), the absence of 

 sharp-tipped midventral tubercles, and the pre- 

 sence of scales in Desmodema. The last character 

 is not diagnostic, since our study indicates that D. 

 polystictum lacks scales at all sizes. The caudal 

 structure of Desmodema is unique in the Trachip- 

 teridae in that all of the caudal rays are borne on 

 the terminal centrum and the hypural of the first 

 ural centrum is ray less (Figure 1). Additionally, in 

 the species of Desmodema there are seven 

 pterygiophores before the first neural spine and 

 one or two between the first and second neural 

 spines, and in Zu and Trachipterus there is a 

 single pterygiophore before the first neural spine, 

 and nine between the first and second neural 

 spines. 



Walters (1963) regarded Zu as the most 

 generalized and Desmodema as the most 

 specialized of the three trachipterid genera. De- 

 spite the specializations unique to Desmodema 

 and Zu respectively, present evidence indicates 

 that the two genera are more closely related to 

 each other than either is to Trachipterus . The 

 most important indicator of relationship if the 

 presence in both of the dermal tubercles in large 

 prejuveniles, and tubercles and a cutaneous pore 

 system in juveniles and adults. Dermal tubercles, 



846 



