106 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



between P. micropinna and P. nimiiis warranted a separate ge- 

 nus for P. nimius. However, McCosker (1977, 1982) demon- 

 strated that Pseudomyrophis and Neenchelys are both valid gen- 

 era and that P. micropinna, P. nimius, P. atlanlicus and an 

 undescribed Pseudomyrophis from the eastern Pacific are con- 

 generic. Dean (1972) indicated that Myrophis frio properly be- 

 longs in the Pseudomyrophis lineage. Evidence from larval mor- 

 phology supports McCosker's (1977, 1982) recognition of 

 Pseudomyrophis and Neenchelys as valid genera, and supports 

 the recognition of P. micropinna, P. nimius, P. atlanlicus, the 

 undescribed Pseudomyrophis from the eastern Pacific, two un- 

 described Pseudomyrophis known only from their larvae in the 

 western Atlantic, one undescribed Pseudomyrophis from the 

 eastern Atlantic known only from its larva and erroneously 

 identified as P. nimius (Blache, 1977), and Myrophis frio as 

 congeneric. Pseudomyrophis larvae are readily distinguishable 

 from all other ophichthid larvae by a combination of the fol- 

 lowing characters: three unconnected liver lobes, undulating gut 

 and nephros, characteristic head shape, and pigmentation 

 (Blache, 1977; Leiby, in press a). Neenchelys larvae differ tren- 

 chantly from Pseudomyrophis larvae in having two, rather than 

 three, unconnected liver lobes, a gut lacking the marked un- 

 dulations seen in Pseudomyrophis larvae, and a much deeper 

 body than any other known ophichthid (Castle, 1 980; this paper. 

 Fig. 56-lower). Studies of adult Pseudomyrophis and Neenchelys 

 have clearly demonstrated that the two genera are more closely 

 related to each other than either is to any other genus ( McCosker, 

 1977, 1982). In the light of this information, the most parsi- 

 monious interpretation of the data on the larval morphology of 

 the two genera is that Neenchelys was derived from Pseudo- 

 myrophis or a Pseudomyrophis-hke ancestor. Pseudomyrophis 

 and all other known myrophin larvae except Neenchelys have 

 three unconnected liver lobes and similar body length to depth 

 ratios. It seems likely, therefore, that larvae of the ancestral 

 myrophin also had three unconnected liver lobes and a similar 

 body length to depth ratio. Neenchelys larval morphology can 

 be easily derived from this proposed ancestral larval morphol- 

 ogy by significantly deepening the body and foreshortening the 

 gut so that one liver lobe is lost. Derivation of Pseudomyrophis 

 larval morphology from a Neenchelys-Wkc ancestor requires a 

 change from the ancestral larval morphology body plan to the 

 Neenchelys larval body plan and a later re-emergence of the 

 ancestral larval myrophin body plan in Pseudomyrophis. 



Benthenchelys cartieri. a highly specialized pelagic eel (Castle, 

 1972) is the sole member of the tribe Benthenchelyini. The 

 larvae of this species have not yet been described, but based on 

 the hypothesized evolutionary history of the Ophichthidae (Fig. 

 55), it seems likely that the larvae of 5. cartieri will have three 

 unconnected liver lobes, a well-developed dorsal fin which mi- 

 grates little during metamorphosis, and a body length to depth 

 ratio that is typical of the Ophichthidae. Discovery of these 

 larvae should help clarify relationships within the Myrophinae. 



The subfamily Ophichthinae contains four tribes (sensu 

 McCosker, 1977); the Ophichthini, Sphagebranchini, Bascan- 

 ichthyini and Callechelyini. The tribe Ophichthini lies at the 

 evolutionary base of the subfamily Ophichthinae, and contains 

 the most primitive, least specialized members of the subfamily. 

 The ancestral ophichthin was probably Ophichthus-hke. The 

 tribe Ophichthini, which contains two lineages, and the tribe 

 Sphagebranchini can be easily derived from the generalized 

 ophichthin character states which are represented in the genus 



Ophichihus (sensu McCosker, 1977). One lineage in the tribe 

 Ophichthini appears to be directly derived from the generalized 

 Ophichthus condition. The genus Echelus has been represented 

 as belonging to its own unique lineage in the Ophichthinae and 

 has been considered the most primitive member of the tribe 

 Ophichthini because in addition to having all the primitive 

 characters of its closest relative Ophichthus. it possesses a well- 

 developed caudal fin. A re-examination of adult Echelus char- 

 acters in conjunction with the larval characters oi Echelus sug- 

 gests, however, that Echelus belongs to the Ophichthus lineage 

 and that the caudal fin of Echelus is either a case of character 

 reversal or paedomorphosis which resulted in Echelus retaining 

 the larval caudal fin rather than losing it, as is apparently the 

 case in all other members of the Ophichthinae. In addition to 

 the generalized genera Echelus. Ophichthus, and Ophisurus, the 

 Ophichthus lineage contains two groups of specialized genera 

 which are closely tied to Ophichthus by a nearly continuous 

 character series. The Pisodonophis-Myrichthys-Cirrhimuraena 

 group differ from the basic Ophichthus body plan by having an 

 increased number of branchiostegals, multiserial dentition, and 

 individual sp)ecializations found in each genus. The second group, 

 containing Mystriophis and seven allied genera, are specialized 

 for the capture of large active prey by having a strengthened 

 suspensorium and enlarged dentition. The close relationship of 

 this group to Ophichthus is emphasized by similar adaptations 

 in some species of Ophichthus (McCosker, 1977). The close 

 relationship of the Ophichthus lineage is further emphasized by 

 the unique positioning of the nephros relative to the anus found 

 in many members of this lineage. Larvae from seven of the 

 fourteen genera in the Ophichthus lineage have been identified. 

 While there is considerable inter- and intrageneric variability 

 in the general morphology of these larvae, five of the seven 

 genera (Echelus. Ophichthus, Ophisurus, Echiophis, and Apla- 

 tophis) are generally characterized by having larvae with a neph- 

 ros which terminates 4-14 myomeres anterior to the anus on 

 the next to last gut loop or between the last and next to last gut 

 loop (Fig. 57-lower). This condition has not been observed in 

 any genera of the Ophichthinae outside of the Ophichthus lin- 

 eage of the Ophichthini. The larvae of Myrichthys, one of the 

 specialized genera in the Ophichthus lineage, has a nephros which 

 terminates above or just anterior to the anus (Leiby, in press 

 a). Blache (1977) identified a series of larvae as Brachysomophis 

 atlanlicus. This series of larvae differs from the larvae of the 

 closely related genus Aplalophis in having the nephros termi- 

 nating above or just anterior to the anus. Larvae of the western 

 Pacific species of Brachysomophis have not yet been identified. 

 Consequently, it is unknown whether this nephric position is a 

 secondarily derived character of the genus Brachysomophis or 

 whether it is limited to the eastern Atlantic species B. atlanlicus. 

 The other lineage to arise from the generalized Ophichthus- 

 hke ancestor contains eight genera including Quassiremus and 

 Malvoliophis (Fig. 55), which are characterized by various re- 

 ductions and modifications of the generalized Ophichthus-Vike 

 condition such as reduced gill arches, cephalic lateralis systems, 

 and pectoral fins. This lineage probably gave rise to the Sphag- 

 ebranchini and subsequent lineages by continued modification, 

 reduction, and specialization of the ophichthin condition 

 (McCosker, 1977). The larvae of the Quassiremus- Malvoliophis 

 lineage are virtually unknown. Leiby (in press) tentatively 

 identified three larvae as Quassiremus produclus, but no other 

 larvae from this lineage have been identified. There is a natural 



