FISHERY BULLETIN: VOL. 78, NO. 1 



Figure 30. — Geographical distribution of Melanocetus species. Symbols may indicate more than one capture. 



lower depth limit exceeding 3,000 m, but they are 

 commonly found between roughly 500 and 2,500 

 m. Melanocetus johnsoni is most often collected 

 between 500 and 1,500 m. Melanocetus murrayi is 

 a considerably deeper dwelling species; the bulk of 

 the known material was collected between 1,000 

 and 2,500 m (Figure 31). The relatively thin in- 

 tegument (see Description above) and lighter, less 

 well-ossified skeleton of M. murrayi reflects the 

 poorer trophic economies of these greater depths. 

 The remaining species of the genus are so poorly 

 represented in collections that their vertical dis- 

 tributions cannot be estimated. 



EVOLUTIONARY RELATIONSHIPS 



The Melanocetidae appears to be a relatively 

 underived ceratioid family (Bertelsen 1951; 

 Pietsch 1972a, 1976, 1979). The five species are 

 characterized by a confusing mosaic of primitive 

 and derived character states such that an in- 

 terpretation of interspecific phylogenetic relation- 

 ships is difficult. In any case, however, it seems 

 apparent that M. murrayi has split off from the 

 main line of melanocetid evolution and acquired a 

 number of unique features that reflect its most 

 derived position in the genus: 1) depressed 

 cranium, 2) concave vomer, 3) small pectoral fin, 4) 

 tiny escal bulb, and 5) thin integument. Living in 

 considerably deeper strata than its congeners 

 most probably also reflects a derived condition. 



84 



The four remaining species are much more 

 closely related to each other than any is to M. 

 murrayi. Five characters can be used to distin- 

 guish these forms: 1 ) number of lower jaw teeth, 2) 

 longest lower jaw tooth, 3) illicium length, 4) escal 

 bulb width, and 5) escal morphology. Unfortu- 

 nately, all but the last of these characters overlap 

 in variation among the remaining forms of the 

 genus, and, furthermore, the relative primitive- 

 ness of character states among these features is 

 nearly impossible to determine. Melanocetus 

 johnsoni is perhaps derived in having a relatively 

 long illicium, and in having fewer, but longer jaw 

 teeth (see Pietsch 1972b, 1974, 1975). Melanocetus 

 polyactis and M. niger are similar in having rela- 

 tively short jaw teeth, a similar escal morphology 

 lacking anterior and posterior crests, and a sym- 

 patric geographic distribution that is restricted to 

 the Gulf of Panama and adjacent eastern tropical 

 Pacific. Melanocetus eustalus is derived in having 

 an extremely large escal bulb, comparable with no 

 other known ceratioid. 



ACKNOWLEDGMENTS 



We thank E. Bertelsen for critically reading the 

 manuscript and offering valuable suggestions. 

 The following people and institutions provided 

 study material: John R. Paxton (AMS), Alwyne 

 Wheeler (BMNH), William N. Eschmeyer (CAS), 

 Carter Gilbert (FSM), N. V. Parin (lOAN), Nigel 



