330 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 169. Ceratioid larvae. (A-B) Himantolophidae. (A) Himantolophus groenlandicus gr., female, 6.0 mm; (B) Himanlotophus alhinares gr., 

 male, 7.1 mm; (C-D) Melanocetidae; (C) Melanocelus Ijohnsoni. female, 12.0 mm; (D) Metanocetus murrayi. male, 6.0 mm; (E) Diceratiidae, 

 Diceralias sp., metamorphic female, 10.5 mm; (F) Thaumatichthyidae, Thauinalichlhys sp., female, 6.4 mm. (All from Bertelsen, 1951.) 



dwarfed, lack an external illicium, and are furnished with den- 

 ticular teeth adapted to attach to the female. 



We may assume an ogcocephalid or chaunacid-like ancestral 

 ceratioid which, from the benthic and littoral environment of 

 its ancestors, has invaded the bathypelagic zone of the ocean. 

 Probably this evolution has passed through forms in which the 

 adults were benthic, while the juveniles after metamorphosis 

 continued the pelagic life of the larvae during adolescence as 

 for instance found in the family Chaunacidae and as retained 

 or reestablished in the ceratioid genus Thaumatichthys. This 

 move to a new adaptive zone has led to a dimorphism which 

 separates the tasks of the two sexes, the females obtaining ad- 



aptations to the bathypelagic conditions of the lophiiform feed- 

 ing strategy by passive luring, the males being adapted solely to 

 active search for a sexual partner. In both sexes the change from 

 benthic to pelagic life has induced a number of changes of which 

 the most important are: loss of the pelvic fins; a change of the 

 position and development of their limb-like pectoral fins, now 

 used for counteracting gravity during swimming rather than for 

 support and movement on the bottom; and a general trend to 

 reduce their density by reduction of bony structures and by 

 retaining the thick subdermal layer of gelatinous tissue present 

 in the larvae. In the latter character and in the position and 

 shape of the pectoral fins, they may be regarded as neotenic as 



