Discussion of Phylogenetic Relationships
Rhynchactis has undergone such a drastic reduction and loss of parts that clearly it is the more derived of the two gigantactinid genera. Within the genus Gigantactis, there are four morphological trends that seem to characterize anglerfish evolution in general (Pietsch, 1972, 1974:87, 88): (1) an increase in the length of the illicium, (2) a decrease in the number of median-fin rays, (3) a loss of jaw teeth, and (4) an increase in morphological complexity of the luring apparatus, in this case, reflected in a general tendency to increase the number of distal filaments of the esca and filaments of the illicium. Giagantactis longicirra appears to be the least derived member of the genus, having the shortest illicium, the greatest number of longitudinal series of dentary teeth, the highest dorsal-ray count, and the least number of distal escal filaments. Members of the G. macronema group (G. macronema, G. microdontis, and G. ios) are the most derived, having the longest illicium, the fewest series and total number of dentary teeth, the lowest dorsal-ray counts, and numbers distal, escal filaments. The remaining species of the genus are more or less intermediate in specialization. Members of the G. vanhoeffeni group, include G. vanhoeffeni, G. meadi, G. gibbsi, G. gracilicauda, and G. paxtoni, are united in sharing a relatively short illicium and a similar escal morphology. Members of the G. gargantua group, including G. gargantua, G. watermani, and G. herwigi, likewise share a similar escal morphology but are also united on the basis of having a relatively long illicium and an elongation of the second and seventh caudal-fin rays.
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