(1) These data support the concept that variable and J region sequence have been conserved in the evolution of placoderm-derived vertebrates, but that constant regions show much greater phylogenetic variation.
(2) Of over 60 agnathan and fish genera known, only 5 placoderms (Givetian-Famennian) are cosmopolitan.
(3) The only detectable DNP-binding protein in the serum of placoderm-derived vertebrates was immunoglobulin in nature, and of the order of less than or equal to 1% total serum immunoglobulin.
(4) Molecular genetic studies of placoderm derived vertebrates are incomplete but are sufficient to allow the conclusion that Igs of these species are specified by variable (V), joining (J) and constant (C) gene segments and that rearrangement are an essential feature for the generation of antibody diversity.
Placodermi
Definition:
(n. pl.) An extinct group of fishes, supposed to be ganoids. The body and head were covered with large bony plates. See Illust. under Pterichthys, and Coccosteus.