The presence of plasma cells in the lamprey (Agnatha).
D000818:Animals; D000917:Antibody Formation; D005399:Fishes / Q000276:immunology*; D006410:Hematopoiesis; D007668:Kidney / Q000166:cytology; D007798:Lampreys / Q000276:immunology*; D008214:Lymphocytes / Q000648:ultrastructure; D010950:Plasma Cells / Q000648:ultrastructure*