Developmental anatomy of lampreys.

Lampreys are a group of aquatic chordates whose relationships to hagfishes and jawed vertebrates are still debated. Lamprey embryology is of interest to evolutionary biologists because it may shed light on vertebrate origins. For this and other reasons, lamprey embryology has been extensively researched by biologists from a range of disciplines. However, many of the key studies of lamprey comparative embryology are relatively inaccessible to the modern scientist. Therefore, in view of the current resurgence of interest in lamprey evolution and development, we present here a review of lamprey developmental anatomy. We identify several features of early organogenesis, including the origin of the nephric duct, that need to be re-examined with modern techniques. The homologies of several structures are also unclear, including the intriguing subendothelial pads in the heart. We hope that this review will form the basis for future studies into the phylogenetic embryology of this interesting group of animals.