Jamoytius kerwoodi, is a primitive, eel-like jawless vertebrate found uniquely in an Early Silurian (Llandovery epoch; 444-433 Ma) horizon near Lesmahagow, Scotland. This species is a rare component of a low-diversity dominantly nektonic detritus and herbivorous fauna living over an anoxic bottom and is found at the transition from a marine-influenced, probably brackish-water, deep-water basin to a shallower-water, less saline and likely freshwater basin. In the absence of true teeth, Jamoytius was probably a detritivore or herbivore feeding on Ceratiocaris. Jamoytius may be a direct ancestor of living lampreys, especially as their ectoparasitic mode of life might have evolved from ancestral microphagous filterers or herbivores.

This paper presents results of the experiments performed on a nonconventional and extremely interesting in regard to evolution, creature, the European river lamprey Lampetra fluviatilis (Petromyzontiformes, Cyclostomata), one of the oldest taxa of vertebrates. We present detailed immunocytochemical and electron microscopy analyses of chromosome synapsis, the transcription process, and chromatin dynamics in lamprey prophase I, which is the first time for science. We found that not all chromosomes complete synapsis. Rounded structures were detected in chromatin and in some synaptonemal complexes but their nature could not be determined conclusively. An analysis of RNA polymerase II distribution led to the conclusion that transcriptional reactivation in lamprey prophase I is not associated with the completion of chromosome synapsis. Monomethylated histone H3K4 is localized to meiotic chromatin throughout prophase I, and this pattern has not been previously detected in the animals. Thus, the findings made it possible to identify synaptic and epigenetic patterns specific for this group, and to add new pieces of the puzzle to the discussions of the scientific issues under study. The research on lamprey meiotic chromatin and chromosomal dynamics raises many questions leading to new discoveries.