Evans, T.M., Janvier, P. & Docker, M.F. The evolution of lamprey (Petromyzontida) life history and the origin of metamorphosis. Rev Fish Biol Fisheries 28, 825–838 (2018). https://doi.org/10.1007/s11160-018-9536-z

The main focus of this paper is the development of the life history of the lamprey (Petromyzontida) and the beginning of the metamorphosis. Since modern lampreys (Petromyzontiformes) are one of only two lineages of jawless fish that have survived (agnathans), they are crucial to comprehend the evolution of vertebrates. The origin of their multi-stage life history is unknown, despite the fact that their fossil record is scant. Despite this, it appears they have been morphologically conserved for at least 360 million years. All modern lampreys have a complex life cycle that includes a long-lived freshwater larval (or ammocoete) phase, followed by a true metamorphosis into a sexually-immature juvenile and then a mature adult, which differ dramatically in their morphology and ecology from the larva. This is in contrast to hagfishes, the other extant group of jawless fishes, which exhibit direct development. Since they are at the base of the food chain, it is crucial to know when the current life history of the lamprey developed and whether it was present in the last common ancestor of agnathans and gnathostomes.

Recent advancements in developmental biology, genetic studies, and paleontology are shedding light on this issue. These results are summarized in the current review, which comes to the conclusion that the ancient lamprey life cycle involved direct development. We propose that the larval period, if it existed at all, was brief and very limited, but that the juvenile comprised aspects of modern larvae. During evolution, multiple selection pressures acting over the span of the lifetime formed distinct larval and juvenile/adult eras. To accommodate the significant changes in the body plan and to maximize the effectiveness of each life period, each period requires the radically varied morphologies found in modern lampreys.

1. A) How are these findings unique/new/unusual? Lampreys were around 360 million years ago, long before the dinosaur era, and their morphology has remained almost unaltered across hundreds of millions of years of evolution, according to fragmentary fossil discoveries. That is mind-blowing.

1. B) How do these results relate to fields you are personally interested in? The interesting facts and how we can figure out something was introduced millions of years before we were even created is crazy and makes me want to dive into it deeper and see what else I can find.

The superclass Agnatha includes a group of fish known as lampreys that resemble eels but lack a jaw. The phylogenetic links of this group of living vertebrates thought to be among the most archaic have been the focus of extensive study and discussion. Lampreys are believed to be most closely related to hagfishes, another genus of jawless fish, based on molecular and morphological evidence. The clade Cyclostomata, which includes jawed fish, lampreys, and hagfishes together, is thought to be the sister group to all other living vertebrates (gnathostomes).

There are currently 41 recognized species of lampreys (Petromyzontiformes), one of the two remaining groups of agnathan (jawless) vertebrates. The 37 species of Northern Hemisphere lampreys belonging to this group have an anti-tropical distribution, while the four species of Southern Hemisphere lampreys are divided into either the Geotriidae (one species) or Mordaciidae (three species). Recent genetic investigations have shed light on these species’ evolutionary history while the phylogenetic relationships among them are continuously being investigated and amended. Study into the lamprey phylogeny is still underway, and these investigations shed light on the evolutionary links of these amazing and old species.

Lampreys and gnathostomes have been identified as the closest relatives by morphological cladistic analysis, however, molecular phylogenetic investigations have recovered a monophyletic Cyclostomata (hagfish and lampreys as closest relatives). Most lamprey species are parasitic on other fish and are distinguished by their toothed, funnel-shaped sucking mouth. The other tetrapods and the cartilaginous and bony fishes are classified as gnathostomes. Sharks, rays, skates, and ghost sharks are among the fish that are cartilaginous. The Phylogemic tree is a great representation of the lamprey’s closest relative and represents evolutionary relationships among organisms.

Sources: 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3995830/#:~:text=Lampreys%20are%20a%20group%20of,group%20of%20the%20jawed%20vertebrates. 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3995830/#:~:text=Lampreys%20are%20a%20group%20of,group%20of%20the%20jawed%20vertebrates.

The graphic above displays some internal anatomical features of the sea lamprey, Petromyzon marinus, the species I chose for my blog.

The “eel-like” body of the Petromyzon marinus is often split into three regions: the head, which extends forward from the branchial (gill) area; the caudal region, which extends rearward from the vent; and the trunk region, which is the lamprey’s main body between the gill and vent openings. Lampreys have essential appearance traits, and their tissues and organs can represent the early stages of vertebrate evolution and development. They lack jaws for predation. Did you know lampreys are one of the only survivors of this group of jawless fish? Instead of biting jaws, these eel-like fish have an essential spherical mouth. To adhere to fish, penetrate the skin, and drain the fish’s body fluids, the juvenile sea lamprey employs its suction disk mouth, which is filled with small sharp, rasping teeth and a file-like tongue. A unique feature of lamprey physiology is their comparatively limited ability to detoxify the lampricide TFM, a phenolic chemical used to treat streams infested with larval sea lamprey but has little effect on non-target animals. The Sea Lamprey is truly an amazing creature.

https://www.sciencedirect.com/science/article/pii/S0380133021002343#:~:text=A%20novel%20feature%20of%20lamprey,et%20al.%2C%202021).

https://www.dec.ny.gov/animals/7242.html#:~:text=The%20juvenile%20sea%20lamprey%20uses,drain%20the%20fish’s%20body%20fluids.