Hyperoarthia

The hyperoartians (Hyperoartia or Petromyzonti) are a class of agnathans (animals without jaws), popularly known as lampreys. They are externally similar to eels, although they are not related to them; They have a gelatinous, cylindrical body, without scales and very slippery. Despite sharing many characteristics with fish, taxonomically they are not included in this group but rather form an independent and very ancient group, placing themselves at the base of the origin of vertebrates. They are marine or freshwater. They are ovoviviparous.

Together with the hagfish and several groups of extinct jawless fish they formed the paraphyletic group of the agnathans. However, new genetic studies have found that lampreys are more related to hagfish than to gnathostomes, forming the Cyclostomi clade. This grouping requires excluding lampreys from the Cephalaspidomorphi clade, which would be jawless fish closer to gnathostomes..

Features

Lampreys have a circular, suction-shaped mouth to attach themselves to the prey they feed on. They have several concentric circles of horny teeth, in addition to a horny tongue used to scrape tissues. These characteristics allow them to scrape the flesh and sip the blood of animals as diverse as sharks, salmon, cod, and marine mammals. They are equipped with a tongue that works like a plunger: after making a vacuum on the abdomen of a prey inside its mouth, it sucks the blood as it retreats.

Nervous system

Given that there are no references or fossil records of the first vertebrate with a defined central nervous system, the species of the class Hyperoartia have been used as a reference for the study of the evolution of said system. This is because they constitute the phylogenetically oldest current species of vertebrates, whose origin dates back to approximately 470 million years ago, and their nervous system could be considered an intermediate step between that of invertebrates and the rest of vertebrates.

Its nervous system maintains the rostrocaudal polarization that already appears in invertebrates, maintaining a similar organization. This is because in the case of both vertebrates and invertebrates this organization depends on the same orthologous homeogens (chd and bmp-4 in the case of the former. and sog and dpp in the latter). Another similarity between lampreys and invertebrate chordates is that the axons of their neurons are not myelinated, which means that the speed of transmission of their nervous impulses is very low, that is, approximately 10-20 m/s compared to 120-150 m/s of a myelinated axon.

The cerebral hemispheres of lampreys are not particularly developed. Basically, its function is reduced to the processing of olfactory information from the olfactory bulbs, which it receives through the neuronal connections established with the epithalamus and hypothalamus. This olfactory information allows it to control predation and reproduction behaviors.

In lampreys the general basic organization of the central nervous system of vertebrates can already be observed. In their spinal cord and brainstem, lampreys also have dorsoventral functional specialization similar to that of vertebrates. This means that if we transversely sectioned any of these two regions, the sensory functions would be concentrated in the dorsal area and the motor functions in the ventral area. This anatomical scheme is maintained in all current vertebrates, which reveals the homology that exists between various brain regions of the different species although, evidently, the selective pressure of the ecological niches that each of them occupies has caused notable changes in the function and structure of these regions.

Beyond its similarities with that of invertebrates, the central nervous system of lampreys stands out for its regenerative capacity. It has been shown that after being transversely sectioned, the spine is capable of recovering, regenerating its axons and being able to once again perform the functions prior to the injury. Studies suggest that this regeneration is due to a neurogenesis process, although there is still not enough scientific evidence to prove it.

Taxonomy

The Hyperoartia include modern lampreys and their most immediate ancestors; All current species, about 40, belong to the order Petromyzontiformes:

• Order Euphanerida

• ?Legendrelepis †

• Order Petromyzontiformes

• ?Hardistiella †
• Mayomyzon †
• Mesomyzon †
• ?Pipiscius †
• Priscomyzon †
• Family Geotriidae

• Geotria

• Geotria australis (J. E. Gray, 1851) (Package floor, or wide-mouth)
• Geotria macrostoma (Burmeister, 1868) (Gran Buenos Aires)

• Family Mordaciidae

• Mordatia

• Mordacia lapicida (J. E. Gray, 1851) (Chile)
• Mordax mortality (J. Richardson, 1846) (Australian street)
• Mordacia praecox (Potter, 1968)

• Family Petromyzontidae

• Entosphenus

• Entosphenus tridentatus (Richardson, 1836) (Pacific)

Fishing

They are caught in rivers, with a harpoon or snoop or, better, to avoid death and blood loss, in places equipped as "fishing grounds" in which, using masonry walls or wooden traps, the waters are channeled to pass through traps called "butrones". In Bajo Miño and the Ulla River, unique constructions called "pesqueiras" Located on both sides of the river in the form of parallelepipeds built of stone that penetrate the riverbed from both banks and whose function is to capture different fish species, including the lamprey. These works, built from granite ashlars aligned obliquely to the course of the river, create the currents that will facilitate the path for the fish to follow on their migratory route against the current for spawning. The construction complex is made up of several bodies called "poios" which leave between them some narrow alleys, between which conical nets like pots or "butrons" will be located. Pesqueiras or fishing are already mentioned in documents from the 12th century although, probably, many of them date back to Roman times..

The ban ends when the month of January arrives and the fishing period ends in the month of May. Lampreys were abundant in all the rivers of Galicia, but today they have already disappeared from many of them. Those of Arbo continue to enjoy well-deserved fame, which celebrates the oldest gastronomic festival in Galicia in their honor, but also those of Nieves, Salvatierra de Miño, Tuy and throughout the Miño River basin located below the A Frieira reservoir between Spain and Portugal, where they are also fished, as happens in Melgaço, Monção and Valença.

Uses

Its meat, although tough, is highly appreciated in Galicia (the Romans already considered it truly exquisite). It is made into an empanada, enjoyed stewed in its own blood as a typical dish of Galician cuisine, called lamprey á bordelaise, or cooked after being cured and dried for preservation out of season. fishing. To do this, once cleaned and opened, it is lightly salted, washed and smoked, lightly greased with oil and dried for conservation, keeping it hanging in a dry and cool place until consumption.

It is also used, among other places, in the cuisine of Burgundy (France) and in this case the dish is known as "burgundian lamprey".