Belongs within: Cyclostomata.
The Petromyzontidae, lampreys, are eel-like vertebrates with a filter-feeding freshwater larval stage that develops into non-feeding or parasitic, often marine, adults (Bond 1996).
The dangers of indulgence
Published 21 May 2025
History contains a number of records of monarchs who met their demise in unexpected ways. The Roman emperor Carus was killed when his tent was struck by lightning. Béla I of Hungary suffered life-ending injuries when his throne collapsed beneath him. But a certain turn of phrase attends the death of Henry I of England, whose death was attributed to “a surfeit of lampreys”. Overindulgence in his favourite dish during a hunting trip is supposed to have led to a severe illness from which Henry did not recover. But what were the lampreys of which Henry was supposed to have had a surfeit?
The slender, eel-like vertebrates known as lampreys are found in cooler waters of the world, steering well clear of the tropics. Along with the hagfish, they are one of the relatively small number of living ‘jawless fishes’, possessing a funnel-shaped mouth whose opening is surrounded by an oral hood. Lampreys are best known as parasites on other fishes, using teeth on the oral hood to grasp onto prey while the piston-like tongue rasps at the victim’s skin. In some species, their diet is composed of the blood which flows from the resulting wound; in others, the tongue is used to tear of chunks of muscle tissue. However, not all lampreys are such rapacious parasites. The larval stages of lampreys, known as ammocoetes, live as filter-feeders in fresh water, eschewing a carnivorous life style until they metamorphose into maturity. Some species spend their entire lives in fresh water; others migrate down to the sea upon reaching adulthood. In many of those species that do not leave fresh water, adults are short-lived and non-feeding, passing away shortly after breeding.
Phylogenetic analyses, both morphological and molecular, support a deep divide between Northern and Southern Hemisphere lampreys, supporting their assignment to separate families. The more diverse of these is the Northern Hemisphere lampreys in the Petromyzontidae, with about 35 species described to date. The Petromyzontidae are united by the presence in adults of continuous or contiguous dorsal fins, three or four lateral circumoral teeth on each side of the oral hood, the position of the cloaca, and reduction or absence of the gular pouch in males (Gill et al. 2003). Relationships within the petromyzontids have been more unsettled. All indications are that transitions between parasitic and non-parasitic lifestyles have occurred on multiple occasions. The majority of authors have presumed that the original lampreys were anadromous parasites, and that the non-anadromous, non-parasitic habit has arisen repeatedly through neoteny. Brownstein & Near (2023) did claim that their phylogeny supported a non-anadromous, non-parasitic ancestor for petromyzontids as a whole, but I suspect this to be an occasion when inferences were misled by the loss of features being easier than their gain.
Lamprey relationships with humans have run the gamut. As indicated at the top of this post, lampreys have been much prized at times as an eating fish, and remain so in some areas. Conversely, parasitic species have been excoriated as a menace to other fish stocks. The sea lamprey Petromyzon marinus is a particularly notorious example, with its introduction and spread in the North American Great Lakes as result of the construction of shipping canals having a severe impact on species such as trout and whitefish. However, some lamprey species may be threatened or endangered by human activity; non-parasitic species seem to be particularly vulnerable in this regard. One freshwater parasitic North American species, the Miller Lake lamprey Entosphenus minimus, was deliberately targeted for eradication as a supposed threat to trout fisheries, and was for some time thought extinct before its recent rediscovery. Henry I may have suffered from a surfeit of lampreys, but in some areas there is now more cause for concern about their dearth.
Systematics of Petromyzontidae
Characters (Bond 1996): Body eel-like, dorsal and caudal fins present, lacking paired fins or scales; eyes lateral; mouth ventral, consisting of a circular disc set with horny teeth; nasohypophyseal opening between eyes. Skeleton cartilaginous, not well developed except skull and branchial region; vertebral centra absent, neural arches rudimentary. Myotomes not divided into epaxial and hypaxial muscles. Internal labyrinth bearing ciliated epithelium; left duct of Cuvier absent; dorsal and ventral roots of spinal nerves not connected. Gills in adults opening into respiratory tube beginning at mouth, extending under oesophagus, ending at seventh pair of gills; gills in larvae opening into long pharynx that is cut off posteriorly during metamorphosis. Larvae eyeless, toothless.
<==Petromyzontidae [Petromyzonidae] | i. s.: CaspiomyzonB96 | Velasia Gray 1851 [incl. Neomordacia Castelnau 1872]O96 | |--*V. chilensis Gray 1851 [=Geotria chilensis]O96 | `--V. stenostomus [incl. Neomordacia howittii Castelnau 1873, Yarra singularis Castelnau 1873]O96 | Exomegas Gill 1882O96 | `--*E. macrostomus (Burmeister 1868) [=Petromyzon macrostomus]O96 |--Geotria Gray 1851O96 [GeotriinaeB96] | `--*G. australis Gray 1851 [incl. G. allporti Günther 1871]O96 |--Mordacia Gray 1851O96 [incl. Caragola Gray 1851O96; Caragolinae, Mordaciidae, MordaciinaeB96] | |--*M. mordax (Richardson 1845) [=Petromyzon mordax, Caragola mordax]O96 | |--‘Caragola’ lapicida [incl. P. acutidens Philippi 1864, P. anwandteri Philippi 1863]O96 | `--M. praecoxB96 `--PetromyzontinaeB96 |--Petromyzon Linnaeus 1758L58 | |--P. branchialis Linnaeus 1758L58 | |--P. fluviatilis Linnaeus 1758L58 | `--P. marinus Linnaeus 1758FM02 |--EudontomyzonB96 | |--E. danfordi (Regan 1911)SE08 | |--E. mariae (Berg 1931)SE08 | `--E. vladykoviB96 |--IchthyomyzonB96 | |--I. bdelliumB96 | |--I. castaneusB96 | |--I. fossorB96 | |--I. gageiB96 | |--I. greeleyiB96 | `--I. unicuspisB96 `--LampetraB96 | i. s.: L. aepypteraSBW95 | L. fluviatilis (Linnaeus 1758)SS07 | L. kessleri Anikin 1905I92 | L. minimaB96 | L. planeri (Bloch 1784)SS07 | L. richardsoniB96 |--L. (Lampetra) ayresiiH71 |--L. (Entosphenus)H71 | |--L. (E.) lethophaga Hubbs 1971H71 | `--L. (E.) tridentata Richardson 1836H71, I92 [=Entosphenus tridentatusT90; incl. E. tridentatus ciliatusH71] `--L. (Lethenteron)H71 |--L. (L.) appendixSBW95, MS16 |--L. (L.) lamottenii [=Entosphenus lamottenii]H71 |--L. (L.) japonicaH71 [=Entosphenus japonicusSBM11, Lethenteron japonicumPB07] |--L. (L.) reissneriT90, PB07 `--L. (L.) zanandreaiH71
*Type species of generic name indicated
References
[B96] Bond, C. E. 1996. Biology of Fishes 2nd ed. Saunders College Publishing: Fort Worth.
Brownstein, C. D., & T. J. Near. 2023. Phylogenetics and the Cenozoic radiation of lampreys. Current Biology 33: 397–404.
[FM02] Flescher, D., & F. H. Martini. 2002. Lampreys. Family Petromyzontidae. In: Collette, B. B., & G. Klein-MacPhee (eds) Bigelow and Schroeder’s Fishes of the Gulf of Maine 3rd ed. pp. 16–19. Smithsonian Institute Press: Washington.
Gill, H. S., C. B. Renaud, F. Chapleau, R. L. Mayden & I. C. Potter. 2003. Phylogeny of living parasitic lampreys (Petromyzontiformes) based on morphological data. Copeia 2003 (4): 687–703.
[H71] Hubbs, C. L. 1971. Lampetra (Entosphenus) lethophaga, new species, the nonparasitic derivative of the Pacific lamprey. Transactions of the San Diego Society of Natural History 16 (6): 125–164.
[I92] Iwahashi, J. (ed.) 1992. Reddo Deeta Animaruzu: a pictorial of Japanese fauna facing extinction. JICC: Tokyo.
[L58] Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii: Holmiae.
[MS16] McCoy, V. E., E. E. Saupe, J. C. Lamsdell, L. G. Tarhan, S. McMahon, S. Lidgard, P. Mayer, C. D. Whalen, C. Soriano, L. Finney, S. Vogt, E. G. Clark, R. P. Anderson, H. Petermann, E. R. Locatelli & D. E. G. Briggs. 2016. The ‘Tully monster’ is a vertebrate. Nature 532: 496–499.
[O96] Ogilby, J. D. 1896. A monograph of the Australian Marsipobranchii. Proceedings of the Linnean Society of New South Wales 21 (3): 388–426.
[PB07] Philippe, H., H. Brinkmann, P. Martinez, M. Riutort & J. Baguña. 2007. Acoel flatworms are not Platyhelminthes: evidence from phylogenomics. PloS One 2 (8): e717.
[SS07] Schreiber, A., & R. Sosat. 2007. The genetic population structure of the Eurasian fine-scaled minnow, Phoxinus phoxinus (Linnaeus 1758), in the contact area of the upper Rhine and Danube rivers (southwestern Germany) (Osteichthyes, Cypriniformes, Cyprinidae). Senckenbergiana Biologica 87 (2): 195–211.
[SE08] Sevcsik, A., & T. Erös. 2008. A revised catalogue of freshwater fishes of Hungary and the neighbouring countries in the Hungarian Natural History Museum (Pisces). Annales Historico-Naturales Musei Nationalis Hungarici 100: 331–383.
[SBM11] Solomon, E. P., L. R. Berg & D. W. Martin (eds) 2011. Biology 9th ed. Brooks/Cole Cengage Learning.
[SBW95] Stauffer, J. R., Jr, J. M. Boltz & L. R. White. 1995. The fishes of West Virginia. Proceedings of the Academy of Natural Sciences of Philadelphia 146: 1–389.
[T90] Taguchi, S. 1990. Nihon no Sakana. Kogakukan: Tokyo.