Identification of long-preserved specimens reveals the historical geographic range of the Patagonian lamprey Geotria macrostoma (Burmeister, 1868) in southern South America.

The lamprey genus Geotria Gray, 1851 currently includes only two species: G. australis and G. macrostoma. However, taxonomic relationships within the genus have traditionally been ambiguous and difficult to establish due to the extreme changes in morphology, dentition, and coloration that lampreys undergo during their life cycles, particularly during upstream migration and sexual maturation. Consequently, several lamprey specimens held in museum collections have remained unidentified, especially those from Argentina. In this study, a series of morphometric characters were subjected to discriminant function analysis (DFA) to identify the lamprey species collected during 1867-2004 from the de la Plata River and Patagonia. These specimens are housed at the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" in Buenos Aires, the Museo de Historia Natural de Montevideo, and the Naturhistoriska riksmuseet in Stockholm. Based on the proportions of the length of the oral disc, prebranchial, and pre-caudal body regions, and the depth of the trunk, DFA provided conclusive evidence that the specimens corresponded to the recently revalidated G. macrostoma (Burmeister, 1868), which was originally incorrectly named as Petromyzon macrostomus Burmeister, 1868, Exomegas macrostomus (Berg, 1899), Geotria chilensis (Berg, 1895), and Geotria macrostoma f. gallegensis Smitt, 1901, as well as other nontype museum individuals of uncertain taxonomic status. The identifications of these long-preserved museum specimens provided key information on the historical geographic range of Argentinian lampreys and suggest that the disappearance of the species reported from northern localities (the Pampean Region) can be attributed to the degradation of their critical habitats, primarily caused by anthropogenic impact and climate change.

On the invalid resurrection of the lamprey genus Exomegas Gill, 1883.

The lamprey genus Exomegas Gill, 1883, was erected on the assumption that it was distinguishable from Geotria Gray, 1851, by possessing three rather than two cusps on the transverse lingual lamina (TLL). Based on literature review and examination of holotypes and new data, the authors reaffirm that the TLL of Geotria possesses two or three cusps in the adult stage. The reduction or disappearance of the middle cusp at the beginning or during the spawning run constitutes a key feature of Geotria. The resurrection of Exomegas by Firpo Lacoste, Fernández and Scioscia, Journal of Fish Biology, 2021, 1-6, 1507-1512, is therefore unjustified and not supported.

Morphometric and physical characteristics distinguishing adult Patagonian lamprey, Geotria macrostoma from the pouched lamprey, Geotria australis.

The pouched lamprey, Geotria australis Gray, 1851, has long been considered monotypic in the Geotriidae family with a wide southern temperate distribution across Australasia and South America. Recent studies have provided molecular and morphological evidence for a second Geotria species in South America; Geotria macrostoma (Burmeister, 1868). The aim of this study was to determine morphometric and physical characteristics of adult G. macrostoma that further differentiate this re-instated species of Geotriidae from G. australis. The diagnostic features discriminating immature adult G. macrostoma from G. australis when entering fresh water, are distinct differences in dentition, oral papillae and fimbriae counts and differences in coloration. In addition, G. macrostoma display greater growth of the prebranchial region and oral disc and has a deeper body depth and higher condition factor. All current ecological knowledge of the genus Geotria is based on Australasian populations, which may not be applicable to G. macrostoma. To ensure the conservation and protection of the Patagonian lamprey as a re-identified species, further investigations are needed to understand its life history, biology and ecology throughout its range.

Morphology-based taxonomic re-assessment of the Arctic lamprey, Lethenteron camtschaticum (Tilesius, 1811) and taxonomic position of other members of the genus.

The lamprey genus Lethenteron Creaser & Hubbs, 1922 is widespread across Eurasia and North America, but the number and distribution of its constituent species is not firmly established. After a morphological examination of extant type material of the currently recognized species and their synonyms, Lethenteron mitsukurii (Hatta, 1901) is resurrected with Le. matsubarai Vladykov & Kott, 1978 as its junior synonym. Amongst nonparasitic species Le. reissneri (Dybowski, 1869) and Le. mitsukurii are confirmed as present in Japan and the former is also present on Sakhalin. An in-depth study of large samples of nonparasitic lamprey adults from Japan and Sakhalin Island is needed to determine whether the lower trunk myomere (< 66) individuals from these areas represent one or more undescribed species, or Le. mitsukurii, or Le. reissneri, or a mixture of these three alternatives. The material from the Anadyr Estuary identified by Berg (1931, 1948) as Lampetra japonica kessleri has been re-identified as Le. camtschaticum and there is no evidence that Le. kessleri occurs there. Lethenteron reissneri is reported from the Angara River system, Yenisei River drainage, Russia. Lethenteron alaskense Vladykov & Kott, 1978 is provisionally considered to be a junior synonym of Le. kessleri (Anikin, 1905). Petromyzon ernstii Dybowski, 1872, Ammocoetes aureus Bean, 1881, Petromyzon dentex Anikin, 1905, Lampetra mitsukurii major Hatta, 1911, and Lampetra japonica septentrionalis Berg, 1931 are junior synonyms of Petromyzon marinus camtschaticus Tilesius, 1811. A key is provided to adults of the six species recognized as belonging in the genus Lethenteron.

Redescription of the Far Eastern brook lamprey Lethenteronreissneri (Dybowski, 1869) (Petromyzontidae).

Nonparasitic Lethenteronreissneri (Dybowski) is redescribed based on four syntypes (two adults and two ammocoetes) from the Onon and Ingoda rivers, Russia, and 15 topotypic specimens (seven metamorphosing ammocoetes and eight ammocoetes) from the Onon River system, Russia and Mongolia. Posterial teeth were not mentioned in the original description, but Berg (1931) stated that they were sometimes absent, which he later (Berg 1948) changed to usually absent, based on material (some of which we have re-identified as parasitic Lethenteroncamtschaticum) from far outside of the type locality. The latter view has been widely accepted by subsequent authors. Unfortunately, the poor condition of the two adult syntypes did not permit verification of this character. However, a row of posterials was clearly visible in six of the seven topotypic metamorphosing ammocoetes and indicates their usual presence in the species. The first full description of the ammocoetes, including pigmentation, is provided. The present study restricts the distribution of Lethenteronreissneri to the Shilka and Songhua river systems within the Amur River basin, until a more geographically comprehensive study is undertaken. Additionally, in this study, feeding versus non-feeding at the adult stage, are considered to be valid taxonomic characters at the species level.