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

Abstract

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.

Distribution, hosts and long-term decline in abundance of the Patagonian lamprey inferred from diet assessment of albatrosses

“…There are four species of anadromous parasitic lamprey in the southern hemisphere, including the pouched lamprey Geotria australis, previously considered to be the only member of its family (Geotriidae), which appeared to have a very wide spawning distribution; rivers south of 32°S in Australia (including Tasmania), New Zealand, Chile and Argentina (Neira et al 1988). However, environmental DNA (eDNA), and molecular and morphological studies have revealed a cryptic taxon in Argentina, revalidating the original description in 1868 of the Patagonian (or Argentinian pouched) lamprey G. macrostoma (Nardi et al 2020;Riva-Rossi et al 2020;Baker et al 2021, Riva-Rossi et al 2022). This corroborates studies indicating that Geotria populations in Argentina, Chile and Australasia are morphologically distinct (Neira et al 1988), and is in accordance with the suggestion by Potter et al (1979) that, following the direction of the prevailing currents, young adults from Argentina should move south and east in their marine phase, and those from Chile should move north.…”

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

“…It thus elevated Geotria macrostoma f. gallegensis Smitt, 1901, to the species rank without providing distinguishing diagnostic characters. The proposal of Firpo Lacoste et al (2021) to allocate lampreys from Argentina under Exomegas was subsequently refuted by Riva Rossi et al (2022), who clearly demonstrated that the three TLL cups were reduced to two during adult life, which is a key a diagnostic character of Geotria .…”