Geotria macrostoma (Burmeister, 1868)
photo by Scarlato, N.

Family:  Geotriidae (Southern lampreys)
Max. size:  62.9 cm TL (male/unsexed)
Environment:  demersal; freshwater; brackish, unknown
Distribution:  South America and Southwest Atlantic Islands: De la Plata River, Uruguay; de la Plata River to Tierra del Fuego, Argentina; Malvinas (Falkland) Islands, South Georgia. One record in a river tributary of Magellan Strait in Chile.
Diagnosis:  This species is distinguished from G. australis by having a second dorsal fin connected with the caudal fin by a low skin fold (vs. separate), and by the position of the cloaca posterior to the origin of the second dorsal fin in immature and mature adults (cloaca anterior to or under the origin of the second dorsal fin); while the position of fins and cloaca of mature G. macrostoma remains similar to that of juvenile and sub-adults, in spawning adults of G. australis the separation between the second dorsal fin and the caudal fin becomes reduced to a notch (Ref. 125560).
Biology:  Length of sub-adult individuals 41.2-62.9 cm TL (Ref. 125560).
IUCN Red List Status: Least Concern (LC); Date assessed: 06 May 2022 Ref. (130435)
Threat to humans: 


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