Metamorphosis in the paired species of lampreys, Lampetra fluviatilis (L.) and Lampetra planeri (Bloch) . 1. A description of the timing and stages

Bird, DJ.; Potter, IC.

Zoological Journal of the Linnean Society 65(2): 127-143


ISSN/ISBN: 0024-4082
DOI: 10.1111/j.1096-3642.1979.tb01086.x
Accession: 021338735

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A large number of larval, metamorphosing and adult nonparasitic lampreys, L. planeri, were collected from 3 different rivers and placed in a morphological series. The characteristic changes were then described and used to propose a sequence of stages (1-9). The 1st signs of metamorphosis (stages 1-2), which could occasionally be found as early as late June, are characterized by the eruption and enlargement of the eyes. This is followed by the rapid transformation of the oral hood into an oral disc, and changes in the shape of the pharyngeal region (stages 2-5). Pronounced alterations in body pigmentation, enlargement of the fins and the development of teeth occur during stages 4-6. The vast modifications involved in stages 2-6 take place relatively rapidly in the period between appr. mid-July and mid-Sept. The subsequent changes, which occur more slowly, eventually lead to the production of immature (stage 7) and sexually mature adults (stage 8). Mature males are characterized by the presence of a urinogenital papilla, while the females possess a post-cloacal fin-like fold and greatly distended trunk. Spawning took place between late March and late April with the spent animals (stage 9) dying soon afterwards. The above sequence of stages was then compared with those found in a smaller sample of the parasitic and ancestral species L. fluviatilis. The early metamorphosing stages in both species are apparently indistinguishable but clear differences start to appear at stage 5 when the body surface of L. fluviatilis is assuming a distinct silvery sheen. This trend becomes more marked in stages 6 and 7, at which time the river lamprey also has a more pronounced eye and disc and a slimmer trunk. Stage 7 in L. fluviatilis represents animals migrating to the sea in either the autumn or spring to commence their trophic phase. This stage in L.