The Biology of Australian Lampreys

Abstract

This contribution reviews published data on the biology of the three species of lamprey found in Australia. Geotria australis and Mordacia mordax are anadromous parasitic species, which at the end of their marine trophic phase typically reach lengths of 550–750 and 300–420 mm, respectively. M. praecox is a non-parasitic lamprey, which has almost certainly evolved from a form similar to M. mordax and rarely reaches 160 mm. The distinctive characters of Geotria and Mordacia support the view that these two genera are appropriately placed in different families (Geotriidae and Mordaciidae). Both families diverge in several respects from that containing all extant Holarctic species (Petromyzontidae).The karyotype of both Mordacia species comprises 76 chromosomes, many of which are metacentric, whereas that of Geotria contains approximately 180 largely acrocentric chromosomes. The dentition of the oral disc and tongue-like piston of G. australis and M. mordax is each particularly distinctive and appears well adapted for extracting flesh and blood, respectively, from teleost hosts. The larval intestine of both Australian genera differs from those of Holarctic lampreys in possessing prominent intestinal diverticula, but Mordacia has only a single diverticulum as opposed to the two found in Geotria.The adults of Mordacia are unique in possessing dorsolateral eyes and having neither a parapineal nor a row of mucus-producing oral fimbriae around the oral disc. The first and third of these features may be related to the lampreys’ unusual burrowing habit. The feeding adults of G. australis possess two unique and conspicuous dorsolateral blue-green stripes and a gap between their second dorsal and caudal fins. Ammocoetes of Geotria contain by far the largest amounts of non-haem iron recorded for any vertebrate, mainly due to very large concentrations of iron in the adipose tissue of the nephric fold. These deposits may reflect adaptations to ensure the maintenance of the very high haemoglobin concentration that characterises larval Geotria.Apart from highlighting the differences between the two genera of Australian lampreys, this contribution also details and discusses the results of previous studies on individual Australian species. These include the ecology of the larval, metamorphosing and adult stages, the changes in concentration, weight and fatty acid composition of the lipids during the life cycle, aspects of liver metabolism, the morphology of the pancreas, intestine, heart and cardiovascular chromaffin cell system, the function of catecholamines and the pineal complex, and details of gonadogenesis and sex differentiation.KeywordsChromaffin CellSinus VenosusLarval LifeAnterior IntestineOral DiscThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.