Morphology and ultrastructure of the gills in two Urodela species: Salamandrina terdigitata and Triturus carnifex

Gill morphology and ultrastructure are described for Triturus carnifex and Salamandrina terdigitata with emphasis on differences occurring between two species that inhabit different aquatic biotopes. The morphology and ultrastructure have been studied using light microscopy and both scanning and transmission electron microscopy. The general organization of the gills is similar in the two species and shows the characteristics of Urodela larvae in which the gills consist of three tufts of filaments supported by gill arches III, IV and V. However, some differences are noticeable in the length of the main filament and in the number of secondary lamellae: in T. carnifex, a pond-dwelling salamander, the main filaments are long and rich in secondary lamellae; in the stream-type larva of S. terdigitata, the main filaments are shorter and show a lower number of secondary lamellae, located in its proximal portion. The cellular composition of the gill filament and of respiratory lamellae is different in S. terdigitata: in the gill filament basal cells, pavement cells, ciliated cells, club-shaped cells, mitochondria rich cells (MRCs) and Leydig cells have been recognized, while in the secondary lamellae the last cellular type does not appear. On the contrary, in T. carnifex we observe the same cellular composition in both filament and secondary lamellae.