Comparative Fine Structure of the Actinotrichia (Elastoidin) in Developing Teleost and Dipnoi Fish Fins

Abstract

Actinotrichia are part of the fin dermoskeleton. Among Osteichthyes these thin slender tapered rods occupy the free margin of all the developing and adult fins only in Actinopterygii, while in the Sarcopterygii, actinotrichia are only present in the developing fin (Géraudie and Meunier, 1984; Géraudie, 1984). Actinotrichia appear also in the temporary ventral finfold of the teleost embryo, for examples as in the trout embryo (Géraudie, in preparation), and then they dissapear when this structure vanishes during later development. On the contrary, in Chondrichthyes, their supposed homologous elements, the ceratotrichia extend largely on both dorsal and ventral sides of the paired and median fins (Kemp, 1977). So far, on the basis of morphology and fine structure, actinotrichia are considered to be homologues of ceratotrichia found in Chondrichthyes, where elastoidin has been biochemically and biophysically analyzed (Woodhead-Galloway and coll., 1977, 1978; Chandross, 1982; and in the present book).