OBSERVATIONS ON THE MORPHOLOGY OF TRUTTAEDACNITIS-CLITELLARIUS AND TRUTTAEDACNITIS-LEBEDEVI (NEMATODA, CUCULLANIDAE) FROM ACIPENSERIDS AND SYNONYMY OF THE 2 SPECIES

Truttaedacnitis clitellarius (Ward & Magath, 1917) (Nematoda: Cucullan idae) is redescribed from the lake sturgeon Acipenser fulvescens from North America and compared with T. lebedevi (Skrjabina, 1966) from the Siberian sturgeon A. baeri. Studies on the morphology and morphometri cs of the two species reveal considerable overlap with unique shared c haracters, such as the previously unreported position of the excretory pore at the level of the pseudobuccal capsule and arrangement of caud al papillae. This position of the excretory pore is anteriormost among all cucullanids. Although there is a trend towards smaller size of bo dy and spicules in T. lebedevi, this reflects a long period of geograp hical separation and likely accounts for the minor morphological varia tions noted. Consequently, the two species are synonymised. The presen ce of one species of Truttaedacnitis, T. clitellarius, specific to fre shwater acipenserids in North America and Siberia, suggests an ancient origin and slow rare of evolution for this cucullanid.