A. Choudhury et Ta. Dick, OBSERVATIONS ON THE MORPHOLOGY, SYSTEMATICS, AND BIOGEOGRAPHY OF THE GENUS TRUTTAEDACNITIS (NEMATODA, CUCULLANIDAE), The Journal of parasitology, 82(6), 1996, pp. 977-987
All species of Truttaedacnitis Fetter, 1974, were examined for a phylo
genetic analysis. Morphological studies showed that Truttaedacnitis tr
uttae (Fabricius, 1794) from North America possessed a reduced button-
shaped or nipple-shaped caudal mucron that is in contrast to the sharp
spike-shaped mucron commonly reported in Eurasian specimens. Histolog
ical studies showed that the excretory pore in Truttaedacnitis sphaero
cephala (Rudolphi, 1809) was situated near the level of the pseudobucc
al capsule between the 2 parts of the ventral cephalic ridge. Cucullan
us heterodonii Johnston and Mawson, 1943 is transferred to Truttaedacn
itis based on the presence of prominent cephalic plates separated by s
utures. An hypothesis regarding interrelationships among Truttaedacnit
is spp. was developed using phylogenetic systematics. The anterior exc
retory pore is a synapomorphy supporting the monophyly of Truttaedacni
tis clitellarius (Ward and Magath, 1917) and T. sphaerocephala parasit
izing sturgeons. The arrangement of cephalic plates indicates that Tru
ttaedacnitis pybusae Anderson, 1992 and T. truttae may form a monophyl
etic group and further supports the monophyly of T. clitellarius and T
. sphaerocephala. Using unordered character states of different cephal
ic plates produced a cladogram that suggested that species in holarcti
c/circumboreal families (Acipenseridae, Salmonidae, Petromyzontidae) m
ay be monophyletic. The systematics and biogeography of the various sp
ecies of Truttaedacnitis and their host specificity indicate that asso
ciations in this parasite genus are very ancient and of a relictual na
ture, determined largely by past continental and oceanic configuration
s, and a combination of vicariance and dispersal.