Xenacanthus is a relatively small member of its
order.
X. decheni reached about ,
X. meisenheimensis reached up to ,
X. (
Expleuracanthus)
gaudryi reached .
X. parallelus is one of the smallest xenacanths, males reached and females reached , both are fully grown. The
dorsal fin was ribbonlike and ran the entire length of the back and round the tail, where it joined with the
anal fin. This arrangement resembles that of modern
conger eels, and
Xenacanthus probably swam in a similar manner. A distinctive spine projected from the back of the head and gave the genus its name. The spike has even been speculated to have been venomous, perhaps in a similar manner to a sting ray. The teeth had an unusual "V" shape, and it probably fed on small
crustaceans and heavily scaled
palaeoniscid fishes. As with many xencanths,
Xenacanthus is mainly known because of fossilised teeth and spines. Fossils are known from the
Carboniferous-
Permian of North America, Europe, and South America.
Triassic species have been moved into the separate genus
Mooreodontus. == Species ==