Lanarkia was an odd member of the thelodont group. Very close to the front, it had one thin pectoral fin on each side. On the caudal fin, it was basically just skin and bones. It had a very skinny v-shaped caudal fin.
Here are Lanarkia and some other thelodonts together. All thelodonts were jawless, so they had to suck in very tiny things into their mouths.
There are two species of the genus Lanarkia. They are Lanarkia spinosa and Lanarkia horrida.
Lanarkia lived in the Silurian Period and was a pretty small fish, so it had to avoid giant eurypterids, such as Pterygotus.