The body of the sea tadpole is semitransparent,
with rose to whitish tinges and violet vertical fins. The pelvic sucker, formed
from modified pelvic fins, is slightly smaller than the eye, and is often used
as a diagnostic feature. Its body is elongate and roughly cylindrical from the
nose to the middle of the pectoral fin, where it tapers rapidly to the tail. This
is a small fish, rarely more than 8 cm in length. Its caudal and anal fins are
fused, making the sea tadpole look like it has a fin extending along its underside.
The sea tadpole has been found in the Gulf of St.
Lawrence, off Greenland, Norway and in the Kara Sea.