Pseudaxine trachuri is a species of monogenean, parasitic on the gills of a marine fish.

The haptor is oblique and unilateral, and bears numerous clamps arranged in a single row.

In fact, the asymmetry of P. trachuri fulfills an important function, which is to bring the longitudinal axis of the body parallel to the gill-ventilating current.

Llewellyn studied the adhesive attitude of P. trachuri and revealed that it attaches near to the distal ends of primary lamellae.

In P. trachuri, the longitudinal axis of the body is inclined to the adhesive organs at an angle that varies between 30 and 50°.

Sometimes, it bends through 180° so the body of P. trachuri comes in contact with the opposite side of the same lamellae to which its haptor is attached.

During the summer months of July, August and September, only adult specimens of Pseudaxine trachuri are found on the gills of their hosts.

This cessation of reproductive activity ‘anticipates’ a change in host behaviour, as young scads leave the bottom, where infection occurs, in July and become plankton feeders and thus migrate to look for pelagic-food-organisms.

its alimentary canal consists only of a mouth, pharynx, and a simple sacculate intestine.

The alimentary canal of these larvae are provided with two buccal suckers, an intestine differentiated into an oesophagus that bifurcates into two branches.

The walls of the oesophagus and the intestine are lined by pigment cells, resembling those found in adult Polyopisthocotylea, suggesting that the larvae also feed on blood.