This study reports on the anatomy and structural details of the feeding apparatus and associated glands in a tropical fish ectoparasite, Argulus siamensis Wilson, 1926. The results reveal that anatomically the feeding apparatus of the species consists of a proximal buccal proboscis and a retractile pre-oral spine surrounded by a sheath. The mouth is located at the terminal end of the buccal proboscis. Two types of glands, the spinal gland and the proboscis gland, are associated with the feeding apparatus. The sac-like spinal gland, consisting of four polygonal cells, is located at the base of the spine. It is continuous with the median duct of the spine but does not show any connection with the buccal cavity. Numerous secretory vesicles are present in the cytoplasm. The proboscis glands are located parallel to the spinal sheath, one on both sides, and open directly into the buccal proboscis. Each proboscis gland houses two giant cells, the cytoplasm of which is largely occupied by secretory vesicles. The present study, aimed at understanding the functional relation of the glandular secretions with the feeding mechanism, revealed that the secretion of the spinal gland is neither cytotoxic nor haemorrhagic, but may have anaesthetic or vasodilatory activity. Indications are available to show that the secretion of the proboscis gland is anticoagulant in nature.