The proboscis is the specialized attachment organ of acanthocephalans. It is a retractable sac covered with posteriorly-directed, curved hooks. The acanthocephalan retacts the proboscis using some internal muscles attached to its tip. As the proboscis retracts, it withdrawns within itself and the withdrawn hooks are now directed anteriorly. As the proboscis is everted, the process reverses. The anteriorly-directed hooks on the inside grip into host tissue and then turn posteriorly. This mechanism makes it easy for the acanthocephalan to insert and remove its proboscis, yet provides secure attachment.
The proboscis of Echinorhynchus is covered with over 100 medium-sized hooks.
