Sentence:  The scolex exhibits a retractable <WSD>rostellum</WSD> with crowns of recurved thorn-like hooks and four cup-like suckers. 
Meaning of the word marked with <WSD> tags:  A retractable protruding part at the anterior end of a soft-bodied tapeworm; the scolex from which it protrudes is often armed with hooks which serve to keep it in place attached to the host.