Scolex and proglottids are characteristic of
Tapeworms within class Cestoda exhibit highly specialized body plan for intestinal endoparasitism in vertebrate hosts. Scolex serves as holdfast organ bearing four muscular suckers and, in Cyclophyllidea, retractable rostellum with hooks anchoring firmly to host mucosa resisting peristalsis. Immediately behind lies proliferative neck generating strobila composed of serial proglottids, each containing complete set of hermaphroditic reproductive organs maturing anteroposteriorly becoming gravid containing eggs. Nutrient absorption occurs across syncytial tegument due to absent alimentary canal.
Ref: Campbell Biology, 12th ed., Chapter 33: Cestoda scolex proglottids parasitic adaptations