These small (<10 cm long) tapeworms are best known for the spiny tentacles which adorn their scolices. They may be pathogenic in their intermediate hosts.
These are parasites of the stomach and spiral valve of elasmobranchs. Few life cycles are known in their entirety, but plerocercoid stages are present in many marine fish, crustaceans and molluscs, suggesting that they are second intermediate hosts, and that first intermediate hosts harboring a procercoid must be present as well.
The scolex bears four retractable tentacles, covered with spines. There are also two bothridia. Mature proglottids have testes located anterior and posterior to the ovary, and the female genital pore opens posterior to tha male genital pore. The mature proglottid can resemble those of several other taxa, so a scolex is necessary for reliable identification. Because of the importance of the scolex, there is an extensive nomenclature developed to describe its unique components.