Phylum Platyhelminthes
Bilateral symmetry. Triploblastic with parenchymatous tissue layer. Blind ended gut. Dorsoventrally flattened. No circulatory system. Cephalization. Protonephridia. Nervous system arranged in longitudinal fibers. Generally hermaphroditic. Spiral cleavage.

Class Turbellaria
Free living, primarily aquatic, some terrestrial. Ciliated epidermis provides locomotion on secreted mucus. Undulating locomotion in large aquatic forms and all terrestrial forms. Prominent gland cells in epidermis. Rhabdoids and rhabdites in epidermis. Neoblasts facilitate regeneration. Pigment cup eyes and ciliated chemosensory pits. Gut varies from a syncitial mass (acoels), to a simple sac (rhabdocoels) to a complex of lateral diverticulae (triclads and polyclads). Archoophoran or neoophoran. Asexual reproduction by transverse fission.
Kaburakia excelsa - marine turbellarian
Geoplana sp. - terrestrial planarian
Planaria sp. - freshwater planarian [1] [2]
Bdelloura sp. - triclad commensal on book gills of Limulus sp.

Class Trematoda
Endoparasitic, all life cycles involving a molluscan host. Oral sucker and acetabulum for attachment. All neoophoran.

Subclass Aspidogastrea
Acetabulum elaborate with many septa and alveoli. Parasites of molluscs that can infect molluscivorous vertebrates opportunistically.
aspidobothrian

Subclass Digenea
The flukes. Adults parasitic in vertebrates with a molluscan intermediate host (complex life cycle). Simple acetabulum for attachment.
miracidium
sporocyst
rediae [1] [2]
cercaria
metacercaria
Fasciola hepatica - sheep liver fluke [1] [2] [3]
Fasciolopsis buski - human intestinal fluke [1] [2]
Prosthogonimus macrorchis - oviduct of domestic fowl
Clonorchis sinensis - chinese liver fluke [1] [2]

Class Monogenea
Monopisthocotyleans generally ectoparasitic on fish, polyopisthocotyleans often endoparasitic in bladder of amphibians. Onchomiracidium larva with cercomer. Prohaptor with adhesive glands, opisthaptor with hooks (Monopistocotylea) and/or suckers (Polyopisthocotylea).
Cleidodiscus sp. - monopishtocotylean gill parasite of freshwater fishes
Urocleidus adspectus - monopisthocotylean gill parasite of yellow perch (Perca flavescens)
Tetraonchus monenteron - monopisthocotylean gill parasite of northern pike (Esox lucius)
more monopisthocotyleans [1] [2] [3]
polyopistocotyleans [1] [2] [3]

Class Cestoidea
No digestive tract. Digestion by absorption across tegument folded into microtriches. Body consisting of scolex, neck (germinative region), and proglottids. Scolex with hooks, acetabula, or bothria for attachment.
Order Cyclophyllidea
Scolex with 4 acetabula, and might possess and armed or unarmed rostellum, Single compact vitellarium, no uterine pore.
Taenia sp. - whole worm
Taenia solium (pork tapeworm) - scolex
Taenia pisiformis - mature proglottid from canid
Echinococcus granulosus - adult from canid
Dipyllidium caninum - adult from dog
Monezia expansa - sheep tapeworm [adult] [scolex] [proglottid] [proglottid]
Order Pseudophyllidea
Scolex with bothria. Uterine pore present. Follicular, diffuse vitellaria.
Diphyllobothrium latum - broad fish tapeworm [scolex] [proglottid]

Phylum Nemertea (Rhynchocoela)
Vermiform, complete gut with terminal anus. Acoelomate, triploblastic. Dorsoventrally flattened. Some serially repeated organs. Eversible and retractable proboscis housed in a longitudinal dorsal cavity (rhynchocoel).
Amphiporus bimaculatus
enoplan nemertean
cross section through proboscis receptacle