Platyhelminthes

• PLATYHELMINTHES from Latin, platy - ‘flat’ + Greek helminth ‘worm’.
• Usually flattened dorsoventrally, triploblastic, acoelomate

  • Unsegmented worms, bilaterally symmetrical; Somewhat cephalized; Epidermis may be cellular or syncytial (ciliated in some); rhabdites (secrete mucus)

  • Sense organs include statocysts (organs of balance) and ocelli.
• Phylum Platyhelminthes Flatworms ; bilateral acoelomates . More than 34,000 species
• Class Turbellaria

  Mostly free living and aquatic; external surface usually ciliated ; predaceous; possess rhabdites, protrusible proboscis, frontal glands, and many mucous glands; mostly hermaphroditic. Convoluta, Notoplana, Dugesia. More than 3,000 species.
• Class Monogenea

  Monogenetic flukes ; mostly ectoparasites on vertebrates (usually on fishes; occasionally on turtles, frogs, copepods, squids); one life-cycle form in only one host; bear opisthaptor. Disocotyle, Gyrodactylus, Polystoma. About 1,100 species.
• Class Trematoda

  Trematodes ; all are parasitic; several holdfast devices present ; have complicated life cycles sexual and asexual reproduction. More than 10,000 species.
• Subclass Aspidogastrea

  Mostly endoparasites of molluscs; possess large opisthaptor; most lack an oral sucker Cotylaspis, Multicotyl. About 32 species.
• Subclass Digenea

  Adults endoparasites have oral sucker in vertebrates; at least two different life-cycle forms in two or more hosts; and acetabulum. Schistosoma, Fasciola, Clonorchis. About 1,350 species.
• Class Cestoidea

  All parasitic with no digestive tract ; have great reproductive potential species. tapeworms. About 3,500
• Subclass Cestodaria

  Body not subdivided into ; tapeworms. About 3,500 proglottids; larva in crustaceans, adult in fishes About 15 species. Amphilina, Gyrocotyle.
• Subclass Eucestoda

  True tapeworms; body divided into . Amphilina, Gyrocotyle. scolex, neck, and strobila; strobila composed of many proglottids ; both male and female reproductive systems in each proglottid; of vertebrates adults in digestive tract . Proteocephalus, Taenia, Echinococcus, Taeniarhynchus; Diphyllobothrium. About 1,000 species
• PLATYHELMINTHES

  • Incomplete gut. Food digestion is extracellular.

  • Protonephridia networks of fine tubules that run the length of the organism, along each of its sides.

  • Flame cells removing waste materials through filtration
• PLATYHELMINTHES

  • Commissures points of union connect the nerve cords.

  • Auricle sensory lobes may project from the side of the head, (chemoreceptors) that aid in food location.

  • Monoecious with internal fertilization. Reproduce asexually by transverse fission.

  • The two (or more) animals that result from fission are called zooids