BI256 Lecture Notes - Lecture 9: Digenea, Monogenea, Trematode Life Cycle Stages
Document Summary
Covered by syncytial tegument (vs. cuticle of nematodes) Traditionally placed in the class trematode but now forms its own class. Complex life cycle with at least 2 hosts first usual a mollusc and the definitive (last) being a vertebrate) Excretory system contains ciliated cells (flame cells = protonephridia) extending into excretory tubes. Nervous system present although difficult to visualize. Reproduction most species are hermaphroditic: larvae can reproduce asexually (polyembrony, exception: schistosomes; adult worms reproduce sexually. Life cycle typically includes 2 or more intermediate hosts. Species specificity for 1st intermediate host always high. Specificity for other intermediate, and definitive hosts low. Adulthood only achieved in a definitive vertebrate host. Life cycle includes asexual replication of developmental stages, normally in 1st intermediate host. Adults usually parasites of vertebrate animals. Parasitic forms enter their hosts via the digestive system or by penetration of the skin. Found in veins, intestine and urinary bladder (spp. Causative agents of schistosomiasis: humans over 200 million people infests.
