MACROEVOLUTIONARY PATTERNS OF MORPHOLOGICAL DIVERSIFICATION AMONG PARASITIC FLATWORMS (PLATYHELMINTHES, CERCOMERIA)

Patterns of parasite morphological diversification were investigated u sing a morphological data base for the parasitic platyhelminths compri sing 1,459 characters analyzed using phylogenetic systematic methods. Only 10.8% of the 1,882 character transformations are losses, casting doubt on views that parasites are secondarily simplified and exhibit d egenerate evolution. Chi-squared analysis indicates that character los s in the Digenea and Monogenea occurs in proportion to total change an d is disproportionately lower within the Eucestoda. In the Digenea few er female characters and more male characters have been lost than expe cted by the total number of characters in that group, and more male an d more nonreproductive characters have been lost in proportion to thei r distribution across groups. In the Monogenea fewer nonreproductive a nd more larval characters have been lost than expected within the grou p, and female character loss is high relative to other groups. In the Eucestoda fewer female and more larval characters have been lost than expected within the group, whereas loss of male and nonreproductive ch aracter is low, and loss of larval characters is high, compared to the other groups. Patterns of character loss result partially from charac ters that show repeated (homoplasious) loss in different groups. High consistency index and low homoplasy slope ratio values indicate that t he parasitic platyhelminths show unusually low levels of homoplasy. ca sting doubt on views that parasite morphology is unusually adaptively plastic. Homoplasy within the monogeneans occurs in proportion to over all character change, is slightly higher than expected in the digenean s, and is much lower than expected within the eucestodes. Homoplasy oc curs less often than expected in larval characters, and more often tha n expected in nonreproductive characters in the Digenea. Monogeneans s how more homoplasy than expected for larval characters both within and among groups. Eucestodes show fewer homoplasious male and nonreproduc tive, and more homoplasious larval, characters than expected within th e group, and higher homoplasy in larval characters and lower homoplasy in female and nonreproductive characters among groups.