. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MOLECULAR PHYLOGENY OF DICYEMIDS 89 • \eni>pus laevis — Artemia salina — Asterta* amurenxix j~ Crasso ITI= i PI • Sagitta crassa Crassostrea gigux Shistosoma mansoni Dugesia japonica • Planncera mullitentaculata 'Molini/nrmix molimformis —^—^^— Caenorhabditis elegans l^""""/"'" naika ^_____^_^_^— Henneguya sp. • Dicvema acuticephalum "I— Dic\ema oriental? Triploblasts. .\nemonia xulcata Trichoplax adhaerens Beroe cucumis Scvpha ciliata Arabidapsis thaliana Vnlvox carteri Hartmanella verm
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MOLECULAR PHYLOGENY OF DICYEMIDS 89 • \eni>pus laevis — Artemia salina — Asterta* amurenxix j~ Crasso ITI= i PI • Sagitta crassa Crassostrea gigux Shistosoma mansoni Dugesia japonica • Planncera mullitentaculata 'Molini/nrmix molimformis —^—^^— Caenorhabditis elegans l^""""/"'" naika ^_____^_^_^— Henneguya sp. • Dicvema acuticephalum "I— Dic\ema oriental? Triploblasts. .\nemonia xulcata Trichoplax adhaerens Beroe cucumis Scvpha ciliata Arabidapsis thaliana Vnlvox carteri Hartmanella vermiformis Oxytriclia nova Paramecium tetraurelia ^—^— Crypthecodinium cohmi Diploblasts I Plants Protists Sacrcocystis murix ' Theilena annulala • Saccharomyces cerevisiae Firobasidiella neoformans Fungi Figure -4. Maximum-likelihood tree showing the phylogenetic position of the dicyemids among 28 rep- resentative eukaryotic groups. The tree was obtained using the fastDNAML algorithm with a transition/ transversion ratio of which gave the best maximum-likelihood score (In likelihood = - ). Branch lengths are proportional to the scale given in substitutions per sequence position. Because of the long computation time (more than 12 h per replication), bootstrapping was not performed. degeneratively simple animals descended from a more complex triploblastic ancestor. Recent close observations of dicyemid development (Furuya t'/fl/., 1992b. 1994) do not contradict the present inference; spiral cleavage, a de- terminative mode of cell division, and the formation of stereoblastula-like structure through epiboly. as seen in the development of vermiform and infusoriform embryos, are reminiscent of flatworms. Myxozoans are also re- garded as an extreme example of the degeneration char- acteristic of parasitic evolution (Smother el a/.. 1994). At present we can say little about the ancestor from which the dicyemids were derived. Molecular an
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
