There are several characteristic morphologic features shown in these nice images from Florida Fan. First, we have a long segment of a relatively large tapeworm, with proglottids that are wider than they are long. Immature proglottids of Taenia solium and T. saginata can also be wider than they are long, but the fact that we could get eggs from the proglottids means that they are mature. Therefore, we can exclude Taenia based on the shape of the proglottids. We can also exclude the other human tapeworms since none are this large.
Another feature that I find to be helpful for identifying Diphyllobothrium is that the uterine structures are clearly visible in the center of each proglottid - even without staining or microscopic examination:
Finally, the eggs that were found in the accompanying fluid leave no doubt as to the identification, having the classic shape and features of Diphyllobothrium, including an operculum and abopercular knob.
As Anon pointed out, species identification would require epidemiological information, and ultimately molecular testing. Therefore, we report this out as "Diphyllobothrium species" in my lab.
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