Complex sentence: Although euglenids share several common characteristics with animals, which is why they were originally classified as so, there is no evidence of euglenids ever using sexual reproduction, which is just one of the reasons why they could no longer be classified as animals.
Split into simpler sentences: Although euglenids share several common characteristics with animals, which is why they were originally classified as so, there is no evidence of euglenids ever using sexual reproduction. This is one of the reasons they could no longer be classified as animals.