4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是体的，生殖系统适于体内受精。单起源的吸虫（单殖纲）大多是鱼的外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是雌雄同体，生殖系统适于体内受精。单起虫（单殖纲）大多是鱼外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是雌雄同的，生殖系统适于精。单起源的吸虫（单殖纲）大多是鱼的外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫雌雄同体的，生殖系统适于体内受精。单起源的吸虫（单殖纲）鱼的外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

是雌雄同体，生殖系统适于体内受精。单起源吸（单殖纲）大多是鱼外寄生。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是雌雄同体的，生殖系统适于体内。起源的吸虫（殖纲）大多是鱼的外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是雄的，生殖系统适于内受精。单起源的吸虫（单殖纲）大多是鱼的外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是体的，生殖系统适于体内受精。单起源的吸虫（单殖纲）大多是鱼的外寄生虫。

4 Turbellarians are monoecious with the reproductive systems adapted for internal fertilization. And the monogenetic flukes (class Monogenea) are mostly ectoparasites of fishes.

涡虫是雌雄同体，系统适于体内受精。单起源吸虫（单纲）大多是鱼外寄虫。