Complex sentence: The dorsal surface is smooth; there are five pairs of parapodia on the ventral surface, armed with supporting and hooked setae, by means of which the worm adheres to its host.
Split into simpler sentences: The dorsal surface is smooth, with five pairs of parapodia on the bottom surface. These parapodia are armed with supporting and hooked setae, by means of which the worm adheres to its host.