Complex sentence: Starfish and other echinoderms pump water directly into their bodies through their water vascular system and this makes them vulnerable to water pollution as they have little ability to filter out the toxins and contaminants.
Split into simpler sentences: Starfish and other echinoderms pump water directly into their bodies through their water vascular system. This makes them vulnerable to water pollution, as they have little ability to filter out toxins and contaminants.