Question

though cephalochorates do not possess heart , how can they have closed circulatory system?

Answer 1

ephalochordates have a closed circulatory system (the blood is enclosed in blood vessels) but lack a central pump (heart). Instead, the blood is propelled by pulsation (rhythmic contraction and relaxation) of several blood vessels. The blood contains no pigments or cells and is thought to function largely in nutrient distribution rather than in gas exchange and transport. The central nervous system of the cephalochordates is very simple. A dorsal nerve cord extends through the length of the body, giving rise to segmentally arranged nerves. No brain is detectable. The skin is rich in sensory nerve endings that probably help produce a sense of touch and are important for burrowing. A number of cephalochordates have some photosensors near the front and back ends of their body, but in general (unlike vertebrates) they lack any eyes or organs to sense gravity.