Annelides

Annelids Characteristics: The suspended digestive tube within the coelom of annelids is an important structural feature. This allows for the body and digestive muscles to work independently; making for better mobility and digestion! The segmentation of the body allows for subdivision of body functions by segments (for ex. sex organs are located in segments 10-35) and allows for easy growth (add on a few sections).

Marine worms - polycheate: These animals have blood for transporting carbon dioxide and oxygen (also moves food and wastes). They need blood because they are much larger that previous types of worms that used simple diffusion. Blood is carried by a closed circulatory system with major vessels running along the dorsal and ventral surfaces of the body. Hearts pump the blood to and from the segments of the body. The blood also has a pigment, hemoglobin, that greatly increases the oxygen carrying capacity of the blood. Gases move back and forth across the skin by diffusion (no lungs or gills).

Polycheate worms have a set of fangs then can shoot forward to capture prey (as found in the movie "Aliens"). Food is taken into a tube that runs the entire length of the body. The food is soil and is processed to remove useful organic molecules. It enters the mouth, then esophagus, crop, gizzard and lastly the intestine. Food molecules are taken up across the wall of the intestine and transported around the body by the circulatory system. Wastes are removed from each segment of the body by nephridia (nitrogenous wastes).

Movement in worms involves the coordinated contraction of circular muscles (makes the worm long and thin) and alternate contraction of longitudinal muscles (makes the worm short and fat). The parapodia of the worms can dig into the soil during circular contraction so the worm is pulled forward during the contraction of the longitudinal muscles. The marine worm is also a good swimmer but will only swim at night to avoid being eaten!