1. All animals have body plans that are modifications from an original ancient ancestral animal body plan. This is proven with the similarities between different animals. The rat, dogfish shark, crayfish, pigeon and squid all have both a central nervous system and peripheral nervous system. This shows that they all are interrelated. Also, their respiratory systems are all similar. All the listed animals need oxygen, they just get it in different ways. The rat and pigeon take in oxygen while the dogfish shark, crayfish and squid all use gills to receive oxygen.
2. The evolutionary development of body plans ranges from the simplest to the most complex. Some animals that are complex are the rat and pigeon. The rat has bones similar to the human. The pigeon also has bones, but they are lightweight which allows them to fly with ease. The squid is an example of an animal with simple body plans. They do not live long and have no bones. Their skeletal system has very little structure. I believe that if the chordate is the most complex phylum, the most simple is the mellesca. The order I would put them in from simplest to most complex would be: squid, crayfish, dogfish shark, rat and pigeon.
3. a. The special adaptations of the rat are its ability to keep itself cool with its tail
and scavenge for food.
b. The rat eats food with its mouth. The process of breaking down its food starts in the
salivary glands. It continues through the esophagus and into the stomach where the food
gets broken down.
c. An incomplete digestive system is where a single opening serves as the mouth and anus of
the organism. A complete digestive system is where there are two openings, a mouth and
anus. Rats have complete digestive systems.
d. Rats breathe in oxygen and breathe out carbon dioxide.
e. Rats have closed circulatory systems. A closed circulatory system is one where the blood
stays closed inside veins and tubes. An open circula...