in the protostome line the blastopore becomes the

The endoderm gives rise to the lining of the digestive tract (including the stomach, intestines, liver, and pancreas), as well as to the lining of the trachea, bronchi, and lungs of the respiratory tract, along with a few other structures. The mesoderm gives rise to the central nervous system.Įach of the three germ layers is programmed to give rise to particular body tissues and organs.The endoderm gives rise to the lining of the digestive tract and the respiratory tract.Animals that display bilateral symmetry are triploblasts.Animals that display radial symmetry are diploblasts.Which of the following statements about diploblasts and triploblasts is false? They are believed to have evolved from bilaterally symmetrical animals thus, they are classified as bilaterally symmetrical. This is termed secondary radial symmetry. In evolutionary terms, this simple form of symmetry promoted active mobility and increased sophistication of resource-seeking and predator-prey relationships.Īnimals in the phylum Echinodermata (such as sea stars, sand dollars, and sea urchins) display radial symmetry as adults, but their larval stages exhibit bilateral symmetry. In contrast to radial symmetry, which is best suited for stationary or limited-motion lifestyles, bilateral symmetry allows for streamlined and directional motion. The evolution of bilateral symmetry that allowed for the formation of anterior and posterior (head and tail) ends promoted a phenomenon called cephalization, which refers to the collection of an organized nervous system at the animal’s anterior end. All true animals except those with radial symmetry are bilaterally symmetrical. Animals with bilateral symmetry have a “head” and “tail” (anterior vs. Radial symmetry equips these sea creatures (which may be sedentary or only capable of slow movement or floating) to experience the environment equally from all directions.īilateral symmetry involves the division of the animal through a sagittal plane, resulting in two mirror image, right and left halves, such as those of a butterfly ( d), crab, or human body. This form of symmetry marks the body plans of animals in the phyla Ctenophora and Cnidaria, including jellyfish and adult sea anemones ( bc). The two halves of a radially symmetrical animal may be described as the side with a mouth or “oral side,” and the side without a mouth (the “aboral side”). It results in animals having top and bottom surfaces but no left and right sides, or front or back.

Radial symmetry is the arrangement of body parts around a central axis, as is seen in a drinking glass or pie. All types of symmetry are well suited to meet the unique demands of a particular animal’s lifestyle. Only a few animal groups display radial symmetry. Asymmetry is a unique feature of Parazoa ( a). Arthropods are more closely related to nematodes than they are to annelids.Īnimal Characterization Based on Body SymmetryĪt a very basic level of classification, true animals can be largely divided into three groups based on the type of symmetry of their body plan: radially symmetrical, bilaterally symmetrical, and asymmetrical.Acoela and Cnidaria both possess radial symmetry.Lophotrochozoa and Ecdysozoa are both Bilataria.Eumetazoans have specialized tissues and parazoans don’t.Which of the following statements is false?

In the protostome line the blastopore becomes the