Answer: 1. Protostome development./2. Bilateral symmetry/4. Three embryonic germ layers
Explanation:
Over 600 million years ago some animals invaded aquatic and terrestrial environments in the pre-Cambrian period. These animals were enforced by huge evolutionary irradiation, and now they occupy every environment on planet Earth. From tiny insects and crustaceans smaller than 1mm in length to giant crabs from Japan that can reach 3m (with open legs), the arthropods are found in all size models, with an estimated number of more than one million species described. Concerning characteristics they are - Bilateral, triploblastic( Three embryonic germ layers), prostomial. Internally and externally segmented body, divided into at least two regions, head, and abdomen; typically with a cephalic shield or carapace. Opened circulatory system; the dorsal heart is a muscle pump with lateral Ostia for blood return.
