name two phyla of animals that are radially symmetrical
Symmetry in biology Symmetry has been important historically in the taxonomy of animals; Georges Cuvier classified animals with radial symmetry in the taxon Radiata (Zoophytes),[1][2] which is now generally accepted to be a polyphyletic assemblage of different phyla of the Animal kingdom.[3] Most radially symmetric animals are symmetrical about an axis extending from the center of the oral surface, which contains the mouth, to the center of the opposite, aboral, end. Radial symmetry is especially suitable for sessile animals such as the sea anemone, floating animals such as jellyfish, and slow moving organisms such as starfish. Animals in the phyla Cnidaria and Echinodermata are radially symmetric,[4] although many sea anemones and some corals have bilateral symmetry defined by a single structure, the siphonoglyph.[5]
Evolution of mammals The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the late Carboniferous period. The most ancestral forms in the class Mammalia are the egg-laying mammals in the subclass Prototheria. This class first started out as something close to the platypus and evolved to modern day mammals.[1] By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes.[2] Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.