Question

Draw a simple phylogenetic tree of invertebrate phyla and discuss the meaning and importance of the following terms: radial vs. bilateral symmetry, diploblastic vs. triploblastic, and protostomes vs. deuterostomes.

Answer 1

Radial symmetry is the body plan having symmetrical arrangements of parts of the organism at any angle around a central axis such that the organism is divided into two equal halves by any plane passing through center of the body. Cnidarians and ctenophores possess radial symmetry.

Whereas in bilateral symmetry , organism can be divided into two equal halves which are mirror image of each other by only a single plane passing through the center and dividing the body into left and right halves. This arises from platyhelminthes.

Diploblastic : organism having two germ layers ( ectoderm and endoderm )

Triploblastic : organism having three germ layers ( ectoderm , mesoderm and endoderm)

Protostomes are the organisms in which blastopore develops into mouth whereas in deuterostomes , mouth forms secondarily from the gut ( gut forms posterior opening first which removes faecal matter ) .