Which of the following is an unsegmented worm with a pseudocoelom.
a. sponge
b. cnidarian
c. arthropod
d. roundworm

The correct answer is option D, Round worm

Roundworm belongs to the phylum  Nematodes and some common characteristics of Nematodes are – they are small, slender , un-segmented, smooth and shiny. Roundworm has   a round body just like a spiny –headed worm which do not have segments . Also they possess a body cavity known as pseudocoel in which the internal body organs lie and the body cavity is not lined with mesodermal cells.  

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.