Worm

On Sagan IV, the word worm is used to describe the mostly vermiforme members of the phylum Sagavermes of the kingdom Binucleozoa. They originated from a tiny, green, worm-like creature, but then they diverged into many shapes and sizes.

Anatomy
Many worms have a vermiforme body, but some have given up this morphology and turned to piscine, and even insect-like forms. One line even evolved an endoskeleton and evolve to be vertebrate-like creatures (in the case of saucebacks).

Breathing and Blood
Worms mainly breathe by diffusing oxygen into their skin. Creatures like the saucebacks breathe through microlungs on the flank of their tails. Since their blood carries oxygen and contains hemoglobin (which contains iron), it is red.

Evolution
One line of worms descended from the twelve-winged worm used their wings as light-collectors, and then they evolved to be photosynthetic. Then they evolve to be completely sedetary, not able to move at all. They then evolved into strange new forms, the treeworms. Their sexual fluids adapt to a nectar-like substance, and they depend on the xenobee (another type of worm) for pollination.

Senses
No coherrent sense organs evolved in the very first worm, so they have variable senses, variably configured. One line of worms descended from the pollenivorous silkworm have the eyes run along the back, while another line descended from the stumpworm evolved them to be in front. Saucebacks, another line descended from the stumpworm, don't have eyes at all, they use echolocation to sense the world around them. Saucebacks also have many moist olfactory patches around the mouth, which gives them a strong sense of smell. Another group of the Sagavermes who has an excellent sense of smell would be the bubblehorns. The beakworms eyes are vertebrate-like. At first, it was just a single eye with two retinas, but then in some forms they have split into two functional eyes.