The flatworm is a member of the “flatworm” group as opposed to “round worms” (nematodes) and “segmented worms” (earthworms). It also is commonly called a “terrestrial flatworm.” Although, not common in the Central Coast landscape, it is also not rare. I find about a half dozen per year on the sidewalks/driveways in my neighborhood in the Orcutt area. There are several genera and many species of flatworms. Most are aquatic, living on rocks in streams and pools.
The flatworm is anywhere from three to seven inches long, very flat (a cross section of the body has the shape of a lens), the color is a dark grayish brown and the head flat and half-moon shaped.
The terrestrial flatworm or land planarian can survive out of the water, but must have a very moist environment. The ones I see usually have managed to crawl onto the sidewalk out of the lawn on nights when fog and dew wet the concrete. If the worm cannot find its way back into the turf very soon after sunrise, death due to dessication is very quick.
Flatworms are covered with a very sticky layer of mucus – it is almost like glue. The worm lays down a mucus trail wherever it goes. The mucus helps smooth out rough (abrasive) places and also helps in the locomotion of the worm.
Flatworms have an interesting digestive process. When they find something to eat, they attach themselves to it and then regurgitate digestive fluids onto the food. Digestion then occurs outside the body, and the animal ingests (sucks in) whatever has been digested (liquefied). Food consists of bits of protein and other debris the worm finds on or near the soil surface. Undigestible food particles are ejected back out through the mouth, since flatworms have no anus.
Flatworms also have great powers of regeneration. If you cut one in half, the head-end will develop a new tail, and the tail-end will develop a new head.
To my knowledge, flatworms cause no harm and are beneficial in that they help recycle plant and animal debris. They are a curiosity and are part of the biodiversity that is present on the Central Coast.