Land planarians, or land flatworms

Platyhelminthes are a very unusual phylum, loosely containing three classes, consisting of flukes, also known as trematodes, tapeworms, less known as cestodes, and flatworms, or planarians, all uncomfortably collected together at the moment into a subgroup known as Rhabditophora, even though planarians themselves are also confusingly known as platyhelminthes or platyhelminths too. It seems frankly very complicated, confusing and difficult to reach any consensus or definite conclusion about their interrelated status.
Anyway, interestingly for a website about soil mesofauna, some species of planarians have become fully terrestrial, free-living in damp soils, leaf litter and under logs. These land flatworms are also known as geoplanarians, gathered up and popped for practicality en mass into the family Geoplanidae.

They can be as small as 3mm, as large as 15-30mm. Some have the ability to entirely regenerate themselves to such an extent that, like the Sorcerer's Apprentice, only a small section of the body is needed as a template to begin regrowth. Not only that, some can be bisected lengthways or chopped in two midway and turn into two fully functioning animals. Losing a head isn't a problem. They just grow another one.

The pharynx, or eversible feeding tube is situated on the body's underside, halfway down. It also functions as an anus. Because of this they have to fully digest every meal and excrete before eating again.

Some terrestrial species have just two ocelli or eyes, like the snake-headed flatworm, R. sylvestris below, a native flatworm from the UK. Others can have an array of hundreds of light sensitive pigmented dots along their flanks.

Flatworms get their common name for when they are at rest, or disturbed. They dorsally flatten, thicken and contract their length as with the K. andersoni above. The animal below is the same one, stretched back to its full length, moving slowing across the substrate on its mucus slime.

They often have a taste for worms, like the infamous New Zealand flatworm, wreaking its tiny havoc across the gardens of the UK. They can also eat slugs, snails woodlice and insects.

Certain species of the Bipalium or hammerhead flatworms use the deadly neurotoxin, tetrodotoxin or TTX to immobilise their prey. This makes flatworms the only fully terrestrial animal so far discovered to use it. There is no antidote. Famously, it is the same compound present in Fugu, the Japanese puffer fish delicacy, which kills adventurous Japanese diners every year.