It is found in saltwater sea floor habitats off the coast of Europe, predominantly Sweden.

[1] The unusual digestive structure of this species, in which a single opening is used to eat food and excrete waste, has led to considerable study and controversy as to its classification.

It is a bottom-dwelling, burrowing carnivore that eats mollusks (likely larval forms, as opposed to hard-shelled adults).

Genus Xenoturbella is a member of sub-phylum Xenoturbellida, which are known as paradoxmaskar[2] – Swedish for "paradox worms" (a term that some popular media have applied to the species), because if it is classified as a deuterostome, it would be more closely related to humans than other, more complex, invertebrates such as lobsters.

In 1999, examination of X. bocki specimens held at the Swedish Museum of Natural History showed that a small subset of them must belong to another species.

The new taxon was named after Westblad, who collected the specimens from coarser and shallower habitats in the same range as X. bocki.

More recent studies suggest on the basis of genetic and developmental evidence (e.g. Hox genes) that it should be grouped with Acoela and Nemertodermatida into Acoelomorpha.

[11] A 2016 analysis of many genetic data sets supports the latter, and suggests that, like Xenoturbella bocki, the common ancestor of protostomes and deuterostomes likely had one opening, ciliated locomotion and a wormlike body.

An organ of unknown function, preliminarily called a statocyst, has been observed on the front end of the animal.

Experiments in which the animal was observed to cleave into two after a wound show that the statocyst is essential for normal behavior and long-term survival.

[9] Adults are known to have a symbiotic relationship with Chlamydiae and Gammaproteobacteria, two bacterial endosymbionts found in their gastrodermis.

At least one specimen that has been proposed to show a consumed bivalve larvae is preserved in the Swedish Natural History Museum.

This species burrows, and has been observed to make tunnels as deep as 15 cm (5.9 in) into substrate in a laboratory aquarium.