Tumidotheres maculatus has a wide range in the western Atlantic Ocean, extending from the seas of Martha's Vineyard (United States) to San Matías Gulf (Argentina).

[3] Tumidotheres maculatus is an endosymbiont of molluscs; it is unclear whether the host is harmed by the crabs presence, that is whether the relationship is commensal or parasitic.

They include Argopecten irradians, Atrina rigida, Modiolus americanus, Mytilus edulis[3] and Flexopecten felipponei.

[4] It has also been found in a tunicate of the genus Molgula, in the tubes of the tubeworm Chaetopterus variopedatus and on the asteroid (starfish) Asterias rubens.

[3] Reported rates of infestation of T. maculatus on mollusc hosts vary widely, from 0%–20% on Argopecten irradians at St. Joseph Bay, Florida, to 97.6% on Mytilus edulis at Quicks Hole, Massachusetts.