It inhabits tide pools and surge channels and has been found living inside such invertebrates as salps.

Mendosoma lineatum was first formally described in 1848 by the French zoologist Alphonse Guichenot with the type locality given as Valparaiso Bay in Chile.

[5] There are rows of brown spots creating thin stripes along the flanks, becoming more reticulated in pattern on the back.

[7] Mendosoma lineatum is found in the subantarctic and temperate waters of the Southern Ocean around New Zealand, Chile and Tasmania, as well as Gough Island in the South Atlantic, and Île Saint-Paul and Amsterdam Island in the southern Indian Ocean.

[1] It has been recorded as prey for Northern rockhopper penguins (Eudyptes (chrysocome) moseleyi) and snoek (Thyrsites atun).