I have had a hard time distinguishing this species from the similar H. leucospilota, which reportedly tends to be more slender and with longer and more conspicuous oral tentacles. The way I have them divided up, H. atra are not especially long and covered with sand (although often leaving bare patches where the black shows through), and usually lives out in the open from the intertidal to moderately shallow subtidal areas. Intertidal ones are often clustered in large numbers while those subtidally are often single or in small groups. H. leucospilota is often seen stretched out of holes in the reef, particularly in intertidal "tidepools" where reef rock has been quarried for construction purposes. However, that may not be a valid distinction, and it is possible that some of those on this page are in fact the latter species.
The photo below shows bare patches in the sand coat often seen in H. atra.
Typical clusters in intertidal pools.
The white spotting on black make this Asterophilia sp. commensal worm hard to see on the sand specked black Holothuria atra.
Created 22 June 2018
Updated 12 February 2024