After some digging, it's a synonym - i'd support merging it under Cercodemas anceps

The version "Pentacta anceps" seemed an old import from EoL, and nothing there for it now - i was very skeptical about it being in the scientific literature!
(it seemed like i know for other traded invertebrates where scientific sounding names get made up or altered for trade only - here either aquariums or food)

Cercodemas anceps Selenka, 1867 original is here
https://www.biodiversitylibrary.org/page/45007590#page/373/mode/1up

This was the lead in -
https://www.academia.edu/10337293/Sea_cucumber_species_of_the_Merambong_Shoal_with_notes_on_the_distribution_and_habitat_of_the_dominant_species
it's a pdf on there, Woo et al. 2014 "Sea cucumber species of the Merambong Shoal" (etc) Malayan Nature Journal 2014, 66(1 and 2), 139-145

For new malaysian specimens that reads:
Cercodemas anceps Selenka, 1867
Cercodemas anceps Selenka, 1867; Rowe and Gates, 1995; Puchakarn and Sonchaeng, 2004: 426; Marsh and Morrison, 2004: 329;
Pentacta anceps Clark and Rowe, 1971: 180; Maxwell and Cresswell, 1981; Huang et al., 2006
Materials examined: Two specimens collected from the seagrass bed of Merambong Shoal (Johor, Malaysia), exposed seagrass bed (low spring tide).
Description: Short and ... [etc]

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So yah, seems
Cercodemas anceps Selenka, 1867 = Pentacta anceps (Selenka, 1867)
and we have it misduplicated.

The citation "Clark and Rowe, 1971" goes to "Clark, A.M. and Rowe, F.W.E. 1971. Monograph of the shallow-water Indo-West Pacific Echinoderms. London: Trustees of the British Museum (Natural History), pp 171-209." which doesn't appear to be on my bookshelf! Yet - thanks to whatever powers - the pdf is online here http://www.abctaxa.be/downloads/additional-information-volume-1/works-famous-holothuroid-workers/fwe-rowe/MonographIndoWestPacific.pdf
On p. 180 its indeed used in a table as revised Petacta anceps (Selenka, 1867), then slightly explained in footnote 14 on p.194/195. - whether that proposal is technically valid at that time etc is beyond my current willpower to deduce, but it was proposed.

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The essence is that seems some subsequently followed the proposal to transfer to Pentacta, others didn't - the aquarium community at least for an age seemed to have been using that revised "Pentacta anceps:"

I'd say it's worth a consult to WORMS as some mention of the revised combination Petacta anceps (Selenka, 1867) seems like would be good to have under Cercodemas, but usage seems to shifted back to original Cercodemas anceps Selenka, 1867 for whatever reason!

p.s.
Looking forward to the day someone ever pays me to make the absurdity of variant taxonomic schemes consistent across at least the main framework resources!