Shell very small for the subgenus, with short spire, simple sutures, narrow whorls, fine sculpture, and a long, narrow anterior siphonal canal. Two varices present (including the terminal one) on adult shells; varices low but wide, with spiral cords very low where they cross the varices; varices slightly higher and wider over sutural ramp than lower down, and appressed against previous whorl (not separated from it by a groove, as in most similar species, including C. moniliferum). Spiral sculpture of 6 to 8 (7 on most specimens) low, narrow spiral cords on last whorl and 3 on spire whorls, raised around the shoulder angle into a row of low, rounded, and in some specimens weakly antero-posteriorly compressed nodules; spiral interspaces bear one median narrow secondary cord and 2 or 3 low, narrow, tertiary spiral threads. Collabral sculpture of low to moderately high folds, weak over sutural ramp and fading out gradually below the fifth main peripheral spiral cord on the last whorl, varying from low, narrow, closely spaced, and 6 or 7 in the last intervariceal space, to higher, more widely spaced, and as few as 3 in the last intervariceal space. Aperture small, elongate-oval, white to very pale flesh-pink, with a narrowly reflected outer lip bearing 8 narrow, prominent ridges on its inner edge. Inner Up narrowly reflected, with thick, smooth edge, bearing 3 prominent, narrow ridges on the parietal area and many on the basal columellar area, and many lower, less prominent ridges on the central columellar area. Teleoconch exterior uniform pale yellow-brown to pale orange-tan, except for slightly more darkly banded varices and a wide white to cream basal zone over the fourth and fifth spiral cords on the last whorl. Periostracum thin, pale straw-yellow, largely smooth apart from many low, thin, closely spaced collabral lamellae on the terminal varix. Protoconch (bearing its periostracum) pale olive-brown, of 4.5 whorls, smoothly conical, relatively laqje and broad (compared, for example, with those of specimens of C. pyrulum in the same samples). Dimensions. 48.4 x19.9 mm (holotype); 52.5 x 22.6 mm (largest paratype, BM(NH)1985114), 47.1 x 20.9 mm (paratype, BM(NH) 1953.1.12.162). Operculum small, widely fan-shaped with the nucleus at the centre of the columellar edge, bright red-brown.

Specimens dredged by R. Winckworth in Port Blair, Andaman Islands, belong in an unnamed species of Cymatium (Ranularia). This species was illustrated by Kilias (1973, fig. 103), on the basis of a specimen from the Andaman Islands, as C moniliferum moniliferum, but the new species clearly does not agree with A. Adams & Reeve's illustration (1850, pl. 10, fig. 18) of a syntype of Triton monilifer. Cymatium andamanense differs from C. moniliferum in its slightly smaller size (it rivals C exile (Reeve, 1844) as the smallest species in the subgenus), its lower, narrower, and more numerous spiral cords, its more steeply sloping shoulders without a subsutural cord or channel, its varices being particularly low except for their unusually high, "hunched" look over the shoulder, its more coarsely sculptured inner hp, its low, narrow apertural lips, the inner lip not raised into a collar as is always present in C. moniliferum its more numerous collabral folds on most specimens and hence more numerous, lower, and much less prominent nodules around the shoulder angle, its aperture being very pale flesh pink in some specimens, and in its much more consistently and uniformly yellow-brown to orange-tan exterior (not weakly but obviously marbled as in C. moniliferum). Unfortunately, a complete protoconch of C moniliferum has not been seen for comparison with C. andamanense. The new species differs from C. exile in its slightly wider and smoother apertural hps, its more prominent spiral cords, its lower and less angular nodules, and its much paler colour pattern lacking the bright red-brown splashes on the white background of C. exile.
The only other species that might be confused with Cymatium andamanense is a possible new species represented by four specimens from the Maldive Islands. These specimens differ from C. andamanense in their much lower, more obscurely defined, and more widely spaced spiral cords, with almost smooth interspaces, in their thicker but more weakly sculptured apertural lips, in having a weakly angling spiral cord on the centre of the sutural ramp, and in their paler and more varied external coloration (pale pinkish orange with white bands, to almost pure white).