Shell quite broad and well sized for the genus. Reaches 21.6 mm in length, although most specimens measure around 18 and 19 mm. Solid and thick shelled in construction. The protoconch is small and raised, eroded in most shells. It is perfect in paratype 3 and there we see the two and a half protoconch whorls are white in color. We consider the start of the first axial wave as the start of the protoconch whorls, which are initially white in coloration. A chocolate pattern starts around the 3th or 4th teleoconch whorls. The total number of teleoconch whorls is quite impressive: they number 8 in the paratype 3. The whorls are covered by axial waves, set almost in the perfect prolongation of each other and giving the impression of so many solid ribs which they are not. The color pattern consists of a white band on the periphery of each whorl. The white extends up¬wards and downwards on top of each of the axial waves. There is a thin spiral band of white points on the lower half of the body whorl. The rest of the shell is a dark chocolate brown. The inside of the aperture has a slightly paler brown, with a thick glossy and smooth columellar side. Parietal channel well developed with a pale colored knob on the upper part of the aperture. Outer side of the aperture with the typical "Clavus"-flap, a little crenulate at the periphery in some shells. The siphonal canal is broad and shallow.

TYPE LOCALITY
Mindanao. Cagayan. 20-35 m.
DISTRIBUTION
At present only known from the Philippines but from quite some different islands: Palawan, Mindanao (north), Olango Island, Cebu and Bohol.

This beautiful species is definitely closest to Clavus viduus (Reeve, 1845). The type of C. viduus has been figured not so long ago by Higo et al. (2001) and is in the BMNH, London. It measures 19.6 mm. C. viduus is also found in the Philippines and has been well documented in Philippine Marine Mollusks, Vol. 2 on plate 674. Clavus isowai n. sp. can be distinguished in a glance from C. viduus by the presence of a thin white band on the periphery of the body whorl, while in C. viduus the upper half, including the periphery, is all white. The aperture in C. isowai n. sp. is small, and the outer aperture has a straighter shape. The parietal canal is pronounced in C. isowai n. sp., and has a big white knob of callus on its upper side. In C. viduus the canal is hard to notice and the callus knobs are absent. Another feature that will distinguishs both species at once is the color of the upper whorls: in C. viduus these are mainly white, with a very thin brown area above the suture. In C. isowai n. sp. the upper whorls have a broad chocolate dark brown band below the suture.