Shell small, rounded, posterior end short, chisel-shaped, distinctive bevelled extension of right valve overlaps dorsal margin of left valve; umbo small, pointed, with dorsal margins sloping equally on either side; rostrum continuous with long sloping posterior dorsal margin, ventral rostral margin short, slightly sinuated, anterior and ventral margins rounded; shell relatively thicker than those of most other small cuspidariids; innumerable fine concentric striae, angulate at ventral rostral ridge; ventral rostral ridge extends from umbo to ventral posterior corner of rostrum, dorsal rostral ridge runs approximately parallel and close to posterior dorsal margin of left valve, but more distant in overlapping right valve; elongate, triangular, anterior and posterior lateral hinge teeth of right valve correspond with grooves in left valve; resilifer small, extends posteriorly; resilium oblique. Maximum shell measurements are: length, 5.5 mm; height, 4.4 mm. Rhinoclama abrupta differs in a few small respects from other described species of the subgenus. A second type of gland cell is present that has not been recorded previously. Thus, in addition to the large familiar subepithelial gland cells filled with small pale granules, there are a series of very large flask-shaped cells, filled with large granules that stain yellow or bluish in Azan triple stain, of a similar appearance to lacunal cells. These are interspersed among the subepithelial gland cells and are present in the mantle edge from the anterior adductor to the siphons. Each cell opens onto the inner surface of the inner mantle fold by a single duct. While the subepithelial gland cells secrete an acid polysaccharide the flask-shaped cells do not stain with Alcian Blue and presumably secrete basic or neutral material. Their function is not clear.

Limited to two stations off the coast of Namibia. Depth range: 619-1014 m