Holotype: length 6.6 mm, width 3.3 mm; Largest paratype: length 6.2 mm, width 2.8 mm; Smallest imature paratype: length 6.0 mm, width 2,8 mm.

Natal Bay, Brazil.

The shell is small (maximum length 6.6 mm) and lanceolate. The spire is high and acute, consisting of five or six dorsoventrally flattened postnuclear whorls. The suture is impressed but is obscured by varical buttresses. The body whorl is comparatively large for the genus and broadly fusoid. The aperture is moderately small and ovate, with a weakly developed anal sulcus. The outer apertural lip is moderately thickened and nonerect; its inner surface bears six very weak denticles. The columellar lip is entirely adherent. The siphonal canal is short, narrowly open, and dorsally recurved.
The body whorl bears two major lateral varices and, in some cases, a weaker third one ventral to the left lateral. Additional axial sculpture consists of four moderately weak costae in each intervarical space. Spiral sculpture consists of four moderately weak cords on the body and two or three on the canal. Where each body cord intersects a costa, a single pustule is developed. Earlier whorls show the typical six varices of the genus.
The shell is translucent milk-white, covered with a flat-white, minutely cancellate intritacalx in which the spiral elements appear to be continuous but are really discontinuous transverse tubes within the chalky layer.
The radular dentition and the operculum of this species are unknown; all specimens were empty when collected.
Radwin & D'Attilio, 1976. (Original description)

A. morchi resembles the robust Galapagan form of A. pyramidalis but differs from it in its small size at maturity and its minutely cancellate intritacalx. The small size of A. morchi may cause it to be confused with the other Brazilian species, A. cryptica. A. morchi differs from A. cryptica in its more robust, less flattened shell, its much more strongly cancellate intritacalx sculpture, and in its sculpture of spiral rows of distinct pustules.
Radwin & D'Attilio, 1976.