Shell solid, fusiform, consisting of six postlarval whorls, larval shell white, consisting of one smooth whorl. The first postlarval whorl has 7 fragile foliaceous varices that adhere to the protoconch; there is no intervarical node between these early varices. The regular adult sculpture starts on the second whorl and there are 3 varices and 3 intervarical nodes per whorl. The spiral sculpture consists of spiral cords, of which a few stronger ones extend on to the varices where they tend to produce spines; there are also extremely fine spiral threads which, together with the fine axial sculpture present on some specimens (including the holotype), may give a reticulate appearance under high magnification. Aperture oval, outer lip with 7 denticles; siphonal canal of moderate length for the genus, open; colour light tan with a few brownish blotches on the varices or the nodes; aperture white.
Dimensions: Height of the shell 21 mm, breadth 11 mm.

Shell up to 30 mm in length with 1.5-2 protoconch whorls, and 6 teleoconch whorls. Protoconch small, smooth. Whorls rounded. Axial sculpture of last teleoconch whorl with 3 thin, wing-like varices, extending to the middle of the siphonal canal. Other axial sculpture of one high, strong, intervarical node. Spiral sculpture of 4 or 5 low, weak, primary cords, more apparent on dorsal surface of varical wings, although still weak. Aperture small, roundly-ovate. Outer lip smooth, with 6 or 7 weak denticles within; denticles occasionally almost obsolete in some specimens. Columellar lip narrow, smooth, adherent. Siphonal canal long, narrow, open. Transluscent white or light tan with a few brownish blotches on varices or nodes. Aperture white.

T. atlantideus differs from T. leucas in its smaller larval shell, by having intervarical nodes and by its coloured shell. In T. leucas, there are several postlarval whorls with numerous varices (Fechter, 1977: fig. 11), while there are only 1 to 1.5 such whorls in P. atlantideus. P. leucas also reaches a larger size.

As already noted by Bouchet & Waren (1985: 147), P atlantideus differs from P leucas (Fischer, 1897) in its smaller size, in having no intervarieal axial sculpture, and mainly, in having a trivaricate shell sculpture from first or second postlarval shell, while P leucas has several postlarval whorls with numerous axial lamellae. P atlantideus differs from the West Atlantic P phaneus (Dall, 1889), and P havanensis Vokes, 1970, in having a larger shell, with broader wings, and a single, strong intervarieal node. P phaneus and P havanensis both lack or have lower, occasionally more numerous, axial nodes.

In addition to the material from the Azores , P. atlantideus is known from the Great Meteor Bank, in 295-343 m (Fechter, 1977 as P. leucas).