Shell medium sized for the subgenus, up to 12.2 mm in height at maturity. Height/width ratio 1.5-1 -7. Broadly ovate, weakly spinose, lightly built. Subsutural ramp narrow, weakly sloping on spire whorls, broader, strongly sloping on last teleoconch whorl, weakly concave. Shell entirely white.
Spire high with 1.5 protoconch whorls and up to 4.15 broad, convex, angular, strongly shouldered, weakly spinose whorls. Suture impressed. Protoconch large, broad, whorls rounded, smooth, maximum width 900-1000 µm. Terminal lip weakly raised, narrow, prosocline.
Axial sculpture of teleoconch whorls consisting of low, narrow, weakly webbed lamellae, more strongly developed at shoulder, producing short, narrow, broadly open spines at intersection of lamellae and primary spiral cords. First whorl with 6 or 7 lamellae, second with 7 or 8, third 7-9, fourth 6-9, last (apertural) with 6-7. Spiral sculpture of high, rounded, narrow, weakly squamous, primary cords, low, narrow secondary cords and numerous, narrow, low threads. First teleoconch whorl with P1 and P2, broadly separated by a large gap, second whorl with P1 and P2, starting weak s1 and one or two threads, third whorl with PI and P2, weak s1 and narrow, weak threads of various strength, fourth and last whorls with P1, sl, P2, P3, P4, (s4), P5, (s5), P6, s6, adp and several threads of different magnitude.
Aperture small, ovate. Columellar lip broad, flaring, smooth or occasionally with one or two weak knobs abapically, rim partially erect, adherent at adapical extremity. Occasionally with weak, very low parietal tooth at adapical extremity. Anal notch shallow, broad. Outer lip weakly erect, smooth with four weak or moderately strong, broad denticles within: D1, D2, D3, D4-D5 fused. Siphonal canal short, broad, weakly dorsally recurved, broadly open. Operculum ovate, light brown with apical nucleus. Radula muricine with broad rachidian bearing long, narrow, central cusp; short, triangular lateral denticles, almost half the size of central cusp; broad, long, triangular lateral cusps. Marginal area short, occasionally with small marginal denticle, almost indistinct when present. Marginal cusp short, outwardly bent. Lateral teeth sickle shaped, long, with broad base.

Flexopteron akainakares differs in many ways from F poppei and does not need to be compared here.
Flexopteron primanova was described from northern Madagascar but F. akainakares n. sp. is not sympatric, living more to the South. Flexopteron akainakares differs in having a relatively smaller shell, a higher and larger protoconch (900-1000 wide and 900 µm high vs 850-900 wide and 700-800 µm high) with rounded first whorl vs flat in F. primanova, markedly shorter shoulder spines on the last teleoconch whorl in adult specimens, a shorter siphonal canal, a different morphology of the primary spiral cords of the teleoconch whorls, and a last teleoconch whorl with P1, sl, P2, P3, P4, (s4), P5, (s5) and P6, with a broad gap between P1 and P2 as opposed to P1, P2, (s2), P3, P4, P5, (P6).
The radula of F. primanova is also different in having a very long, narrow central cusp, narrow lateral denticles approximately half the size of the central cusp, long, narrow, lateral cusps even longer than the central cusp, a smooth marginal area and acute, moderately long, marginal cusps.
The operculum is similar, being ovate with an apical nucleus.

TYPE LOCALITY. — South Madagascar, Manantenina sector, 24°23>S, 47°32,E, 307-319 m [ATIMO VATAE: stn DW3524]. DISTRIBUTION. — South Madagascar, taken alive at 184-203 m, shells at 203-424 m.