| Feature/species | P. australopatagonica M.L. Garcia, L.A. Villacis, Maidana & E. Morales | P. caballeroae V.H. Salinas, D. Mora, R. Jahn & N. Abarca * | P. decipiens E. Morales, G. Chavez & Ector | P. frankenae sp. nov. | P. laucensis Lange-Bertalot & Rumrich | P. parasitica (W. Smith) E. Morales | P. pseudoconstruens (Marciniak) D.M. Williams & Round |
| Valve dimensions (µm) | L: 20-25 W: 6.5-9.0 | L: 13.8-17.7 W: 6.9-8.5 | L: 4-29 W: 4-6 | L: 8.7-12.0 W: 6.7-7.7 | L: 5.5-20.0 W: 3.5-5.5 | L: 9-18 W: 4.5-5.0 | L: 4-22 W: 3-7 |
| Stria density (in 10 µm) | 10-12 | 13-14 | 13-15 | 14 | 14-15 | 19-21 | 15-18 |
| Valve outline; axial area; virgae | Cruciform to rhomboid with subcapitate apices; lanceolate, wider at central area, clearly depressed with respect to virgae in outer view, slightly depressed in internal view; much wider than striae | Cruciform with narrowly rounded ends; lanceolate, wider at central area; clearly depressed with respect to striae in external view; wide | Lanceolate with rostrate ends; lanceolate wider at central area, externally slightly depressed with respect to virgae, internally at the same level as the latter; wide | Cruciform with broadly rounded ends; lanceolate, wider at central area; clearly depressed with respect to striae in external and internal view; slender than striae | Lanceolate to rhomboid with narrowly subrostrate to cuneate ends; lanceolate, faintly depressed with respect to virgae in outer view, flat in internal view; wide | Lanceolate with narrowly rounded to subcapitate ends; lanceolate, wider at central area, clearly depressed with respect to virgae in external and internal view; as wide as striae | Cruciform with broadly rounded to subcapitate ends; lanceolate wider at central area, slightly depressed with respect to virgae in external and internal view; much wider than striae |
| Areolae; volae; striae | Round at apices to elliptically elongate; large generally growing opposite from shorter axis of areolae, internally forming a dendritic pattern; composed of 1-2 areolae on valve face, 1 large, round to ovoid on valve mantle | Round at apices to elliptically elongate, sometimes only 1 very long on valve face; smaller, bifurcate and growing from longer areolar axis; composed of 1-2 areolae on valve face, valve mantle areola not clearly illustrated | Round to ovoid; diapason shaped and further bifurcate at the valve interior, allowing the internal deposition of two concentric disks of inorganic material; composed of 1-2 areolae on valve face and 1 large, trapezoid on mantle, sometimes an extra round one present on mantle | Round to elliptic; smaller, bifurcate, allowing the internal deposition of an elliptic disk of inorganic material; composed of 1-4 areolae on valve face and a single, large, trapezoid one on mantle | Round to elliptic; developed with ring-like depositions distorted in different ways at the valve interior; composed of 1-2 areolae on valve face, decreasing in size toward axial area and a single, slightly larger, elliptic to trapezoid on the mantle | Round at apices to elliptically elongate; small, usually originating from smaller axis of valve; composed typically of 1, unusually 2, areolae on valve face, typically one smaller areola on valve mantle | Round to elliptic; smaller, bifurcate, originating from inner areolar perimeter; composed of 1-4 areolae on valve face, 1-2 on valve mantle, of same size as valve face areolae |
| Spines; stipules; flaps | Incipient, forming a short arch-like structure extending from virgae to virgae; absent; absent | Very thin, flattened, extending from virgae to virgae, forming an undulate to dentate pattern on valve face/mantle transition; absent; absent | Solid, elliptic base, as wide as basal vimen, flattened body with concave sides, spatulate or heart-shaped tip; absent; absent, only mineral depositions resembling floating disks on outer areolar opening | Solid, round to elliptic base, wider than basal vimen, triangular in side view, flattened upper body with bifurcate tip; absent; disk-like, 1 persistent in valve face areolae; 1-3 in mantle areolae | Incipient and occurring as whitish depositions along valve face/mantle transition; absent, absent | Absent; absent; absent | Solid, with long elliptic base, shorter than basal virgae on which they grow, flattened body with concave sides, highly branched tips; absent; absent |
| Apical pore fields; mantle abvalvar blisters | Cavernous and large, almost covering entire valve apex with poroids at the base of troughs, internally opening into a single elliptic depression; small, absent from the apices | Cavernous and large, almost covering entire valve apex with poroids at the base of troughs, internally unknown; excess depositions impede visualization in original illustrations | Cavernous, from 1 to several rows of poroids can be seen externally, internally a roundish depression contains several rows or poroids; developed, present including at valve apices | Cavernous, only one transapical row of poroids can be seen externally, internally, a round depression contains various rows of poroids; developed, present including at valve apices | Non-cavernous, sunken onto valve apex in external view, internal view unknown; small, not covering apices | Cavernous, visibly sunken onto valve apex and occupying almost its entirety, pores lie at bottom of troughs, internally plaque of pores is raised; very small and absent from apices | Very reduced externally, internally opening into a small depressed circular area; small and present at apices |
| References | Garcia et al. (2021) | Salinas et al. (2020) | Morales et al. (2012b) | This study | Servant-Vildary (1986), Rumrich et al. (2000) | Morales (2003a, 2010) | Williams and Round (1987) |