(1) Larva with following peculiarities. Mouth apparatus is specialized for carnivorism: mandibles lost their asymmetry, each mandible is shortened perpendicular to axis of articulation, with stout incisor and kinetodontium, prostheca is lost [see Heptagennota (7)], mola lacks grater; superlinguae are lost; maxilla lacks apical-ventral setae, its biting margin is shortened, with 2 canines (instead of three initial ones), proximal dentiseta [see Bidentiseta (1)] is strongly enlarged and looks as a wide dentate sclerotized plate (Kluge 2004: Fig.52:E) (similar modifications of mouthparts occur in some other specialized predators). Labial palp [2-segmented – see Heptagennota (8)] with strongly widened, nearly round 1^st segment (unlike Radulapalpata, this segment is flat, and muscles situated in it are not thickened – Kluge 2004: Fig.52:F). Larval body is flattened, pronotum has unique structure (Kluge 2004: Fig.52:A): lateral lobes are expanded far posteriorly, overlapping mesonotum and partly fused with it (that somewhat resembles Ecdyonurus/fg2); mediad of these lobes, posterior margin of pronotum forms a pair of cavities opened backward; margins of cavities bear numerous fine setae; fore protoptera are spread. Larval legs are adopted for inhabitancy on sandy ground: long; tarsus arched; claw are very long, slender, slightly arched, without denticles. Tergalii have unique structure: besides fibrillose lobe [see Branchitergaliae (3)] each tergalius II–VII has a ventral process arising near middle of lamellate lobe.

(2) Patella-tibial suture (initially present on middle and hind legs) is lost on all legs of larva [see (1)], subimago and imago (non-unique apomorphy – see Index of characters [1.2.18]).

Plesiomorphies of Pseudiron. Imaginal and subimaginal furcasternal protuberances are contiguous at anterior part and diverge only at posterior part, inside which metathoracic nerve ganglion is situated [see Heptagennota (4)] (Kluge 2004: Fig.52:B). 1^st tarsal segment is fused with tibia (in contrast to Pentamerotarsata) and non-shortened. Penis has no sclerites peculiar for Pentamerotarsata. Maxillary palp is 3-segmented. In contrast to Pentamerotarsata, submentum is well-developed (Kluge 2004: Fig.52:F). In contrast to Pentamerotarsata, larva completely retains primary siphlonuroid swimming specialization: abdomen is large, caudalii with dense long primary swimming setae (only in distal part segments are elongate and lack setation), without secondary swimming setae. Paracercus is subequal to cerci.