Loimia Malmgren 1866

Original diagnosis by Malmgren (1866: 380): "Corpus antice inflatum, postice attenuatum ventre subplano, dorso convexo. Branchiae, paria 3, arborescentes, posteriores gradatim minores, ramosissimae, ramulis ultimis brevissimis numerosissimisque. Fasciculi setarum capillarium a segmento quarto, h. e. tertio branchifero, incipientes in 17 segmentis. Setae capillares apice paulo curvato attenuato anguste limbatae. Tori uncinigeri a segmento secundo setigero incipientes, pone ultimum segmentum setigerum in pinnulas uncinigeras apice rotundatas mutati, per totum corpus obvii. Pinnulae uncinigerae deorsum vergentes per latera ventris plani decurrentes. Uncini pectiniformes 5-dentati, dentibus validis curvatis acuminatis, uniseriales, in segmento uncinigero septimo et novem sequentibus autem biseriales. Scuta ventralia antice conspicua."

Generic diagnosis by Lavesque et al. (2017: 936): "Branchiae on segments 2–4; lateral lappets on segments 1 and 3, 1 and 2/3 (in combination of segments 2 and 3) or 1, 3 and 4; ventral shields from segment 2 or 3; nephridial papillae on segments 3–4 and 6–8; 17 pairs of thoracic notopodia from segment 4; chaetae alimbate, unilimbate, symmetrical or asymmetrically bilimbate, smooth tipped; neuropodia from segment 5, uncini avicular or pectinate with a single vertical series of teeth, arranged in single rows on segment 5–10, in double rows, back to back, up to segment 20, and in single rows along the abdomen; pygidium sometimes with anal cirri or papillae."