12 letters

hastiliarius buccellarius cancellarius cubicularius veterinarius stationarius quaternarius lanternarius stercorarius confessarius frumentarius serpentarius ballistarius tumultuarius Stradivarius professorius ascriptitius Trapizuntius

13 letters

suppositicius tetrabrachius microbrachius palimbacchius Rotundifolius Graminifolius linearifolius gastrocnemius ∙ Trigonogenius primiscrinius beneficiarius cornicularius clavicularius elemosinarius scorpionarius oculomotorius adscriptitius

14 letters

acephalopodius Stenopterygius caeremoniarius quaestionarius angusticlavius

15 letters

acephalocardius carcinoscorpius sesquiplicarius protospatharius ∙ penintentiarius vagoaccessorius

16 letters

acephalobrachius ichthyophthirius

19 letters

spinotransversarius

Words with a ∙ are valid Scrabble words (SOWPODS word list)