Syllinae (Polychaeta, Syllidae) from Australia. Part. 2. Genera Inermosyllis, Megasyllis n. gen., Opisthosyllis, and Trypanosyllis Author Martín, Guillermo San Departamento de Biología (Zoología), Laboratorio de Biología Marina e Invertebrados, Facultad de Ciencias, Universidad Autónoma de Madrid, Canto Blanco, 28049 Madrid, Spain. E-mail: guillermo. sanmartin @ uam. es, maite. aguado @ uam. es Aquatic Zoology, The Australian Museum, 6 College Street, Sydney, NSW, 2010 Australia. E-mail: pat. hutchings @ austmus. gov. au Author Hutchings, Pat Author Aguado, María Teresa Departamento de Biología (Zoología), Laboratorio de Biología Marina e Invertebrados, Facultad de Ciencias, Universidad Autónoma de Madrid, Canto Blanco, 28049 Madrid, Spain. E-mail: guillermo. sanmartin @ uam. es, maite. aguado @ uam. es Aquatic Zoology, The Australian Museum, 6 College Street, Sydney, NSW, 2010 Australia. E-mail: pat. hutchings @ austmus. gov. au text Zootaxa 2008 2008-08-01 1840 1 53 journal article 1175­5334 Key to Australian species of Opisthosyllis 1. Dorsum with numerous papillae ( Figs 28A, B ) .......................................................... Opisthosyllis viridis - Dorsum without papillae..............................................................................................................................2 2. Mid-posterior and posterior parapodia with thick, simple chaetae formed by enlarged shafts, blades absent.....................................................................................................................................................................3 - Without thick, simple chaetae..................................................................................................................... 4 3. Dorsal cirri slender, elongated ( Fig. 18A ), some longer than body width ............... Opisthosyllis japonica - Dorsal cirri relatively thick, shorter than body width ( Fig. 24A ) ......................... Opisthosyllis simpliseta 4. Dorsal cirri long, several times longer than body width ( Fig. 21 ). Compound chaetae all bidentate ......... ............................................................................................................................ Opisthosyllis longicirrata - Dorsal cirri similar in length to body width or slightly shorter ( Fig. 16A ). Midbody to Posterior compound chaetae unidentate .................................................................................................... Opisthosyllis brunnea