(modified from Jimi et al. 2017)
1 Body papillae abundant, short, giving a velvety appearance.................................................... 2
- Body papillae scarce, long, tunic looks bare............................................ Diplocirrus sp. Sri Lanka
2(1) Body without sand particles............................................................................. 3
- Body with sand particles.............................................................................. 11
3(2) Ventrolateral gonopores present in some anterior chaetigers.................................................... 4
- Ventrolateral gonopores absent........................................................................... 9
4(3) First chaetiger with long chaetae, about half as long as body width; caruncle posteriorly expanded.......................................................................................... D. erythroporus Gallardo, 1968Vietnam
- Anterior end with short chaetae, 1/3–1/5 as long as body width; caruncle posteriorly tapered......................... 5
5(4) Branchiae with lamellae............................................................................... 6
- Branchia without lamellae.............................................................................. 7
6(5) Median chaetigers with neurochaetae tapered, 22–25 articles, and tip delicately falcate; cirriform branchiae with lamellae along basal 1/4–1/5 of each filament............................................ D. branchiatus (Rullier, 1965)Australia
- Median chaetigers with neurochaetae barely tapered, 8–11 articles, and tip markedly falcate; cirriform branchiae with lamellae along basal 1/3–1/2 of each filament.................................. D. nicolaji (Buzhinskaja, 1994)Russia, Japan
7(5) Dorsal branchiae as long as ventral ones; caruncle shorter than palp scar... D. mamoi Jimi, Fujiwara & Kajihara, 2017Japan
- Dorsal branchiae shorter than ventral ones; caruncle longer than palp scar............................................................................................... D. asamushiensis Jimi, Fujiwara & Kajihara, 2017Japan
8(3) Papillae digitate, longer than wide; chaetiger 1 with notochaetae fragile, if complete, as long as body width.............. 9
- Papillae hemispherical, about as long as wide; cephalic cage chaetae shorter than body width....................... 10
9(8) Median chaetigers with neurochaetae with articles slightly longer than wide; body brownish................................................................................................. D. capensis Day, 1961South Africa
– Median chaetigers with neurochaetae with articles 4–6 times longer than wide; body yellowish................................................................................... D. imajimai Jimi, Fujiwara & Kajihara, 2017Japan
10(8) Median chaetigers with 5–6 neurochaetae, shorter than notochaetae, with articles 2.0–2.5 times longer than wide.................................................... D. kudenovi Salazar-Vallejo & Buzhinskaja, 2011 Eastern Pacific Ocean
- Median chaetigers with 2–3 neurochaetae, about as long as notochaetae, with articles 7–8 times longer than wide........................................................... D. stopbowitzi Darbyshire & Mackie, 2009 Southern Irish Sea
11(2) Anterior chaetigers barely wider than following ones........................................................ 12
- Anterior chaetigers swollen, much wider than following ones................................................. 13
12(11) Some lateral papillae twice as long as in chaetal lobes................. D. rugosus Teixeira, Rizzo & Santos, 2015Brazil
- Lateral papillae shorter.............................................................. Diplocirrus sp. Morocco
13(11) Lateral papillae 1/25–1/5 as long as longest notochaetae..................................................... 14
- Lateral papillae 1/3–5/6 as long as longest notochaetae...................................................... 18
14(13) Ventrolateral gonopores present........................................................................ 15
- Ventrolateral gonopores absent......................................................................... 16
15(14) Cephalic cage well developed (2/3 as long as body width)............. D. ohtsukai Jimi, Fujiwara & Kajihara, 2017Japan
- Cephalic cage poorly developed (1/4 as long as body width)....... D. salazarvallejoi Teixeira, Rizzo & Santos, 2015Brazil
16(14) Cephalic cage well developed (as long as body width)....................................................... 17
- Cephalic cage poorly developed (1/3 as long as body width)......... D. tohokuensis Jimi, Fujiwara & Kajihara, 2017Japan
17(16) Neurochaetal rounded projection present in each article............ D. toyoshioae Jimi, Fujiwara & Kajihara, 2017Japan
- Neurochaetal rounded projection absent..................................... D. glaucus (Malmgren, 1867)Norway
18(13) Lateral papillae in chaetal lobe short (1/3 as long as notochaeta); anterior part (roughly corresponding to chaetigers 1–3) not pigmented............................................... D. incognitus Darbyshire & Mackie, 2009South Africa
- Lateral papillae in chaetal lobe long (5/6 as long as notochaeta); anterior part (chaetigers 1–3) with rusty pigments.................................................................... D. seisuiae Jimi, Fujiwara & Kajihara, 2017Japan