Key to 20 known species of Anguillosyllis

1A. Palps free dorsally (may appear fused ventrally) or fused halfway with distal half or tips obviously free................. 2

1B. Palps fused completely, at most only a minor medial notch on anterior end of fused palps........................... 11

2A. Aciculae distally emergent........................................ Anguillosyllis aciculata n. sp. (South China Sea)

2B. Aciculae never emergent............................................................................... 3

3A. Adults with 10 setigers................................................................................. 4

3B. Adults with 11 setigers................................................................................. 6

4A. Palps fused halfway; with large posterior lobes on parapodia.............. Anguillosyllis denaria n. sp. (South China Sea)

4B. Palps entirely free or may be basally fused ventrally, with or without posterior parapodial lobes....................... 5

5A. Without posterior lobes on parapodia; setae with very long shafts up to 3x blade length, anterior dorsum not biannulate.................................................................... Anguillosyllis taleola n. sp. (South China Sea)

5B. With small posterior lobes on posterior setigers, setal shafts do not exceed 1.5–2x blade length; anterior dorsum slightly biannulate.................................................... Anguillosyllis carolina n. sp. (western North Atlantic)

6A. Palps fused for half to three-quarters length, tips clearly free................................................... 7

6B. Palps free to base dorsally, may be joined by thin membrane ventrally........................................... 8

7A. Palps fused only halfway, tips broad and rounded................. Anguillosyllis truebloodi n. sp. (central Pacific, CCFZ)

7B. Palps fused more than halfway, tips slim and pointed................... Anguillosyllis capensis Day, 1963 (South Africa)

8A. Falcigers with hooked tips (e.g., Figs.1H, 3 F–G, 14B)........................................................ 9

8B. Falcigers with blunt or pointed tips (e.g., Figs. 7D, 24 B–C)................................................... 10

9A. Anterior setigers 1–3 with 50 or more setae, all but two or three blades are short falcigers..................................................................................... Anguillosyllis hampsoni n. sp. (western North Atlantic)

9B. Anterior setigers 1–3 with maximum of 20–25 setae, including short falcigers and several spiniger-like setae with long fine tips............................................. Anguillosyllis palpata (Hartman, 1967) (Antarctica, widespread)

10A. Anterior setigers with 30–50 falcigers and 2–4 spiniger-like setae, number of setae per parapodium decreases to 16–20 in posterior setigers............................................... Anguillosyllis acsara n. sp. (western North Atlantic)

10B. Anterior setigers with 20–22 setae, posterior setigers with 10–12 setae........ Anguillosyllis hadra n. sp. (South China Sea)

11A. (Note three choices.) Palps completely fused; adults with 8 setigers............................................. 12

11B. Palps completely fused; adults with 9 setigers.............................................................. 13

11C. Palps completely fused; adults with 10 or 11 setigers........................................................ 15

12A. Peristomium 1.5x length of prostomium, fused palps with narrow anterior margin. Anguillosyllis andeepia n. sp. (Antarctica)

12B. Peristomium shorter than prostomium, fused palps with rounded, slightly notched anterior margin................................................................................. Anguillosyllis bruneiensis n. sp. (South China Sea)

13A. Posterior parapodia with large posterior lobes.................... Anguillosyllis pupa (Hartman, 1965) (western Atlantic)

13B. Posterior parapodia without posterior lobes................................................................ 14

14A. Parapodia with 4 aciculae, with large internal glands.................. Anguillosyllis enneapoda n. sp. (South China Sea)

14B. Parapodia with 2 aciculae, without internal glands.............. Anguillosyllis inornata n. sp. (eastern Pacific, California)

15A. Adults with 10 setigers, tips of posterior aciculae never emergent.............................................. 16

15B. Adults with 11 setigers, tips of posterior aciculae emergent........... Anguillosyllis hessleri n. sp. (central Pacific, CCFZ)

16A. Shafts of compound setae extremely heterogomph, some anterior setigers triannulate.......................................................................................... Anguillosyllis elegantissima n. sp. (South China Sea)

16B. Shafts of compound setae not extremely heterogomph, anterior setigers never triannulate........................... 17

17A. Parapodia with small posterior lobes................................ Anguillosyllis lanai Barroso et al., 2017 (Brazil)

17B. Parapodia without posterior lobes....................................................................... 18

18A. Anterior dorsum (setigers 1–2) biannulate....................... Anguillosyllis blakei n. sp. (eastern Pacific, California)

18B. Anterior dorsum not biannulate...................................... Anguillosyllis sepula n. sp. (South China Sea)