Perinereis Kinberg 1865

Key to species of Perinereis Kinberg, 1865 belonging to ‘ aibuhitensis ’ group

1. Ridges of area VI distally and sub-medially coalesced (areas VI-V-VI ridge pattern λ-shaped)......................... 2

- Ridges of area VI distally separated from each other (areas VI-V-VI ridge pattern π-shaped).......................... 5

2. Distal dorsal ligule distinctly short in posterior parapodia, projecting barely beyond notoaciculae............................................................................................... P. babuzai (Hsueh, 2019) (Taiwan)

- Distal dorsal ligule of medium length in posterior parapodia, projecting distinctly beyond notoaciculae................. 3

3. Area VI with short bars (broad-petite bars); area II with paragnaths arranged in distinct crescentic rows; area III without laterally isolated paragnaths........................................... P. linea (Treadwell, 1936) (Xiamen, China)

- Area VI with at least one long bar (smooth bar); area II with paragnaths arranged in oval patch; area III with laterally isolated paragnaths........................................................................................... 4

4. Area V with usually one paragnath (rarely none); area VI with long bars (smooth bars) only; distal region of dorsal ligule bluntly rounded in anterior parapodia; distal region of dorsal ligule projecting beyond median ligule in posterior parapodia................................................................... P. singaporiensis (Grube, 1878) (Singapore)

- Area V with usually three paragnaths (seldom 1–4); area VI with short and long bars (smooth and broad-petite bars); distal region of dorsal ligule conical in anterior parapodia; distal region of dorsal ligule subequal to median ligule in posterior parapodia....................... P. khambhatiensis Prajapat, Villalobos-Guerrero & Vachhrajani, sp. n. (Western India)

5. Area VI with long bars (smooth bars); area III without laterally isolated paragnaths; areas VII–VIII with anterior band having a medial patch of many tiny paragnaths................... P. vancaurica (Ehlers, 1868) (Nicobar Islands, Andaman Sea)

- Area VI with short bars (broad-petite bars); area III with distinct laterally isolated paragnaths; areas VII–VIII with anterior band lacking medial patch of tiny paragnaths.................................................................... 6

6. Areas VII–VIII with anterior band having only one furrow row................................................. 7 Areas VII–VIII with anterior band having two rows (one on furrows and one on ridges)............................. 9

7. Distal dorsal ligule not projecting beyond notoaciculae in medial and posterior parapodia; neuroacicular ligule extending markedly beyond median ligule in posterior parapodia; area III with 36 paragnaths........................................................................................... P. vitabunda (Pflugfelder, 1933) (Sumatra, Indonesia)

- Distal dorsal ligule markedly extending beyond end of notoaciculae throughout; neuroacicular ligule subequal to or slightly shorter than median ligule in posterior parapodia; area III with up to 31 paragnaths................................. 8

8. Ligules in anterior parapodia slender, acuminate; postero-dorsal tentacular cirri reaching chaetiger 2.................................................................................. P. kinmenensis (Hsueh, 2019) (Kinmen, China)

- Ligules in anterior parapodia thickened with blunt tip; postero-dorsal tentacular cirri reaching chaetiger 4–5.................................................................................... P. aibuhitensis (Grube, 1878) (Palau)

9. Neuroacicular ligule projecting markedly beyond ventral ligule in posterior parapodia; distal dorsal ligule shorter than median ligule throughout body; proximal dorsal ligule longer than distal dorsal ligule............................................................................................ P. belawanensis (Pflugfelder, 1933) (Sumatra, Indonesia)

- Neuroacicular ligule subequal to or slightly shorter than ventral ligule in posterior parapodia; distal dorsal ligule subequal to or barely shorter than median ligule throughout body; proximal dorsal ligule subequal or shorter than distal dorsal ligule.... 10

10. Area I: 7–8; area III: 48–65; area VII–VIII: 57–58; blade of heterogomph falcigers with incurved terminal tooth equaling half of total blade length; postero-dorsal tentacular cirri reaching chaetiger 3.... P. shigungensis (Hsueh, 2019) (Shigung, Taiwan)

- Area I: 1–3; area III: 18; area VII–VIII: 33; blade of heterogomph falcigers with incurved terminal tooth equaling one-third to two-fifths of total blade length; postero-dorsal tentacular cirri reaching chaetiger 1..................................................................... P. rookeri de León-González & Goethel, 2013 (Florida, northern Gulf of Mexico)