Neastacilla, Tattersall, 1921

King, R. A., 2003, Neastacilla Tattersall, 1921 redefined, with eight new species from Australia (Crustacea: Isopoda: Arcturidae), Memoirs of Museum Victoria 60 (2), pp. 371-416 : 374-375

Key to Australian and New Zealand species of Neastacilla

* Species known only from this sex.

1. Head with distinct dorsal tuberculation(s) or elevations(s) ........................................... 2

— Head dorsally smooth or with small rounded elevation 14

2. Fusion of head and pereonite 1 indicated by a suture.. 3

— Fusion of head and pereonite 1 without a suture..... 4

3. Anterolateral margin of pereonite 1 extended laterally, head and pereonites 1–4 with large prominent branch–like elevations, pereopods 2–4 flattened Neastacilla tharnardi

— Anterolateral margin of pereonite 1 not extended laterally, head and pereonites 1–4 with very small anteriorly produced elevations, pereopods 2–4 cylindrical (male extremely elongate and elevations reduced to blunt tubercles)................... Neastacilla attenuata

4. Pereonite 4 with large, prominent dorsal elevation(s).. 5

— Pereonite 4 smooth or with small dorsal elevation(s).. 7

5. Pleotelson equal to or longer than pereonites 5–7; pereonite 4 with proximal dorsal elevations (female pereonite 4 widened at midlength)......................... 6

— Pleotelson shorter than pereonites 5–7; pereonite 4 with dorsal elevations at midlength (female pereonite 4 not laterally widened at midlength)...................................... Neastacilla marrimarri (female)*

6. Pereonite 4 with large proximal dorsal elevation with 3 apices and 2 large lateral elevations; pleotelson with 2 pairs of lateral wings and widening distally to taper to a pointed apex (male pereonite 4 with single dorsal elevation proximally)................. Neastacilla tuberculata

— Pereonite 4 with large dorsal midlength elevation with 2 apices with 2 large lateral elevations; pleotelson with 1 pair of lateral wings, not widened and sharply tapered to a bluntly rounded apex....... Neastacilla tarni (female)

7. Pereonite 4 constricted (in dorsal view) for first third length..................................... 8

— Pereonite 4 not constricted (in dorsal view) for first third length.................................... 10

8. Pereonite 4 extremely elongate (10 times as long as pereonite 3 length).. Neastacilla inaequispinosa (male)

— Pereonite 4 not extremely elongate (less than 10 times pereonite 3 length)............................9

9. Pereonite 4 with dorsal and lateral elevations at midlength; pereonites 5–7 with a pair of dorsal elevations plus lateral elevations; pleotelson wider than pereonite 7, with 2 pairs of acute lateral wings.... Neastacilla fusiformis (male)*

— Pereonite 4 with a pair of small anterodorsal round tubercles; pereonites 5–7 smooth; pleotelson not wider than pereonite 7, with pair of blunt lateral wings.................................... Neastacilla tarni (male)

10. Head and pereonite 4 each with a pair of distinct spine–like elevations (male with elevations reduced to blunt tubercles)..................... Neastacilla lawadi

— Head and pereonite 4 smooth or with weak/ blunt elevations.................................. 11

11. Pereonite 4 without elevations; pleotelson longer than pereonites 5–7.............................. 12

— Peronite 4 with dorsal elevations; pleotelson not longer than pereonites 5–7.......................... 13

12. Pleotelson apex acute; antenna 2 peduncular article 5 as long as article 4......... Neastacilla soelae (female)*

— Pleotelson apex truncate; antenna 2 peduncular article 5 slightly shorter than article 4.......................................... Neastacilla algensis (female)*

13. Pereonite 4 with dorsal rounded tubercles extending laterally at midlength; pleotelson as long as pereonites 5–7, with 2 distinct blunt lateral wings....................................... Neastacilla sheardi (female)*

— Pereonite 4 with a weak dorsal elevation at midlength; pleotelson longer than pereonites 5–7, without defined lateral wings...... Neastacilla inaequispinosa (female)

14. Fusion of head and pereonite 1 defined with a suture..............................................15

— Fusion of head and pereonite 1 not defined with a suture...............................................19

15. Eye large and triangular shaped; pleotelson with an apical blunt notch...................... Neastacilla levis

— Eye small, round or oval in shape; pleotelson without apical blunt notch........................... 16

16. Pleotelson with large, acute lateral wings with an acute apex....................... Neastacilla monoseta

— Pleotelson without defined lateral wings, apex blunt. 17

17. Pereonite 4 not more than 6 times as long as pereonite 3, almost square in dorsal view (male without strong tuberculation and pereonite 4 not square in dorsal view)................................ Neastacilla antipodea

— Pereonite 4 extremely elongate (greater than 8 times as long as pereonite 3), not square in dorsal view...... 18

18. Pereonite 4 with a pair of distinct dorsal elevations proximally (female with pereonite 4 laterally expanded and upturned at midlength, male pereonite 4 narrow and constricted (in dorsal view) for first third length.................................. Neastacilla coonabooloo

— Pereonite 4 dorsally smooth (female with slight lateral expansion of pereonite 4 at midlength).......................................... Neastacilla deducta

19. Adult size 3–4 mm; pereonite 4 with a dorsal elevation at midlength (males with pereonite 4 constricted (in dorsal view) proximally but with dorsal elevation at first third length)........................ Neastacilla yuriel

— Adult size> 7 mm; pereonite 4 without dorsal elevations. .......................................... 20

20. Head with horizontal unsutured groove below eye; pleotelson with defined lateral wings (female pereonite 4 with anterolateral extensions)........ Neastacilla macilenta

— Head without horizontal unsutured grove; pleotelson without defined lateral wings....................... 21

21. Pereonite 4 elongate (greater than 8 times as long as pereonite 3); pleotelson with a truncated apex..................................... Neastacilla kanowna

— Pereonite 4 around 6 times as long as pereonite 3; pleotelson bluntly rounded........................................... Neastacilla tattersalli (female)*