Carcinoplax, H. MILNE EDWARDS, 1852

Ng, Peter K. L. & Castro, Peter, 2020, A revision of Carcinoplax abyssicola (Miers, 1885) and seven related species of Carcinoplax H. Milne Edwards, 1852, with the description of two new species and an updated key to the genus (Crustacea, Decapoda, Brachyura, Goneplacidae), Zoosystema 42 (17), pp. 239-284 : 281-282

KEY TO SPECIES OF CARCINOPLAX H. MILNE EDWARDS, 1852

1. One well-developed, anteriorly curved anterolateral tooth posterior to outer orbital tooth on each side of carapace ( Guinot 1989: pl. 13, fig. F, as C. eurysternum Guinot & Richer de Forges, 1981 ) ................................. ..................................................................................................................... C. ischurodous (Stebbing, 1923) .

— Two anterolateral teeth posterior to outer orbital angle (1 or 2 anterolateral teeth may be greatly reduced or even obsolete in some large individuals) .............................................................................................................. 2

2. Adults attain large size (cl more than 30-40 mm), with reduced outer orbital and anterolateral teeth (obsolete in largest individuals), rounded anterolateral borders (carapace becoming almost spherical), and much enlarged chelipeds (P1) with conspicuously elongated meri, propodi ......................................................................... 3

— Adults do not attain large size (cl less than 30-40 mm), do not show progressive reduction in outer orbital (if present) and anterolateral teeth with corresponding rounded anterolateral borders and chelipeds (P1) with conspicuously elongated meri, propodi ............................................................................................................. 8

3. Low, conspicuous granules on carapace; small individuals with triangular, acute, curved, acute first and second anterolateral teeth ( Guinot 1989: pl. 1, fig. D); uniformly red to dark red-brown carapace in life, bright redbrown markings on chelipeds (P1) ............................................................... C. longimana (De Haan, 1833) .

— No conspicuous granules on carapace; small individuals with narrow, acute anterolateral teeth, or small, blunt first anterolateral teeth; in life, carapace not uniformly red or dark-red brown ............................................. 4

4. Small- to medium-size individuals with 2 narrow, acute, spine-like anterolateral teeth below acute, conspicuous outer orbital tooth on each side of carapace ( Guinot 1989: pl. 1, figs G, H; Hsueh & Huang 2002: fig. 6A); carapace nearly quadrate, with red, round spot on dorsal surface in most individuals when fresh ( Hsueh & Huang 2002: fig. 8B) ............................................................................................... C. indica Doflein, 1904 .

— Small- to medium-size individuals with blunt first anterolateral tooth, second tooth curved, acute; carapace globose; never with red spot on carapace in life ........................................................................................... 5

5. Outer orbital angle with low tooth or absent; second anterolateral tooth short, low (more conspicuous in small individuals), not hook-like .......................................................................................................................... 6

— Outer orbital angle with distinct tooth; second anterolateral tooth usually distinct, elongated, hook-like .... 7

6. P2-P5 relatively short; anterolateral teeth may be low in larger individuals but always visible ( Ng & Mitra 2019: fig. 6C, D); purple-red vertical band across carapace from front to posterior border in life ( Hsueh & Huang 2002: fig. 8C); western Pacific ............................................................................ C. purpurea Rathbun, 1914 .

— P2-P5 relatively longer; anterolateral tooth short, absent in large individuals ( Guinot 1989: fig. 9A-C; pl. 3, figs A, C, E); carapace uniformly colored in life; Red Sea and Persian Gulf ............. C. monodi Guinot, 1989 .

7. G1 with rounded, truncated tip ( Ng & Mitra 2019: fig. 8K, L, N); western Pacific ..... C. sinica Chen, 1984 . — G1 with pointed tip ( Ng & Mitra 2019: fig. 8E, F); Indian Ocean ................... C. mistio Ng & Mitra, 2019 .

8. Carapace, chelipeds (P1), and P2-P5 covered with conspicuous short setae ................................................. 9

— Carapace, chelipeds (P1), and/or P2-P5 may have sparse setae, short tomentum, or mostly or completely devoid of conspicuous setae, or tomentum ........................................................................................................... 10

9. Conspicuous, acute tubercles on proximal portion of P1 propodi (may be absent in large individuals) ( Hsueh & Huang 2002: fig. 5E); distal quarter of fingers darkly pigmented; acute tooth on distal portion of P2-P5 meri ( Chen 1998: fig. 4-2; Hsueh & Huang 2002: fig. 5C); no conspicuous color pattern in life …....................... ...................................................................................................................... C. spinosissima Rathbun, 1914 .

— Conspicuous, low, blunt tubercles on proximal portion of cheliped (P1) propodi ( Guinot 1989: pl. 6, fig. H); distal half of fingers darkly pigmented; distal portion of P2-P5 meri smooth; in life with orange reticulated lines on P1 and carapace (obvious when denuded) ............................................................. C. nana Guinot, 1989 .

10. Carapace, chelipeds (P1), and P2-P5 covered with short tomentum (large individuals only on ambulatory legs) ( Hsueh & Huang 2002: fig. 7A) ............................................................................ C. tomentosa Sakai, 1969 .

— Carapace, chelipeds (P1), and P2-P5 not covered with conspicuous short tomentum ................................ 11

11. Outer orbital angle without tooth or eminence; with 2 thin, spine-like anterolateral teeth ( Castro 2007: figs 4A, 5) ..................................................................................................................... C. tenuidentata Castro, 2007 .

— Outer orbital angle ends in lobe or tooth; anterolateral teeth not thin, spine-like ...................................... 12

12. Front with slight median notch ( Guinot 1989: fig. 17) .................................... C. confragosa Rathbun, 1914 . — Front straight, without distinct median notch. ........................................................................................... 13 13. Conspicuous, well-developed anterolateral teeth, with acute, anteriorly-oriented or hook-like tips ............ 18 — Relatively small, blunt, non-spinous anterolateral teeth ( Castro 2007: figs 7, 10) ...................................... 24

14. P2-P5 long, relatively slender, distal end of folded P5 merus extending beyond tip of second anterolateral tooth ......................................................................................................................................................... 15

— P2-P5 short, distal end of folded P5 merus only reaching or barely reaching tip of second anterolateral tooth .................................................................................................................................................................. 16

15. Two conspicuous, wide transverse ridges on dorsal surface of carapace ( Castro 2007: fig. 3); western Pacific .. ................................................................................................................................. C. cracens Castro, 2007 .

— Dorsal surface of carapace evenly convex, without transverse ridges; eastern Indian Ocean ............................. .................................................................................................................. C. longipes (Wood-Mason, 1891) .

16. Two conspicuous, wide transverse ridges on dorsal surface of carapace ............. C. inaequalis (Yokoya, 1933) . — Dorsal surface of carapace evenly convex, without conspicuous ridges. ...................................................... 17

17. All anterolateral teeth anteriorly curved; narrow, J-shaped gap between outer orbital tooth and first anterolateral tooth ( Castro 2009: fig. 1A); southwestern and central Pacific .............................. C. uncinata Castro, 2009 .

— Anterolateral teeth sharp but not curved (only first one in rare cases); outer orbital angle often prominent, rounded. ................................................................................................................................................... 18

18. Posterior margin of epistome with median part pronounced, triangular, lateral margins conspicuously concave ( Fig. 21D) ................................................................................................................................................. 19

— Posterior margin of epistome with truncated or nearly straight median part; lateral margins nearly straight or slightly sinuous ( Fig. 3D) .......................................................................................................................... 20

19. Two transverse elevations across cardiac, gastric regions of carapace ( Figs 21C, D; 22C, D); western Pacific ... ............................................................................................................................................... C. jugum n. sp.

— Dorsal surface of carapace evenly smooth, without transverse elevations; western Indian Ocean ..................... ...................................................................................................................... C. fasciata Ng & Kumar, 2009 .

20. Outer, proximal margin of cheliped carpus with sharp tooth; western Pacific and eastern Indian Ocean ......... .................................................................................................................................. C. polita Guinot, 1989 .

— Outer, proximal margin of cheliped carpus smooth, without tooth ........................................................... 21

21. P2-P5 proportionally short, stout, with distal end of folded P5 merus not reaching tip of second anterolateral tooth (e.g. Figs 10A; 11A; 19A; 20A) ........................................................................................................ 22

— P2-P5 proportionally long, slender, with distal end of folded P5 merus reaching tip of second anterolateral tooth (e.g. Figs 2A; 3A; 13A; 14A) ..................................................................................................................... 23

22. Posterior margin of epistome with median part not protruding ( Figs 19D; 20D); G1 elongated, distal half distinctly slender ( Fig. 25F); southwestern Pacific .................................................................... C. adelphia n. sp.

— Posterior margin of epistome with median part pronounced, protruding ( Figs 10D; 11D; 12D); G1 relatively short, stout ( Fig. 25A, B); northwestern Pacific ................................................. C. specularis Rathbun, 1914 .

23. Fingers dark brown or black almost along their entire lengths ( Figs 2H; 3I; 4H; 5H); inner distal angle of carpus of cheliped dentiform ( Figs 2E, F; 3F, 4F, 5E); Indian Ocean and southwestern Pacific .................................. ............................................................................................................................ C. abyssicola ( Miers, 1885) .

— Fingers dark brown or black along the distal two-thirds to half portions ( Figs 13I, J; 14H); inner distal angle of carpus of cheliped usually spiniform with tip narrow ( Figs 13F; 14F; 15E); western Pacific ............................ ........................................................................................................................... C. verdensis Rathbun, 1914 .

24. Outer, dorsal surface of cheliped (P1) propodi and carpi with conspicuous granular tubercles ( Castro 2007: fig. 8); P2-P5 relatively short ( Fig. 7), distal end of folded P5 merus only reaching tip of second anterolateral tooth; western Pacific ............................................................................................. C. tuberosa Castro, 2007 .

— Outer, dorsal surface of chelipeds (P1) smooth; P2-P5 proportionally long ( Castro 2007: fig. 10), distal end of folded P5 merus extending beyond tip of second anterolateral tooth; central and southwestern Pacific ........... ................................................................................................................................ C. velutina Castro, 2007 .