Hexalaughlia, Guinot, 2006

Guinot, Danièle, 2006, Rediscovery of the holotype of Paeduma cylindraceum (Bell, 1859) and description of a new genus of Hexapodidae (Decapoda, Brachyura), Zoosystema 28 (2), pp. 553-571 : 562-566

Genus Hexalaughlia n. gen.

( Fig. 4 )

Paeduma – Manning & Holthuis 1981 pro parte: 173, 174. Non Paeduma Rathbun, 1897: 163 (substitute name for Amorphopus Bell, 1859 ).

Thaumastoplax – Rathbun 1909: 113; 1910: 346, 347. — Tesch 1918 pro parte: 238, 239. — Sakai 1935 pro parte: 195; 1939 pro parte: 577, 578; 1976: 553, 555. — Imaizumi 1959 pro parte: 276. — Dai & Yang 1991 pro parte: 393, 419. Non Thaumastoplax Miers, 1881 (type species by monotypy: T. anomalipes Miers, 1881 ).

Paeduma – Karasawa 1990 pro parte: 25. — Huang et al. 2002 pro parte: 652, table 1. — Schweitzer & Feldmann 2001 pro parte: 332, 345.

TYPE SPECIES. — Thaumastoplax orientalis Rathbun, 1909 , by present designation.

OTHER SPECIES INCLUDED. — Thaumastoplax chuenensis Rathbun, 1909 .

ETYMOLOGY. — It is a pleasure to dedicate this new genus to Dr Patsy A. McLaughlin, in recognition of her considerable contribution to scientific knowledge. Gender: feminine.

GEOGRAPHIC DISTRIBUTION. — Western Pacific.

DESCRIPTION

Carapace wider than long, longitudinally convex, transversely flat. Dorsal surface with regions indistinct, except for a faint H-shaped median depression; gastric region may be sharply outlined.Lateral margin anteriorly arcuated, then straight (not diverging), sometimes marked by raised line. Antennae not covered by antennules. Front slightly deflected, thin. Epistome reduced. Orbits oval, in common straight line, not dorsally expanded, rimmed. Eyes movable, small, transversal, with small cornea. Buccal cavity much broader than long, anteriorly arcuated, sides anteriorly divergent. Mxp3 somewhat pediform, slender, inclined, gaping, leaving mxp2 only partly visible. Endopod with short, mesially expanded ischion; merus narrow, inclined; carpus short; propodus as long as broad, considerably dilated and with mesial expansion distally; dactylus lanceolated, with very long setae entering sternoabdominal cavity. A wide hiatus between palp and ischium, partly filled by fringes of setae. Exopod without flagellum. Pterygostomian region without row of stridulatory striae. Thoracic sternum wide. Sternites 1-2 forming wide, triangular piece extending between bases of mxp3, prolonging into sternite 3 without marked delimitation; sternite 4 much developed; sternites 5-7 similarly developed, high; sternite 8 reduced, visible dorsally only as minute plate inserted between sternite 7 and abdominal somite 1, most part hidden under carapace. Episternites 4-5 similarly elongated, pointed; episternites 6-7 similarly rounded, episternite 7 forming projection overhanging the posterolateral angle of carapace (interlocking apparatus). Sutures 4/5, 5/6 and 6/7 nearly equidistantly parallel. Sternal grooves or trenches absent in both sexes. Sternoabdominal cavity elongated, reaching sternite 3. Male abdomen very long, extending beyond bases of mxp3, moderately narrow, specially at level of somite 6and telson; no marked constriction at level of somite 6. Somites 1, 2 free, of about the same size, not much elongated transversally; somites 3- 5 fused in undivided piece, anteriorly narrowing; somite 6 as relatively long plate; telson relatively short, bluntly triangular. Abdomen not maintained by prominences of press-button type [to be verified], appearing maintained between oblique slopes of deep sterno-abdominal cavity. Gonopods concealed under abdomen, slender, recurved posteriorly, apex apparently naked. Chelipeds equal in male, short; palm of large cheliped higher than long, may be ornamented with granules.P2-P4 markedly unequal, with P3 granulous, very developed, longer, thicker (in particular the merus) than subequal, smooth P2, P4; all articles fringed with long, thick setae. No stridulating apparatus.

REMARKS

The recent discovery of the holotype of P. cylindraceum ( Bell, 1859) , type species of the American genus Paeduma , has allowed its comparison with two other species described from Thailand and referred to Paeduma by Manning & Holthuis (1981: 173). As a result, a new genus, Hexalaughlia n. gen., is established for those two species: H. chuenensis ( Rathbun, 1909) n. comb., and H. orientalis ( Rathbun, 1909) n. comb.

Hexalaughlia n. gen. may be distinguished from Paeduma by the following characters: mxp3 pediform, slender, endopod recurved, with dilated ischium and propodus, and exopod without flagellum ( Fig. 4A ) (mxp3 operculiform, endopod with narrow propod, exopod with flagellum in Paeduma , Fig. 2C ); stridulating striae lacking (row of oblique striae in Paeduma , Fig. 2A, C ); thoracic sternum with sternites 1-3 forming a triangular piece, without marked delimitation ( Fig. 4B ) (a narrow triangle in Paeduma , Fig. 2B ); male abdomen markedly wider in Hexalaughlia n. gen. than in Paeduma (where it appears somewhat linear); somite 6 moderately long, without constriction in Hexalaughlia n. gen. ( Fig. 4 B-D) (somite 6 as very long, narrow, basally constricted plate in Paeduma ,

A

Figs 1B ; 2B ); telson rather short, bluntly triangular in Hexalaughlia n. gen. (elongated and rounded at tip in Paeduma ); chelipeds equal in Hexalaughlia n. gen. (strong heterochely in Paeduma ); P2-P4 markedly unequal, with P3 stout, much larger than P2 and P4, ornamentated with strong granules in Hexalaughlia n. gen. (P2-P4 subequal, nearly similar in size and shape, and weak ornamentation in Paeduma , Fig. 1 ).

Contrary to Manning & Holthuis’ (1981) assertion, Paeduma does not resemble Thaumastoplax . In contrast, Hexalaughlia n. gen. is close to Thaumastoplax by its pediform and recurved mxp3 ( Fig. 4A ), the absence of a flagellum on mxp3 exopod, absence of stridulating pterygostomian striae, and unequal P2-P4. Hexalaughlia n. gen., however, differs from Thaumastoplax by the narrower carapace; the relative size of the ambulatory legs, the P2 and P4 being subequal and P3 much stouter (P2 slender, P3 very stout and P4 thicker than P 1 in Thaumastoplax ); G1 recurved posteriorly and 8- shaped (slender, only sinuous, with apex directed anteriorly in Thaumastoplax ).

Figures

FIG. 4. — Hexalaughlia?orientalis (Rathbun,1909) n. comb.,♂ 5.5 × 8 mm, Japan,Albatross, stn 4964,27.VIII.1906,37 fms,det.Thaumastoplax orientalis (USNM 46392): A, mxp3 (flagellum of exopod not shown);B-D, different views of thoracic sternum and abdomen. Abbreviations: a1-a6, abdominal segments 1-6; c, carapace;cx1-cx4, coxae of P1-P4; e4-e7, épisternites 4-7; p, projection of sternite 4; s8, exposed portion of sternite 8; t, telson; 1-7, sternites 1-7; 4/5-6/7, thoracic sternal sutures 4/5-6/7. Scale bars: 2.5 mm.

FIG. 2. — Paeduma cylindraceum (Bell, 1859), holotype ♂ 15.3 × 23.5 mm, dry, “Gallapagos [sic] Mr Cuming” (OUMNH 15693): A, frontal view; B, different views of thoracic sternum and abdomen; C, mxp3 and stridulating striae; D, proximal articles of left P4, with apodemal platelet; E, posterior view of thoracic sternum to show reduced sternite 8. Abbreviations: a.p., apodemal platelet; a1-a6, abdominal segments 1-6; bc, carapace border; bi, basis-ischion; c, carapace; cd, articular condyle of cx4 on thoracic sternite 7; co, constriction at level of abdominal somite 6; cx1-cx4, coxae of P1-P4; e4-e7, épisternites 4-7; m, merus; p, projection of sternite 4; s8, exposed portion of sternite 8; t, telson; 1-7, sternites 1-7; 4/5-6/7, thoracic sternal sutures 4/5-6/7. Scale bars: 2.5 mm.

FIG. 1. — Paeduma cylindraceum (Bell, 1859), holotype ♂ 15.3 × 23.5 mm, dry, with two Bell’s handwritten labels: “Amorphopus” and “Am: cylindraceus male sign. Gallapagos [sic] Mr Cuming” (OUMNH 15693): A, dorsal view, showing apodemal platelets of P4 coxae (indicated by arrows); B, ventral view.