Leptochryseus Al-Khayat & Jones, 1996

Ng, Peter K. L., Rahayu, Dwi Listyo & Naser, Murtada D., 2009, The Camptandriidae of Iraq, with description of a new genus and notes on Leptochryseus Al-Khayat & Jones, 1996 (Crustacea: Decapoda: Brachyura), Zootaxa 2312, pp. 1-26 : 16-21

Genus Leptochryseus Al-Khayat & Jones, 1996

Leptochryseus Al-Khayat & Jones, 1996: 798 .

Cleistostoma – Ng et al. 2008: 233 (part) (not Cleistostoma De Haan, 1833 ).

Type species. Cleistostoma kuwaitense Jones & Clayton, 1983 , by monotypy.

Diagnosis. Carapace average width to length ratio 1.32; quadrangular in outline, wider than long; dorsal surface moderately convex, without visible ridges dorsally, regions not well demarcated, epigastric region granular, gently convex, separated by longitudinal groove, gastro-cardiac groove shallow but visible ( Figs. 7 A, 8, 11G). Anterolateral margin of carapace unarmed, gently tuberculate; dorsal surface posterior to external orbital tooth depressed; posterolateral margin convex, distinct dorsolateral margin present; posterolateral margin sinuous; posterior carapace margin gently sinuous, with distinct submarginal ridge of granules ( Figs. 7 A, 8, 11G). Front with anterior margin gently concave from dorsal view, entire; frontomedial portion not projected, margin vaguely bilobed ( Figs. 7 A, 8, 11G). Supraorbital margin gently sinuous, notch separating it from base of front indistinct ( Figs. 7 A, 8, 11G); infraorbital margin receded, on orbital shelf, inner infraorbital tooth triangular, not separated from rest of margin by notch or fissure, suborbital ridge well developed, protruding beyond infraorbital margin, visible dorsally, suborbital sulcus adjacent to suborbital ridge, separating infraorbital margin from suborbital ridge. Epistome longitudinally narrow, interantennular septum broad, posterior medial tooth short, broad ( Figs. 7 B, 11 H). Pterygostomian region with deep, relatively broad Y-shaped sulcus. Third maxilliped merus with outer margin rounded, expanded beyond outer margin of ischium, inner margins thick; merus with anteroexternal margin produced to form small lobe; inverted, distinct V-shaped groove on outer part; ischium with inner distal angle produced, with row of submarginal setae along distal margin; outer surface of basal segment of palp concave, forming spatulate structure ( Fig. 11 I). Chelipeds equal; sexually dimorphic in large adult males; dactylus of male chela with distinct molariform tooth on cutting edge; finger tips in both sexes spatulate Fig. 11 J), more developed in females. Ambulatory legs relatively broad; ventral margins of P 3, P 4 meri with sharp spines; P 2–5 meri laterally flattened, expanded, appears foliaceous in smaller males, females; large males with disproportionately long P 3, merus, propodus very long, slender, ventral margin of dactylus with tuft of setae ( Figs. 7 A, 8). Male abdomen with subtruncate somite 1, not reaching P 5 coxae, separated by part of thoracic sternite 8; somite 2 subequal to width of somite 1; somites 2–5 immobile, sutures between somites incomplete to shallow; somite 5 broadly hexagonal with gently convex lateral margins; somite 6 immobile or with limited mobility in somite 5 although suture still present; telson free ( Figs. 7 B, 9 B, 10 B, C). G 1 gradually recurved, no distinct junction between recurved, proximal portions, tip broad, truncate, with strong, robust, subterminal spines on one edge ( Fig. 11 K, L).

Remarks. Jones & Clayton (1983) originally placed this species in Cleistostoma on the basis of these characters: the convex lateral margins of the carapace which are broader than long; operculiform third maxillipeds with the merus as long as, or longer than ischium; stout chelae in males; absence of tufts of setae between legs; reflexed G 1; and male abdomen with six somites and telson. None of these characters are useful at the generic level, and a re-examination of the material on hand indicates that not all the male abdominal somites are free. The description and figure by Jones & Clayton (1983: 187, fig. 2 i) of the male abdomen are incorrect. The male abdominal somites 2–5 are functionally fused even if parts of the suture are visible ( Figs. 7 C, 9 B, 10 B). The median sutures are visible but the lateral parts are very shallow; and even between somites 4 and 5, where the suture is relatively more prominent, somites 2–5 cannot be flexed ( Fig. 7 C, 9 B).

Al-Khayat & Jones (1996) subsequently argued that C. kuwaitense should be referred to a new monotypic genus, Leptochryseus , with the following comments: “Originally diagnosed as Cleistostoma by Jones and Clayton (1983), but now excluded, since all abdominal segments are free ….. Leptochryseus is also distinguished from Manningis and other related genera, since the first abdominal somite reaches the coxae of the fifth pereopods, but is not wider than remaining abdominal somites” ( Al-Khayat & Jones 1996: 798, 799). As discussed earlier, the male abdominal somites 2–5 are in fact fused. With regards to male abdominal somite 1 reaching the coxae of the P 5, this is also incorrect. The sides of the male abdomen are lined with setae, which obscure the surfaces of the sternites. Male abdominal somite 1 is not much wider than the next few somites but there remains a clear gap between the edge of this somite and the P 5 coxae ( Fig. 10 B). Ng et al. (2008: 234) commented that Leptochryseus Al-Khayat & Jones, 1996 , was only a junior synonym of Cleistostoma De Haan, 1833 , and retained the name Cleistostoma kuwaitense . They based their decision on the diagnostic characters provided by Al-Khayat & Jones (1996), which, as has been discussed above, are wrong.

Comparisons of C. dilatatum De Haan, 1833 (type species of Cleistostoma De Haan, 1833 ) with C. kuwaitense , however, now indicate that Leptochryseus can be recognised by using a different suite of characters not previously reported. In C. dilatatum , the lateral edges of male abdominal somite 1 taper to form a distinctly triangular structure and reach beyond the edge of the P 5 coxae, partially covering part of it ( Fig. 10 A). In L. kuwaitensis , the lateral edges of the male abdominal somite 1 are more truncate and less wide, not reaching the P 5 coxae. As a result, a part of thoracic sternite 8 remains exposed between the edge of male abdominal somite 1 and the P 5 coxae ( Fig. 10 B). The structure of the G 1 is also distinct. In C. dilatatum , the G 1 apex is drawn out into a point and has long, slender mushroom-like tubercles positioned subterminally on one edge ( Fig. 11 E, F). The G 1 apex is broad and truncate in C. kuwaitense , with strong, robust, spines situated subterminally on one edge ( Fig. 11 K, L). These characters argue for recognizing Leptochryseus Al-Khayat & Jones, 1996 , as a genus distinct from Cleistostoma De Haan, 1833 .

The close similarity between Nasima Manning, 1991 , and Leptochryseus , as well as their possible synonymy, has been discussed at length under the remarks of the previous genus.

Comparative material. CHINA: Cleistostoma dilatatum ( De Haan, 1833) : 2 males (14.7 x 20.4 mm, 16.3 x 22.9 mm), 2 females (13.6 x 19.6 mm, 14.2 x 20.1 mm) ( ZRC 1965.71.15.59– 62), Yangmatao, Shantung Peninsula, no date; 1 male (19.5 x 28.3 mm), 1 female (19.2 x 30.6 mm) ( ZRC 2000.9), Hebei, Tangu, coll. 23 July 1913. SOUTH KOREA: 8 females (10.0– 15.4 mm x 14.5–22.6 mm) ( RMNH D 39236 ), in mud, Asan Bay, Yellow Sea, on west coast, southwest of Seoul, coll. C. Swennen, 9 September 1989.