On a New Genus and Species of Xanthid Crab (Crustacea: Decapoda: Brachyura) from Chesterfield Island, Coral Sea

u 17 December 1993 PROC. BIOL. SOC. WASH. 106(4), 1993, pp. 705-713 ON A NEW GENUS AND SPECIES OF XANTHID CRAB (CRUSTACEA: DECAPODA: BRACHYURA) FROM CHESTERFIELD ISLAND, CORAL SEA Peter K. L. Ng Abstract.—A new genus and species of xanthid crab, Cranaothus deforgesi, is described from Chesterfield Island. Cranaothus appears to be closely related to Paramedaeus, Metaxanthops, Macromedaeus, Medaeops, Neoxanthops, Glyptoxanthus and Lipaesthesius, but differs in the form and sculptures on the carapace, as well as structures of the sternum, male abdomen and male first pleopod. The larger cheliped of Cranaothus also possesses a specialized basal cutting tooth on its dactylus. A collection of Brachyura from Chester eroded vermiform granulated ridges; front field Island was deposited in the Museum distinctly produced; lobes truncatiform, national d'Histoire naturelle (MNHN), Par separated by deep fissure extending to epi is, by ORSTOM (Institut Francais de Re gastric region; external orbital angle low, in cherche Scientifique pour le Developement distinct, not clearly demarcating beginning en Cooperation). Among these specimens of anterolateral margin, joining series of was an interesting crab from Chesterfield smaller granules curving gently downwards Island with several peculiar features distin below supraorbital margin, across subor guishing it from all other known genera and bital region and towards buccal cavity; an species in the family Xanthidae MacLeay, terolateral margin not lobulated or toothed, 1838 (sensu Guinot 1978). anterior % arcuate, posterior xh subparallel The description of this new genus and to median longitudinal carapace axis; pos species forms the text of the present paper. terolateral margins gently concave. Ster- Abbreviations G1 and G2 are for the male nites 2-4 broad, sternal suture 1 and 2 com first and second pleopods respectively. plete, sternal sutures 2 and 3, and 3 and 4 Measurements are reported in millimeters, interrupted medially. Chelipeds distinctly in the sequence carapace width by carapace asymmetrical, fingers sharp, without pig length. mentation, larger cheliped with pronounced molariform basal cutting tooth on dactylus. Lateral margins of fused male abdominal Systematic Account segments 3-5 entire, continuous; segment 7 semicircular, lateral margins strongly con Family Xanthidae MacLeay, 1838 vex, tip rounded. (sensu Guinot, 1978) Type species. — Cranaothus deforgesi, new Subfamily Euxanthinae Alcock, 1898 species, by monotypy. (sensu Serene, 1984) Etymology.—The generic name is de Cranaothus, new genus rived from the Greek "kranaos" for "rugged Diagnosis.— Carapace quadrate, regions and rocky" (alluding to the eroded carapace not well defined; dorsal surfaces with very surface), in arbitrary combination with a fi small squamiform granulations; branchial, nal syllable of many xanthid genera. Gender gastric, cardiac and intestinal regions with masculine. 706 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Remarks.— In its external features Cra The carapace shape of Cranaothus is per naothus, new genus, appears to be closest haps closest to Neoxanthops, especially in to the genus Paramedaeus Guinot, 1967; species like N. cavatus (Rathbun, 1907) however, it differs in that the anterolateral which also has ridges on the dorsal surface. margin is not cut into distinct teeth (weak In N. cavatus, however, the frontal lobes are or otherwise), the front is very produced and separated only by a shallow cleft, not a deep lamellar, with the median fissure very deep; fissure, and the anterolateral margin is cut sternites 2-4 distinctly broader, sternal su into distinct lobes. The Gl of Cranaothus ture 1 and 2 being distinct (absent in Para is also proportionately shorter, with a dif medaeus), sternal suture 2 and 3 interrupted ferent shape, and the distal part is tapered medially (entire in Paramedaeus); male ab and very slender, compared to that of typ dominal segment 7 semicircular in shape ical Neoxanthops (see Serene 1984: figs. 127, (distinctly triangular in Paramedaeus); dis 128). Neoxanthops cavatus is not a typical tal part of the Gl is long, slender and strong member of Neoxanthops and should prob ly tapering, the tip being relatively sharp ably be transferred to a new genus. It differs (distal part stout and tip rounded in Para markedly from the type species of the genus, medaeus) (Guinot 1967, Serene 1984). N. lineatus Milne Edwards, 1867, in many With regard to the shape of the carapace, aspects, viz. the anterolateral margin grad Cranaothus resembles Indo-West Pacific ually becomes more obscure and gently genera such as Metaxanthops Serene, 1984, curves to end below the orbits, and does not Macromedaeus Ward, 1942, and Neoxan- meet the external orbital angle or supraor thops Guinot, 1968, but differs in many key bital margin; the frontal margin is not dis aspects. The front margin of Cranaothus is tinctly produced beyond the internal angle somewhat similar to that of Metaxanthops, of the supraorbital margin; the anterolateral with two broad and truncate lobes separated margin is not distinctly cristiform; the sur by a deep median fissure. Metaxanthops face is more distinctly domed, distinctly however, differs from Cranaothus in having sculptured, appears eroded, and instead of well developed and distinct epibranchial gently convex and completely smooth; the teeth and a much smoother carapace sur fingers of the chelipeds are very short in face. The general shape of the Gl in Meta stead of pigmented; and the subdistal part xanthops, although similar, is distinctly of the Gl has only a few short, simple hairs, stouter and the distal part is not slender and moderately long, setose hairs. tapering (Serene 1984: fig. 129). The an Cranaothus also differs from Macrome terolateral margin of Cranaothus resembles daeus, Neoxanthops and Metaxanthops in Macromedaeus nudipes (Milne Edwards, that the dactyls of the larger cheliped have 1867), but the structure of the front is dif a molariform basal cutting tooth absent in ferent, with the lobes more sinuous and less the other genera. projected forward in Macromedaeus. In With regard to the sculpturing on the car Macromedaeus, the two frontal lobes are apace surface, Cranaothus somewhat re also separated only by a cleft, without the sembles the genus Glyptoxanthus Milne Ed deep fissure present in Cranaothus. While wards, 1873-1881, which is represented in the regions are well defined in Macrome the Indo-West Pacific region by G. mean- daeus, they are only vaguely so in Crana drinus (Klunzinger, 1913). The anterolat othus. .The Gl of Cranaothus differs sub eral margin of Glyptoxanthus, however, is stantially from those of Macromedaeus, cut into distinct teeth, the front is not pro being proportionately shorter, stouter and jecting but is about level with the orbits, the different in shape (Serene 1984: figs. 101— frontal lobes are not separated by a deep 104). fissure, the dactylus of the cheliped lacks the VOLUME 106, NUMBER 4 707 special basal cutting tooth, and the last male the Xanthinae (cf. Neoxanthops, Metaxan- abdominal segment is distinctly triangular, thops, Macro medaeus). The genus is placed with a sharp tip and the lateral margins al in the Euxanthinae based on the absence of most straight (Odhner 1925: pi. 4 fig. 1, a clearly defined anterolateral margin be Guinot 1979: pi. 6 fig. 7). In Cranaothus, hind the external orbital angle in Crana the last male abdominal segment is semi othus, with the row of granules curving along circular. There is also some resemblance to the suborbital region toward the buccal cav crabs of the genus Medaeops Guinot, 1967, ity. although the shapes of the carapaces differ. Interestingly, Medaeus granulosus (Has- Cranaothus deforgesi, new species well, 1882) has a weak basal cutting tooth Figs. 1-3 on the dactyls of the chelipeds. Paramedaeus noelensis. — ? Serene & Umali, The shape and form of the carapace of 1972:68, pi. 7 figs. 7-9 [nee Paramedaeus Cranaothus also bears a marked similarity noelensis (Ward, 1934)]. to an eastern Pacific monotypic genus, Li- paesthesius Rathbun, 1898, represented by Material examined. — Holotype male L. leeanus Rathbun, 1898. Like Crana (carapace 8.0 by 5.9 mm), (MNHN), Ches othus, the surface of the carapace in Li- terfield Island, Coral Sea, station 144, paesthesius is covered by many small gran 19°27.73'S, 158°23.28'E, ca. 50 m depth, ules, forming uneven patterns. Lipaesthesius sand and Halimeda algae substrate, dredge, differs from Cranaothus in the following as leg. B. Richer de Forges, 30 Aug 1988. pects: point of attachment of antennal fla- Description of holotype male.— Carapace gellum concealed by upper margin of basal regions not well defined, grooves separating segment (point of attachment of flagellum gastric and branchial regions shallow, 2F, distinct and not concealed in Cranaothus); 1M, 3M regions low but discernible, 4M granule patterns on dorsal surface of cara indistinct, L and R not defined; H-shaped pace not vermiform; front not produced for groove separating cardiac and gastric regions ward and without deep median cleft; pos distinct; dorsal surfaces covered with very terolateral margin strongly concave (more small squamiform granulations; branchial, so than in Cranaothus), forming distinct gastric, cardiac and intestinal regions with "waist"; junction between antero- and pos uneven eroded ridges, forming vermiculat- terolateral margins not clearly demarcated, ed pattern; pterygostomial, suborbital

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