Danielea, Ng & Clark, 2003

Ng, Peter K. L. & Clark, Paul F., 2003, Three new genera of Indo-West Pacific Xanthidae (Crustacea, Decapoda, Brachyura, Xanthoidea), Zoosystema 25 (1), pp. 131-147 : 141-142

Genus Danielea n. gen.

TYPE SPECIES. — Medaeus noelensis Ward, 1934 , by present designation.

ETYMOLOGY. — The genus is named after Danièle Guinot, whose exemplary work on xanthoids formed the basis of the present study. Gender feminine.

DIAGNOSIS. — Carapace quadrate, regions defined, with shallow grooves separating most regions; entire dorsal surface covered with small uniformly sized rounded to squamate granules, surface appears squamiform. Front weakly produced, bent downwards and inwards, inner supraorbital tooth low, rounded; orbits subparallel to frontal margin. External orbital tooth very low, almost undiscernible, no crest or row of granules connecting it to rest of anterolateral margin; anterolateral margin arcuate, with first lobe very low, uneven and three more low but more prominent triangular lobes, separated by shallow clefts. Posterolateral margin gently convex to almost straight. Basal antennal segment relatively narrow, rectangular, fitting tightly in orbital hiatus. Chelipeds with outer surfaces covered with uniformly sized rounded to squamate granules, surface appears pearliform, neither eroded or rugose; fingers shorter than palm, tips sharp; larger (usually right) chela with large, gently curved basal cutting tooth on cutting edge of dactylus. Ambulatory legs short, merus not cristate. Lateral margins of fused male abdominal segments 3-5 entire, continuous; telson semicircular, lateral margins gently convex, tip rounded. G1 distal part lined with long plumose setae.

REMARKS

The current generic position of Medaeus noelensis is unclear. Workers subsequent to Guinot (1967a, b, 1968) have discussed the problem but did not systematically resolve it. Serène (1968), Sakai (1976), Takeda (1978), Ribes (1978) and Thomassin (1978) have all wrongly regarded it as a species of Paramedaeus Guinot, 1967 . This species was however excluded from a list of species of Paramedaeus by Guinot (1971) and Serène (1984: 87, 90), while retaining the taxon in Paramedaeus , questioned its generic validity by discussing the similarities of P. noelensis with Cycloxanthops cavatus . Recently Ng (1993: 712), in comparing P. noelensis to Cranaothus deforgesi Ng, 1993 , noted that while it could not be referred to Cranaothus it was possibly not a true Paramedaeus species either.

Direct comparisons of specimens with P. simplex (A. Milne Edwards, 1873) , the type of Paramedaeus , confirm the necessity of separating M. noelensis into a new genus. The carapace shapes and various structures of the two species differ significantly, with P. simplex (see Serène 1984: pl. XIIC) being a more squarish species compared with the rectangular carapace of M. noelensis (see Serène 1984: pl. XIIF). The basal antennular segment in P. simplex is broad and squarish, whereas that of M. noelensis is narrow and rectangular. The basal antennal segment in P. simplex does not completely fill the orbital hiatus but in M. noelensis , the basal antennal segment fits tightly into the hiatus. The front of M. noelensis is short because the frontal margin folds downwards and inwards, giving the margin a folded appearance. In P. simplex , the front is flat, lamelliform and not folded. The male abdomen of P. simplex and P. noelensis differ markedly, with segment 7 in P. simplex being narrow, distinctly triangular, and the lateral margins gently concave or almost straight, while in P. noelensis , it is proportionately broader, the lateral margins are distinctly convex, and is more rounded. There is also a distinct cleft on each side present between segments 3 and 4 in P. noelensis absent in P. simplex . The G1 of M. noelensis ( Fig. 4 E-G) ( Serène 1984: fig. 51) is also proportionately shorter and slightly stouter than that of P. simplex and does not have the elongated distal part characteristic of the species ( Serène 1984: fig. 50). Although the anterior thoracic sternal plastron of both P. simplex and M. noelensis are similar, the other differences observed here strongly suggest that P. simplex and M. noelensis are not congeneric. Therefore a new genus Danielea n. gen. is here established for Medaeus noelensis .

As noted by Ng (1993), Danielea noelensis n. comb. seems to be allied to Cranaothus deforgesi , but the two cannot be regarded as congeneric mainly because in Danielea noelensis n. comb., there a proportionately distinctly wider space between thoracic sternal sutures 2 and 3, and 3 and 4; the second male abdominal segment has no transverse ridges; and the male telson is distinctly triangular in shape (against rounded). In addition, other differences include the generally smoother carapace surface of Danielea noelensis n. comb. which has no granulated vermiculations with the regions more distinct; the front is normal in D. noelensis n. comb. (against lamellar, strongly produced anteriorly with a deep median fissure in Cranaothus ); the posterolateral margin is almost straight to gently convex (against prominently concave in Cranaothus ); the outer surfaces of the chelipedal carpus are less rugose; the lateral edges of the fused male abdominal segments 3 and 4 have a distinct cleft on each side (against entire in Cranaothus ); and the distal part of the G1 does not possess a long projection.

Paramedaeus noelensis was assigned by Serène (1984: 20) to the Euxanthinae . The form of the anterolateral margin (with the anterior part gradually sloping downwards via the subhepatic region to meet the infraorbital margin) suggests that Danielea n. gen. should be attributed to subfamily Euxanthinae as defined by Serène (1984: 72).

Figures

FIG. 4. — Danielea noelensis (Ward, 1934) n. comb., holotype 6.4 mm, cw 4 mm, Christmas Island (NHM 1935.5.21.9); A, orbit and antennae; B, anterior thoracic sternites; C, right third maxilliped (setae not drawn); D, abdomen; E, G, distal part of left pleopod 1; F, pleopod 1. For all structures, minute granules not drawn. Figures F and G after Forest & Guinot, 1961. Scale bars: A, 0.5 mm; B-D, 1.0 mm; E, 0.01 mm.