Tutankhamen Rathbun, 1925

Mclay, Colin L., 2009, Revision of the crab genus Garthambrus Ng, 1996, with the description of two new genera and discussion of the status of Tutankhamen Rathbun, 1925 (Crustacea: Brachyura: Parthenopidae), Zootaxa 2122, pp. 1-50 : 39-40

Tutankhamen Rathbun, 1925

Tutankhamen Rathbun, 1925: 530 . – Gore & Scotto 1979: 62. – Ng et al., 2008: 132.

Type and only species. Mesorhoea cristatipes A. Milne-Edwards, 1880 , by original designation. Gender masculine.

Diagnosis. Carapace sub-triangular, broader than long, CW/CL ratio = 1.25, regions inflated; dorsal surface smooth; epibranchial margin expanded, partially covering ambulatory legs; not produced beyond base of abdomen; no lateral ventral depression. Rostrum spatulate. Postorbital angle slightly obtuse. Gastro-orbital notch absent. Hepatic margin not continuous with epibranchial region. Hepatobranchial notch present, distinct, broad. Epibranchial margin slightly convex, posterior one-seventh angled, angle acute; teeth triangular, narrow, U-shaped gaps present between adjacent teeth; last epibranchial tooth anterior to posterior margin, fused with preceding tooth. Proto-, meso- and metagastric regions differentiated, without ridge. Hepatic region slightly inflated, lower than epibranchial and gastric regions. Epibranchial region without continuous diagonal ridge.

Sub-orbital region without diagonal ridge, excavated laterally and mesially; suborbital margin gently curving. Epistome slightly depressed medially, anterior half with strong protruding lamelliform ridge, without protrusion below antennular article 1, lower margin broadly V-shaped. Pterygostomial region excavated, no distinct afferent channel. Pterygostomial ridge lamelliform, without dense setae covering afferent channel, not continuous with sub-epibranchial ridge. Distinct sub-hepatobranchial notch present. Sub-epibranchial region narrow, smooth. Posterior sub-branchial teeth absent.

Antennal article 3 long, nearly reaching anterior lateral corner of antennular article 1; anterior margin of antennal article 4 above antennular article 1 anterior lateral corner, shorter than antennal article 3.

Third maxilliped merus sub-quadrate, upper margin entire, anterior lateral corner expanded, anterior mesial corner with slight diagonal hiatus, carpal junction with indistinct hiatus; carpus outer surface with short distal spine, exposed; propodus outer surface with short distal spine, exposed; dactylus exposed; exopod exposed, tip partially hidden by merus anterior lateral corner, tooth on mesial margin at distal one-third.

Cheliped margins dentate to cristate, teeth relatively broad, broadly triangular; merus upper surface smooth; dactylus about 45º to manus central axis. Lamelliform projection on cheliped coxa.

Male thoracic sternum smooth, strongly depressed, forming inverted U-shape; transverse and longitudinal grooves absent. Male telson triangular, longer than broad. G1 relatively stout, tip rounded, not armed with long spines or stiff setae. G2 longer than G1; flagellum as long as basal section, twisted.

Remarks. The type species of this genus was originally placed in Mesorhoea Stimpson, 1871 , but bears no similarities to other species in that genus. Rathbun (1925) noted that the afferent channels of M. cristatipes A. Milne Edwards, 1880 , differed markedly from other Mesorhoea species being “shorter and deeper, bordered above by a laminar expansion of the hepatic and anterior branchial margins, below by a parallel lamina having an emargination near the beginning of the branchial regions; the canals terminate in a cul-desac behind the orbit and open on the epistome by a fissure between the external angle of the thin lamina which forms the anterior edge of the buccal cavity and a promontory formed by the infero-internal angle of the orbit. Epistome spacious and very concave, separated by a thin ridge and a considerable interval from the antennules.” It is not quite clear what Rathbun (1925) meant by “infero-internal angle” means and we presume that it refers to the inferior-internal angle. In addition she pointed out that the maxilliped merus does not have the antero-internal angle produced anteriorly unlike Mesorhoea sensu stricto. Rathbun (1925) created Tutankhamen to accommodate M. cristatipes .

Tutankhamen cristatipes is, however, morphologically similar to some Garthambrus species, in particular G. pteromerus (see Fig. 22 E–H). The similarities include a sub-triangular shaped carapace that is relatively smooth dorsally and the proximal half of the cheliped merus outer margin dentate, whereas the distal half of the cheliped merus outer margin is entire. The resemblance also extends to the similarly shaped G1 and G2. The G2, as in all Garthambrus species, is longer than the G1.

However, Tutankhamen is not congeneric with Garthambrus . Tutankhamen can be differentiated from Garthambrus by having a greatly expanded pterygostomial ridge. This ridge is entire and protrudes out so much that it is visible dorsally. In Garthambrus , the pterygostomial ridge is never visible dorsally. In Tutankhamen , there is a strong lamelliform process in the middle of the epistome. This lamelliform process is absent or reduced in Garthambrus . On the first antennular article of Tutankhamen , there is a strong crista of about the same length as that of the first antennal article, which is also parallel to the central axis of the carapace. This crista is absent in Garthambrus . In addition, the ambulatory leg dactyli are glabrous in Tutankhamen , but pubescent in Garthambrus .

Figures

FIGURE 22. Tutankhamen cristatipes (A. Milne-Edwards, 1880): A – D, holotype, male 16.9 x 13.5 mm (MCZ 8943), Caribbean Sea, off St. Vincent. — Garthambrus pteromerus (Ortmann, 1893): E – H, male 19.2 x 13.4 (ZRC), Philippines, Visayas, Bohol, Panglao, Balicasag I. A, E, carapace, dorsal surface; B, F, epistome; C, G, sternum and abdomen; D, H, side profile.