Guitonia Garth & Iliffe, 1992

Jr, Robert Murray Lasley, Mendoza, Jose Christopher E. & Ng, Peter K. L., 2010, Two new species of Guitonia Garth & Iliffe, 1992 (Crustacea: Decapoda: Brachyura: Xanthidae) from the central and western Pacific Ocean, Zootaxa 2684, pp. 1-13 : 1-3

Guitonia Garth & Iliffe, 1992

Type species. Guitonia troglophila Garth & Iliffe, 1992 , by original designation; gender feminine.

Diagnosis. Carapace broader than long, transversely ovate. Anterior regions granular; 2M, 3M defined by deep depressions. Front with 3 distinct recessed pits; one median, one on either side, separating front from orbital margin. Margin between orbit, first anterolateral tooth indiscernible or poorly defined by granular ridge. Anterolateral margins with 4 distinct teeth separated by marginal denticles, each with tip pointing anteriorly. Endostome without oblique ridges. Chelipeds unequal to subequal, tips of fingers crossing. Propodus of major chela with longitudinal furrow on upper margin; fixed fingers often with larger basal teeth, denticles along margin to tip; dactylus usually with 3 basal teeth, first may be enlarged. Ambulatory legs long, slender, combined length of carpus, propodus about same length as merus. Surface of thoracic sternum granular, sternites 1, 2 fused, forming triangular plate, suture between sternites 1, 2 indiscernible, suture between sternites 2, 3 distinct, suture between sternites 3, 4 deep laterally, only slightly indicated medially, sternite 4 with median longitudinal line, sternal press-button on sternite 5 midway between anterior, posterior sutures, or slightly nearer anterior. Male abdominal cavity deep, telson reaching or almost reaching imaginary line joining posterior edge of cheliped coxae. Male abdomen with 5 somites, including telson, somites 3–5 completely fused, telson subtriangular. G1 moderately stout, distal half twisted on vertical axis, tip recurved, ornamented with several stiff, simple subapical setae. G2 short, about one-third length of G1.

Remarks. The subfamilial placement of Guitonia Garth & Iliffe, 1992 , is not clear. Ng et al. (2008: 193) surmised that, based on current knowledge, the only significant difference between Xanthinae and Euxanthinae is that the “first anterolateral tooth (in Euxanthinae ) is separated from the exorbital margin such that the anterolateral margin is continued towards the anterior buccal cavity.” The general xanthine condition is observed in Guitonia ( Fig. 1 B, D, F). However, the condition is not easily discernible in Alainodaeus Davie, 1993 , and Monodaeus Guinot, 1967 , genera morphologically similar to Guitonia but currently placed in Euxanthinae . Ng et al. (2008: 193) also mentioned that a strongly differentiated basal tooth on the dactylus of the major chela is common in many euxanthine genera and that this character might be phylogenetically informative in differentiating between the two subfamilies. They listed several genera in which this character occurs. Many euxanthines, however, do not have this character, e.g. Euxanthus Dana, 1851 , Hypocolpus Rathbun, 1897 , Hepatoporus Serène, 1984 , and Glyptoxanthus A. Milne-Edwards, 1879 . Compounding the ambiguity of this character, some xanthine genera such as Marratha Ng & Clark, 2003 , Jacforus Ng & Clark, 2003 , some species of Xanthias Rathbun, 1897 , Nanocassiope Guinot, 1967 , Euryxanthops Garth & Kim, 1983 , and Paraxanthias Odhner, 1925 , possess a strongly differentiated basal tooth on the major chela ( Mendoza & Ng 2008). Guitonia troglophila does possess a differentiated basal tooth, whereas the only known specimen of G. leimomi n. sp., does not. However, this character can vary slightly in G. paulayi n. sp., which possesses a differentiated basal tooth (i.e. being distinctly robust relative to the other teeth) in 6 of 10 adult male and female type specimens. On the holotype of G. paulayi n. sp. (UF 1291), the basal tooth on the dactylus of the major chela is about half the size of that on a paratype specimen (UF 1967), whereas another paratype specimen (UF 1291) has an almost indiscernible tooth. Therefore, a clear decision on the subfamilial placement of Guitonia based on this character cannot be made, and the genus is retained in the Xanthinae for the time being. All three species of Guitonia share a highly conserved, granular, transversely-ovate carapace with similarly demarcated anterior regions, four similar anterolateral teeth that point anteriorly, three frontal recessed pits, and relatively long, slender ambulatory legs. They appear to form a distinct group and differ from other related genera as described below.

Guitonia is superficially similar to the euxanthine Alainodaeus Davie, 1993 , by virtue of the following features: 1) carapace transversely ovate, granular, with similar anterior regions indicated, and similar anterolateral and posterolateral dimensions; 2) subtriangular to triangular anterolateral teeth; 3) a distally curving male G1 sometimes with a lateral flange; and 4) long, slender ambulatory legs. However, it differs significantly in the following characters: 1) always with four anterolateral teeth, the last three of which are acute and pointing anteriorly ( Fig. 1 A, C, E) (lower, less acute anterolateral teeth with the first more reduced or absent in Alainodaeus ) ( Davie 1993: pls. 5A, 6A; Davie 1997: figs. 4a, 5a, 18b; Mendoza & Ng 2008: figs. 1, 2A, B); 2) a relatively long male telson ( Fig 2 B, 4B) (a relatively short male telson in Alainodaeus ) ( Davie 1993: figs. 5B, 6C; Davie 1997: figs. 4f, 5h; Mendoza & Ng 2008, fig. 4C); and 3) a more slender male G1 with a strongly recurved distal end ornamented with long subapical setae ( Figs. 2 C–E, 4C–E) (a stout, less curving male G1 lacking long subapical setae in Alainodaeus ) ( Davie 1993: figs. 5C, D, 6E–G; Davie 1997: figs. 4G, H, 5I, J; Mendoza & Ng 2008: fig. 4D, E).

There are several genera currently placed in the Xanthinae that bear a superficial resemblance to Guitonia (see Guinot 1967). Guitonia is similar to Micropanope Stimpson, 1871 , Gonopanope Guinot, 1967 , Coralliope Guinot, 1967 , and Nanocassiope Guinot, 1967 , in the general shape of their carapaces: transversely ovate, granular, and with similar regions. Guitonia differs from Micropanope ( Guinot 1967: 347, figs. 4, 1A–C), however, on the basis of the following features: 1) a relatively broad carapace ( Fig. 1 A, C, E) (narrower carapace in Micropanope ); 2) a relatively long anterolateral margin ( Fig. 1 A, C, E) (short anterolateral margin in Micropanope ); 3) a short front ( Fig. 1 A, C, E) (more projecting in Micropanope ); 4) four fully formed anterolateral teeth ( Fig. 1 A, C, E) (two distinct anterolateral teeth in Micropanope ); and 5) long, slender ambulatory legs ( Fig. 1 A, C, E) (relatively shorter and stouter in Micropanope ). Guitonia differs from Gonopanope ( Guinot 1967: 351, figs. 2, 6, 7) by virtue of the following features: 1) a broad carapace ( Fig. 1 A, C, E) (relatively narrow in Gonopanope ); 2) long anterolateral margins bearing four distinct teeth ( Fig. 1 A, C, E) (short anterolateral margins with only two distinct teeth in Gonopanope ); and 3) a less twisted distal end of the male G1 ( Figs. 2 C–E, 4C–E) (prominently twisted in Gonopanope ). Guitonia differs from Coralliope ( Guinot, 1967: 353, figs. 3, 11) by having the following features: 1) a broader carapace with long anterolateral margins bearing four distinct teeth ( Fig. 1 A, C, E) (relatively narrow with two or three anterolateral teeth in Coralliope ); 2) long, slender ambulatory legs ( Fig. 1 A, C, E) (relatively shorter, stouter in Coralliope ); and 3) a recurved male G1 with long, strait distal setae ( Figs. 2 C–E, 4C–E) (a straight male G1 with stout distal bristles in Coralliope ). Guitonia differs from Nanocassiope ( Guinot 1967: 355, figs. 8, 9, 12– 14; Davie 1997: 347) by having the following features: 1) a less twisted G1 ( Figs. 2 C–E, 4C–E) (highly twisted in Nanocassiope ) with long distal setae (stout bristles in Nanocassiope ); and 2) more acute anterolateral teeth ( Fig. 1 A, C, E) (more obtuse in Nanocassiope ).

Present in both G. troglophila and G. leimomi n. sp., are two granular ridges linked at the level of the exorbital angle and the first anterolateral tooth, which encloses a small, depressed area (visible in frontal view, Fig. 1 B, F). Both species also have reduced orbits and eyestalks, likely adaptations to their cavernicolous habitats. On the other hand, more characters are shared between G. leimomi n. sp., and G. paulayi n. sp. Both possess transverse rows of granules on the anterior regions of the carapace, which are basally conjoined and relatively conspicuous, the anterolateral teeth are spiniform (more lobate in G. troglophila , Fig 1 A, C, E), the front is nearly straight (angled posteriorly with a relatively large V-shaped notch in G. troglophila , Fig 1 A, C, E), and subequal, homomorphic chelae with smooth fingers of the minor chelae (unequal, dimorphic chelae with granular fixed fingers of the minor chela in G. troglophila ). The two latter species have the same general G1 shape, moderately stout, distally twisted and recurved, and ornamented with several long, simple subapical setae. Unfortunately, no males of G. troglophila are known and comparisons are not really possible at this time. The number of differences between G. leimomi n. sp., and G. paulayi n. sp., on one hand, and G. troglophila , on the other suggests that they may not be congeneric. This can probably only be resolved once male specimens of G. troglophila are found.

Figures

FIGURE 1. Guitonia leimomi n. sp., holotype male, 15.5 × 9.7 mm (ZRC 2010.0277), Hawaiian Is., A, dorsal view, B, frontal view; Guitonia paulayi n. sp., holotype male, 11.2 × 7.3 mm (ZRC 2010.0278), Guam, C, dorsal view, D, frontal view; Guitonia troglophila Garth & Iliffe, 1992, holotype female, 14.2 × 9.7 mm (LACM CR 19871671), Galápagos, E, dorsal view, F, frontal view.

FIGURE 2. Guitonia paulayi n. sp., holotype male, 11.2 × 7.3 (ZRC 2010.0278), Guam; A, right third maxilliped, external view; B, male abdomen, external view; C, left G 1 detail of tip, external view; D, left G 1, external view; E, left G 1, internal view; F, right G 2, external view. Scales: A – E, 1.0 mm; F, 0.5 mm.