Uca (Xeruca)

Shih, Hsi-Te, 2015, Uca (Xeruca), a new subgenus for the Taiwanese fiddler crab Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae), based on morphological and molecular evidence, Zootaxa 3974 (2), pp. 151-169 : 154-162

Uca (Xeruca) subgen. nov.

Uca (Thalassuca) Crane, 1975: 75 (part); Rosenberg 2001: 840, 848, 851 (part). Tubuca Bott, 1973: 322 (part).

Uca ( Tubuca )—Beinlich & von Hagen 2006: 10, 14, 15, 25 (part); Ng et al. 2008: 241 (part).

Type species. Uca formosensis Rathbun, 1921 , by present designation.

Etymology. From the Greek xeros for “dry,” for the high intertidal habitat of the type species, in arbitrary combination with the genus name Uca . Gender feminine.

Diagnosis. Carapace highly arched, branchial chambers strongly tumid; front narrow; anterolateral angles acute, produced forwards ( Figs. 2 A, C, 3 A, 4 A). Male with anterolateral margins long, strongly developed, almost straight; turning at an angle to join convergent, distinct, dorsolateral margins ( Figs. 2 A, C, 3 A, 4 A); female with anterolateral, dorsolateral margins strongly beaded, with definite boss or tuberculate swelling on carapace behind dorsolateral margin ( Fig. 2 E).

Suborbital crenellations rolled out in male, becoming minute or absent along outer angle; suborbital crenellations erect in female, becoming strong, truncate, separated, larger towards antero-external angle ( Fig. 2 B; Shih et al. 1999: fig. 1 E, F). Orbital floor with mound, pile in female, none in male; suborbital region, upper pterygostomian regions naked in male, setose in female ( Shih et al. 1999: fig. 1 E, F). Male without pleonal clasping apparatus in sterno-abdominal cavity.

Major cheliped with fingers laterally flattened, smooth; lower margin of pollex, upper margin of dactylus almost straight, not arched; cutting margins with distal half almost straight, without depression or enlarged teeth; proximal half with shallow elliptical space; furrows on external surface of fingers very faint or absent; outer surface of manus with low, well-separated tubercles ( Figs. 2 A, D, 3 B, 5 A). Male handedness 1: 1. Minor cheliped with fingers longer than manus, gape narrow, female with enlarged teeth in middle of gape ( Fig. 2 F), male without teeth in gape ( Fig. 2 G). Meri of second, third ambulatory legs moderately wide, dorsal margin of first, fourth meri almost straight in male ( Figs. 2 A, C, 3 A); dorsal margin of meri of ambulatory legs slightly convex in female ( Shih et al. 1999: fig. 1 B–D).

G 1 with pore moderately large; anterior flange very narrow, distal tip tapering, beyond the tip of inner process; posterior flange broad, slightly curved, much wider than pore; inner process long, broad, thick, bent forwards at right angles; thumb moderate length, not reaching base of flange ( Fig. 6). Female gonopore in shallow sternal depression, rimmed along postero-external quarter but not tuberculate ( Shih et al. 1999: fig. 3 E, F).

Urocardiac ossicles of gastric mill simple, median tooth with 2 pairs of similar transverse ridges, separated by gaps reached deeply near central ridge, on posterior tooth plate. 2 to 3 lower, weak pairs of cusps on stem region; stem region with widen middle part ( Fig. 7).

Remarks. The carapace of Xeruca subgen. nov. ( Fig. 4 A) features a highly arched and quadrate shape, with long and straight anterolateral margins and well-marked dorsolateral margins. Its carapace is similar to that of Australuca species ( Fig. 4 B–D), especially U. (Australuca) seismella Crane, 1975 ( Fig. 4 C), but the dorsolateral margins of Australuca are proportionately shorter. Adult Australuca species are smaller in size, with the largestsize species is U. (Australuca) elegans George & Jones, 1982 with CW 26.6 mm (cf. George & Jones 1982: 25) while in U. (Xeruca) formosensis , the largest CW is 34.9 mm (cf. Shih et al. 1999: 170). Tubuca species are different on account of their triangular carapaces ( Fig. 4 E, F), with shorter and convergent anterolateral margins, although U. (Tubuca) arcuata ( De Haan, 1835) ( Fig. 4 E) has long and straight anterolateral margins. The carapaces of Gelasimus species are also different, with oblique orbital margins in U. (Gelasimus) tetragonon (Herbst, 1790) ( Fig. 4 G), and the anterolateral margins are very short with weak dorsolateral margins in the U. (Gelasimus) vocans species complex (e.g. U. (Gelasimus) jocelynae Shih, Naruse & Ng, 2010 in Fig. 4 H).

Another character of Xeruca is having a major cheliped with straight cutting margins (i.e. the pollex’s lower and dactylus’s upper margins) more than half the length of the fingers, and the gape less than half the length of the fingers ( Fig. 5 A). This character is different from most other species with “forceps-like” fingers (cf. Crane 1975: figs. 38–41). Some subgenera however have such “scissor-like” fingers, but the distal cutting margins of the fingers are less than half the length of the fingers, and are slightly curved in most species, e.g. U. (Australuca) longidigitum (Kingsley, 1880) ( Fig. 5 B), U. (Australuca) bellator (White, 1847) ( Fig. 5 C), U. ( Uca ) princeps (Smith, 1870) ( Fig. 5 D), and U. (Afruca) tangeri (Eydoux, 1835) ( Crane 1975: fig. 45, pl. 18).

Some species of the subgenus Uca have conspicuous depth of the dactylus and pollex of the major cheliped, with longer and straight distal cutting margins in some individuals, e.g. U. ( Uca ) insignis (Milne-Edwards, 1852) (Bott 1954: pl. 14 (1 )), U. ( Uca ) maracoani ( Crane 1975: pl. 21 A–D), U. ( Uca ) monilifera ( Crane 1975: pl. 18 E– H), and U. ( Uca ) ornata ( Crane 1975: pl. 21 E–H). However, because the character of the deep fingers is peculiar, they can be easily separated from Xeruca and other species of fiddler crabs.

The handedness of Xeruca is close to a 1: 1 ratio ( Shih et al. 1999), which is consistent with the ratio of most species, but different from the mostly right-handed Gelasimus ( Barnwell 1982; Yamaguchi 1994).

The gastric mill (especially the urocardiac ossicles) had recently become an important character in crab systematics, from familial to specific levels (Yang 1986; Beinlich & von Hagen 2006; Sakai et al. 2006; Allardyce & Linton 2010; Naderloo et al. 2010). The urocardiac ossicles of Xeruca are of the simple form, i.e. fewer transverse ridges of median teeth, especially those on the posterior tooth plate ( Fig. 7). There are two transverse ridges of median teeth on the tooth plate, with additional weak and lower 2 to 3 cusps on the stem region, although this is not discernible on smaller individuals (e.g. CW 14.6 mm; Fig. 7 C). Both subgenera Afruca and Uca are also characterized by possessing two transverse ridges of median teeth on the tooth plate ( Fig. 8 A, B; Franklin Barnwell, personal communication). The number of transverse ridges on the tooth plate is variable for other subgenera ( Naderloo et al. 2010; unpublished data), but some species that also have similar simple forms, e.g., U. (Tubuca) acuta (Stimpson, 1858) ( Fig. 8 C) and U. (Austruca) lactea ( De Haan, 1835) ( Fig. 8 D). However, Xeruca can be distinguished from others by different shapes of ridges and the gaps not reaching to the central ridge, as well as variable numbers and shapes of cusps or transverse ridges on the stem region.

Although Crane (1975) placed U. formosensis under the same subgenus together with U. tetragonon and the U. vocans species complex, their urocardiac ossicles are totally different. Species of the subgenus Gelasimus have a unique setal structure on the lateral margins of the posterior stem region, with 4 to 5 transverse ridges on the tooth plate (e.g., U. (Gelasimus) tetragonon , Fig. 4 E; U. (G.) vocans (Linnaeus, 1758) , Fig. 4 F; unpublished data), which are not seen in Xeruca ( Fig. 7).

The G 1 of Xeruca ( Fig. 6) is similar to that of U. (Gelasimus) tetragonon and some members of Tubuca (e.g. U. (Tubuca) arcuata and the U. (Tubuca) dussumieri species complex) ( Crane 1975: figs. 61, 63A, B), but can be separated by the broad and thickened inner process, bent obliquely forward at right angles in Xeruca ( Fig. 6; Crane 1975: fig. 63 C).