Tritodynamia serratipes Anker & Ng, 2014, sp. nov.
Creators: name: Anker, Arthur
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Macrophthalmidae
Tritodynamia
Tritodynamia serratipes

description: Tritodynamia serratipes sp. nov.
(Figs. 1–3)
Type material. Holotype, female (CW 8.2 mm, CL 4.5 mm), ZRC 2014.0229, field collection number 5317 DR1- AA-37, Singapore, Straits of Singapore, off Marina East, 1º17'199"–1º17'185" N 103º53' 830"–103º53'575" E, 6.3–6.5 m, soft mud, rectangular dredge, R.V. Galaxea, coll. C.K. Chim, S.C. Lim, A. Anker, H.P.S. Wong, 26 March 2014.
Comparative material. Tritodynamia horvathi Nobili, 1905: 2 males (CW 12.5 mm, CL 7.7 mm; CW 12.6 mm, CL 8.2 mm), 1 female (CW 13.3 mm, CL 9.0 mm), ZRC 1970.1.21.20–22, Japan, coll. T. Sakai, 1967. Tritodynamia yeoi Naruse & Ng, 2010: holotype, male, CW 7.1 mm, CL 3.5 mm, ZRC 2006.0081, Singapore, Pulau Ubin, Chek Jawa, intertidal flats, coll. K.L. Yeo, 21 August 2001.
Diagnosis. Carapace transversely elongated, CW / CL ratio about 1.8; front about 0.2 times CW, margin entire, cristate, about 0.4 times width between external orbital angles; anterolateral margin cristate. Mxp3 with ischium slightly shorter than merus; propodus with projecting, foliaceous, distodorsal lobe; dactylus elongate-elliptical, inserted at ventral submedian part of propodus, reaching far beyond propodus. P1 symmetrical; lower part of manus with 2 granulated cristae, lower crista of manus with deep concavity on subventral inner face adjacent to pollex base; cutting edge of pollex with 2 strong teeth in proximal third, proximal tooth subtriangular, distal tooth subquadrate; dactylus with 2 strong teeth in proximal half, proximal tooth subtriangular, distal tooth subquadrate. P2 with merus about 2.8 times as long as wide, with row of granules distally on anterodorsal surface, numerous granules on posterior surface, including lines of strong granules along posterodorsal, posteroventral margins. P3 elongated, length from merus to dactylus about 1.7 times CW; ischium with granules on dorsal, ventral surfaces; posterior margin with strong projecting tooth; merus with anterior, posterior surfaces bearing numerous rounded, conical granules; posterodorsal, posteroventral margins lined with strong conical granules; propodus about 1.4 times as long as dactylus, 1.9 times as long as wide; lines of strong granules present on anterior, posteroventral margin, midline of dorsal surface; posterodorsal margin with uneven row of conical or slightly arched, usually adjacent teeth, at least 7 of them conspicuously strong. P4 merus stout, about 2.2 times as long as wide, anterior, posterior surfaces with numerous granules, especially on posterodorsal, posteroventral margins; propodus about 1.3 times as long as dactylus, about 2.2 times as long as wide, without granules. P5 with dactylus directed slightly dorsally. First, second thoracic sternites forming subtriangular structure, medially depressed, separated from third sternite by deeply concave suture.
Description. Carapace elliptical, transversely elongated, CW / CL ratio about 1.8; dorsal surface slightly convex longitudinally, glabrous, sparsely punctate (Figs. 1 A, 3A). Front slightly directed downwards, about 0.2 times CW, not reaching noticeably beyond external orbital angles, with shallow anteromedian depression; frontal margin entire, cristate, straight, about 0.4 times of width between external orbital angles; supraorbital margin sinuous, cristate, with slight notch on mesial angle; infra-orbital margin present only on external third, composed of row of small granules; suborbital crista lined with small granules; inner orbital tooth large; external orbital angle approximately right-angled, directed anteriorly, ventral surface gently swollen, margin confluent with anterolateral margin (Figs. 1 A, B, 3C). Anterolateral margin cristate, lined with conspicuous granules, margin evenly convex posterior to external orbital angle; posterolateral margin cristate, lined with small granules, converging posteriorly; posterolateral region clearly demarcated from dorsal surface by sinuous line of granules; posterior carapace margin wide, slightly convex (Figs. 1 A, 3A). Posterior margin of epistome with broad median triangular structure, lateral margins gently concave (Figs. 1 C, 3C).
Eyestalk with well-developed cornea, subdistal width of cornea slightly narrower than maximum width of peduncle in frontal view (Figs. 1 A, B, 3C). Antennular fossa subglobular (Fig. 3 C). Antennules typical for genus (Fig. 1 D). Antennae short, flagellum as long as width of orbit (Fig. 1 B). Third maxilliped (Mxp3) weakly operculate, resulting in large median opening between closed right, left maxillipeds; ischium slightly shorter than merus, ventral surface with longitudinal depression along mesial margin, latter strongly convex, finely toothed, with numerous long setae; merus slightly widening distally, with shallow longitudinal groove along mesial margin, latter finely toothed, distal 2 teeth strongest, separate from others, with numerous long setae; carpus widening distally, ventral margin unarmed, setose; propodus with projecting, foliaceous, distodorsal lobe, latter distally rounded, with long setae reaching or overreaching setae of distal margin of dactylus, dorsomesial surface of foliaceous lobe with shorter, dense setae; dactylus inserted at ventral submedian part of propodus, elongateelliptical, reaching far beyond foliaceous lobe of propodus, fringed with long setae on margins, just reaching first, second thoracic sternites (Figs. 1 E, 3C).
Chelipeds (P1) symmetrical, equal in size, similar in shape; merus with distodorsal margin lined with granules; carpus somewhat swollen, rhomboidal, with distodorsal projection, strong external dorsolateral angle having some subconical granules, internal surface with row of spaced granules; manus generally smooth, with convex external surface, only slightly convex internal surface; dorsal surface with line of granules; external surface with faint carina in dorsal portion, 2 grooves in ventral portion, both continuing to pollex, bordered by low cristae lined with granules, lower crista as far as deep concavity adjacent to base of pollex, upper crista lined with granules throughout, with less individual granules on pollex; fingers somewhat gaping when closed; cutting edge of pollex with 2 strong teeth in proximal third, proximal tooth subtriangular, distal tooth subquadrate, teeth separated by moderate hiatus, with 10 or 11 smaller triangular or subtriangular-rounded teeth extending from 0.4 to 0.9 length of cutting edge, most distal teeth small; dactylus with 2 strong teeth in proximal half, proximal tooth subtriangular, distal tooth subquadrate, teeth separated by broad hiatus, with 6 or 7 smaller triangular or subtriangular-rounded teeth, extending from about 0.5 to 0.9 length of cutting edge; finger tips corneous, slender, pointed (Figs. 1 F–H, 2A, 3C).
Ambulatory legs (P2–5) relatively stout, especially P3, P4, setose; P3 longest, P5 shortest; combined length of merus to dactylus of P5 shorter than length of merus of P3 (Fig. 3 A). P2 with merus about 2.8 times as long as wide, with row of granules expanding distally on anterodorsal surface, numerous granules on posterior surface, including rows of strong granules along posterodorsal, posteroventral margins; dactylus tapering, with dense brush of setae (Figs. 1 I, 3A). P3 with combined length of merus to dactylus about 1.7 times CW; ischium with granules on dorsal, ventral surfaces, posterior margin with very strong, projecting tooth; merus stout, about 2.6 times as long as wide, subrectangular in cross-section, anterior, posterior surfaces with numerous rounded, conical granules, posterodorsal, posteroventral margins lined with particularly strong conical granules, some tooth-like; propodus about 1.4 times as long as dactylus, slightly tapering distally, 1.9 times as long as wide; anterior, posteroventral margin, midline of dorsal surface with lines of strong granules, posterodorsal margin with uneven row of conical or slightly arched, usually adjacent teeth, at least 7 of them conspicuously strong, including 4 strongest in proximal half; dactylus tapering, subspatulate, smoothly curving distally (Figs. 1 J, K, 3A, B). P4 significantly shorter than P2, fringed with numerous long plumose setae; ischium without projecting tooth on posterior margin; merus stout, about 2.2 times as long as wide, subrectangular in cross-section, anterior, posterior surfaces with numerous rounded or subconical granules, especially on posterodorsal, posteroventral margins; propodus about 1.3 times as long as dactylus, with convex margins, tapering distally, about 2.2 times as long as wide, without granules; dactylus slender, tapering, not curving (Figs. 1 L, 3A). P5 shortest, most slender, fringed with numerous long plumose setae; merus about 3.3 times as long as wide; posterodorsal, posteroventral margins with row of small granules; propodus oval-shaped, shorter than dactylus, smooth; dactylus slender, tapering, directed slightly dorsally (Figs. 1 M, 3A).
Thoracic sternum broad; first, second sternites completely fused, forming subtriangular structure, medially depressed, appearing sunken; separated from third sternite by prominent deeply concave suture; third, fourth sternites fused, with only parts of median suture discernible as ridge of small granules; third sternite with surface covered with small, rounded to flattened granules, lateral margin faintly granular; fourth sternite with lateral margin lined with small granules (Figs. 1 C, 2A); vestigial abdominal locking mechanism present as granule on anterior half of sixth sternite, adjacent to suture between fifth, sixth sternites; vulvae situated on anterior edge of sixth sternite, adjacent to suture between fifth, six sternites; each vulva subovate, with raised lateral margin, forming distinct, lip-like, sternal cover (Fig. 2 A, B).
Female abdomen covering most of thoracic sternum; all abdominal somites, telson free; abdominal somites with slightly convex lateral margins; first, second somites longitudinally narrow, subrectangular, separated from coxae of P5 by wide, subrectangular, thoracic eighth sternite; sixth somite with distal concavity accommodating telson; telson broadly triangular, distally rounded, greatest width about 1.5 times of median length (Figs. 2 B, 3B).
Colour pattern. Carapace brownish marbled with pale-yellow patches of irregular shape and various sizes, three largest and most conspicuous patches on branchial region near lateral and posterolateral margins, two transverse pale yellow lines present near cardiac region; cheliped merus and carpus pale brown with large white areas, chela mostly white; P2 and P5 mostly whitish with some pale brown markings, mainly on merus; P3 and P4 with more intense brownish background colour, with numerous rounded pale-yellow patches on merus or longitudinal pale yellow band on propodus, many shorter stiff setae (e.g., on carpus and propodus of P3) conspicuously dark tan-brown; abdomen and sternum white; cornea silvery (Fig. 3 A–C).
Type locality. Singapore, Straits of Singapore, off Marina East.
Distribution. Presently known only from the type locality in Singapore.
Etymology. In reference to the conspicuously serrated propodi of the second ambulatory legs (P3), the most obvious diagnostic feature of the new species.
Ecology. The holotype was dredged from a depth of 6.3–6.5 m, a few hundred meters from the coast; the bottom consisted of fine mud with some shell debris.
Remarks. Tritodynamia serratipes sp. nov. is one of the most distinctive members of Tritodynamia, differing from all the other species currently retained in the genus (Yang & Tang 2005; Naruse & Ng 2010) by its heavily serrated P3 propodus, having an uneven row of strong teeth along the posterodorsal margin (Figs. 1 J, K, 3A). The posterodorsal margin of P3 is smooth or minutely, at most moderately serrated, in all other species of Tritodynamia (e.g., Nobili 1905; Shen 1932, 1935; Sakai 1934, 1976; Chen 1979; Dai et al. 1980; Yang & Sun 1996; Yang & Tang 2005; Naruse & Ng 2010). In species with a moderately serrated posterodorsal margin of P3, the teeth are small and their number ranges from about 18–20 in T. japonica and T. bidentata to 23 or so in T. horvathi (Nobili 1905; Yang & Tang 2005). In contrast, these teeth are very strong in T. serratipes sp. nov., being conspicuous even in the general habitus view (Fig. 3 A), and their number does not exceed 15 (Fig. 1 J).
Another important feature of T. serratipes sp. nov. is the presence of 2 strong teeth in the proximal half of the cutting edge of the cheliped pollex (Figs. 1 F, 3C). This feature is shared only with T. fujianensis, which, however, differs from the new species by the frontal margin of the carapace being slightly emarginated (cf. Chen 1979: pl. 1, fig. 1) in contrast to straight in T. serratipes sp. nov. (Fig. 1 A). In addition, in T. fujianensis, the P3 propodus is unarmed posterodorsally (cf. Chen 1979: pl. 1, fig. 7) in contrast to the heavily serrated one in T. serratipes sp. nov. (Figs. 1 J, 3A), and the third maxilliped has a longer and narrower dactylus (cf. Chen 1979: pl. 1, fig. 2) compared to the relatively shorter dactylus in T. serratipes sp. nov. (Fig. 1 E).
In the remaining species of Tritodynamia, the cutting edge of the cheliped pollex is evenly (sometimes minutely) or irregularly serrated or has only 1 strong proximal tooth, sometimes followed by a distal serration (e.g., Nobili 1905; Sakai 1976; Dai et al. 1980; Dai & Yang 1991; Otani & Takahashi 1996; Yang & Sun 1996; Yang & Tang 2005; Naruse & Ng 2010). The armature of the cheliped fingers nevertheless has to be used with some caution for it was shown to be ontogenetically variable in T. horvathi, with 2 teeth on the dactylus in some younger crabs (form described as T. intermedia) and 1 tooth in the adults (Otani & Takahashi 1996).
Tritodynamia serratipes sp. nov. can be easily separated from the long-legged species T. longipropodum, T. dilatatum and T. yeoi by the much lower length-width ratio of the P3 propodus (cf. Dai et al. 1980; Yang & Sun 1996; Naruse & Ng 2010), and from T. horvathi, which has a more quadrate carapace, with CW / CL about 1.4 (cf. Nobili 1905: pl. X, fig. 1; Shen 1932: fig. 71) vs. 1.8 in T. serratipes sp. nov. (Figs. 1 A, 3A).
Tritodynamia serratipes sp. nov. represents the second record of Tritodynamia in tropical Asia. It is also the second species, together with T. yeoi, currently known from only a single specimen collected in Singapore. Both T. serratipes sp. nov. and T. yeoi are likely to be found elsewhere in the Sunda Shelf and perhaps beyond after more thorough collecting in muddy intertidal and shallow subtidal habitats. The apparent rarity of Tritodynamia spp. is probably mainly due to their cryptic lifestyle, i.e. dwelling in burrows of other invertebrates.
Johnson (1963: table I) reported as “ Tritodynamea sp.” (under Pinnotheridae) a crab associated with sipunculans in Singapore. As Johnson’s material could not be traced in the ZRC, this crab cannot be confirmed as a species of Tritodynamia. However, Johnson’s record provides a possible, albeit unconfirmed link to burrowing sipunculans, which are known as hosts for several pinnotherid crabs (Manning & Morton 1987; Morton 1988; Rahayu & Ng 2010).
description: Published as part of Anker, Arthur & Ng, Peter K. L., 2014, Tritodynamia serratipes sp. nov., a new marine crab from Singapore (Crustacea: Decapoda: Brachyura: Macrophthalmidae), pp. 369-376 in Zootaxa 3826 (2) on pages 370-375, DOI: 10.11646/zootaxa.3826.2.6, http://zenodo.org/record/225306