Salmoneus secundus, Ashrafi & Ďuriš, 2025

Salmoneus secundus sp. nov.

( Figs. 5–8 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

Salmoneus cf. yoyo View in CoL — Ashrafi et al., 2025: 8, fig. 3B.

Material examined. Holotype: non-ovig. specimen (cl 3.6 mm), MNHN-IU-2013-11109 , fcn Vn07-40, Hon Chong Beach, N. of Nhatrang , Nhatrang Bay, Vietnam, 12°16.41’N 109°12.33’E, 29 Aug. 2007, depth 3 m, from burrow in sandy bottom, yabby pump; leg. Z. Ďuriš. GoogleMaps

Description. Carapace ( Fig. 5A–C View FIGURE 5 ) glabrous, smooth, without dorsal carina nor tubercle; frontal region concealing most of eyes in dorsal view and partly concealing them in lateral view; rostrum triangular in dorsal view, tapering distally into subacute tip reaching to about distal margin of second antennular article, slightly longer than broad, ventrally smooth; orbital teeth triangular, subacute, about twice as long as broad, reaching to approximately midlength of first antennular article; anterolateral suture present, pterygostomial angle broadly rounded, cardiac notch deep.

Pleon ( Fig. 5C, D View FIGURE 5 ) smooth; pleura of first to fifth pleonites rounded anteroventrally and posteroventrally; sixth pleuron with small triangular projection flanking each side of telson, posteroventral flap incomplete on right side and complete on left side.

Telson ( Fig. 5E View FIGURE 5 ) sub-rectangular, tapering distally, about six times as long as distal width, proximal margin about three times as broad as distal margin; dorsal surface with two pairs of spiniform setae located at about 0.6 and 0.8 telson length; posterior margin with minute central notch furnished with 2 setae, and two pairs of spiniform setae, mesial pair about twice as long as lateral one and about five times as long as spiniform setae on dorsal surface.

Antennule ( Fig. 5A, B View FIGURE 5 ) with peduncle relatively stout; first antennular article slightly longer than broad, stylocerite relatively slender, with subacute tip reaching to distal margin of second antennular article; second article slightly broader than long; third antennular article about 1.8 times as long as second one, 1.3 times as long as broad; lateral antennular flagellum biramous, fused portion with two subdivisions, shorter ramus well-developed, reaching to about fourth or fifth subdivision of longer ramus, with three groups of aesthetascs.

Antenna ( Fig. 5A, B View FIGURE 5 ) with stout basicerite, its distoventral margin armed with subacute tooth and minute blunt subdistal projection, superior margin subrounded; scaphocerite overreaching antennular peduncle, lateral margin almost straight, blade slightly surpassing lateral tooth; carpocerite stout, reaching to approximately midlength of third antennular article, flagellum not particularly stout.

Third maxilliped ( Fig. 7A View FIGURE 7 ) with coxa bearing strap-like epipod and somewhat broadly rounded lateral plate; antepenultimate article slender, about 5.4 times as long as proximal width, completely fused to ischium and basis, sutures not visible; penultimate article slender, about 0.4 times as long as antepenultimate article; ultimate article slender, tapering distally, about 1.7 times as long as penultimate article, distally armed with two small, subapical spiniform setae; exopod slender, slightly overreaching antepenultimate article; arthrobranch slightly hypertrophied, multilamellate.

First pereiopods ( Fig. 6 View FIGURE 6 ) subequal in size, but different in shape. Major cheliped ( Fig. 6A–C View FIGURE 6 ) robust, carried flexed under body when not in use; coxa with strap-like epipod and setobranch; basis short; ischium relatively slender proximally and widening toward distal margin, about twice as long as proximal width, armed with one small spiniform seta on ventrolateral margin; merus relatively slender, about 1.5 times as long as ischium, ventral margin slightly concave, ventromesial margin with three small tubercles distributed near midlength; carpus vase-shaped, about four times as long as proximal width; chela enlarged, slightly swollen, as long as basis to merus combined lengths; palm slightly swollen, relatively slender, about 2.4 times as long as wide, subcylindrical, ventral margin with four small tubercles located on distal half, slightly longer than fingers; fingers with strongly crossing fingertips, not gapping when closed, dactylus with cutting edge serrated with minute teeth on proximal two-thirds; pollex serrated with minute teeth on proximal two-thirds and one subdistal tooth. Subminor cheliped ( Fig. 6D–F View FIGURE 6 ) slightly more robust than major cheliped; coxa with strap-like epipod and setobranch; ischium relatively slender proximally and widening toward distal margin, about five times as long as proximal width, armed with one small spiniform seta on ventrolateral margin; merus relatively slender, about twice as long as ischium, ventral margin with shallow longitudinal concavity, ventromesial margin with four small tubercles distributed along midlength; carpus vase-shaped, about three times as long as proximal width; chela enlarged, stout, about 1.4 times as long as merus; palm moderately swollen, about three times as long as wide, subcylindrical, ventral margin with four small tubercles located on distal half, about 1.8 times as long as fingers; fingers stout, with strongly crossing fingertips, not gapping when closed, pollex with cutting edge armed with two strong subtriangular teeth, dactylus stout, strongly convex dorsally, cutting edge armed with two strong subtriangular teeth.

Second pereiopod ( Fig. 7B View FIGURE 7 ) moderately long, slender; coxa with strap-like epipod and setobranch; ischium slender, about four times as long as wide, armed with small spiniform seta on ventrolateral margin; merus slender, slightly longer than ischium, ventral margin slightly concave; carpus slender, 1.2 times as long as merus, with five subdivisions, proximal subdivision longest, subequal to sum of others, second to fourth subdivisions subequal, last subdivision slightly shorter than combination of second to fourth ones, chela about 0.5 times as long as carpus.

Third pereiopod ( Fig. 7C View FIGURE 7 ) moderately slender; coxa with strap-like epipod and setobranch; ischium slightly widening distally, about 3.7 times as long as widest part, with two small spiniform setae on ventrolateral surface; merus slightly inflated, about 1.3 times as long as ischium; carpus more slender and about 0.6 times as long as merus, 4.5 times as long as distal width, armed with small spiniform seta on distoventral margin; propodus slender, about 1.3 times as long as carpus, ventral margin with two single spiniform setae in addition to distal pair of spiniform setae flanking dactylar base and one spiniform seta on dorsodistal margin; dactylus simple, moderately slender, slightly curved, about 0.5 times as long as propodus. Fourth pereiopod ( Fig. 7D View FIGURE 7 ) generally similar to third one but slightly more slender; ischium armed with one spiniform seta on distoventral margin in addition to two spiniform setae on mid-ventro-lateral margin. Fifth pereiopod ( Fig. 7E View FIGURE 7 ) more or less similar to fourth pereiopod in length; coxa without strap-like epipod, with setobranch; merus slender, about 7.4 times as long as broad, twice as long as ischium; carpus lacking spiniform seta on distoventral margin; propodus bearing two small single spiniform setae on proximal half of ventral margin in addition to seven transverse rows of microserrulate setae on distal half of distoventral margin.

Uropods ( Fig. 5E View FIGURE 5 ) with lateral lobe of protopod broadly triangular; exopod ovate, anterolateral margin with small triangular tooth adjacent to slender spiniform seta, diaeresis sinuous; endopod slightly longer than exopod, ovoid, without specific feature.

Colour in life ( Fig. 8 View FIGURE 8 ). Body generally semi-transparent; carapace with dense red chromophores all over except for frontal region; rest of body semi-transparent.

Etymology. The species name is derived from the Latin word “secundus ,” meaning “second,” to emphasize that this is the second species in the genus Salmoneus in which the unique chelipeds bear a resemblance to those found in several species of Athanas Leach, 1814 ; used as a noun in apposition.

Type locality. Nhatrang Bay , Vietnam, South China Sea (present study).

Remarks. Salmoneus secundus sp. nov. is closely related to S. yoyo , another distinctive species within the genus. Both species are easily distinguishable from other Salmoneus species by their unique color patterns and the distinctive armament of their major and subminor chelipeds, i.e. tubercles on the ventromesial margin of the merus as well as the ventral margin of the palm (see Fig. 6 View FIGURE 6 ; and Anker et al., figs 2B, D, G, I). Salmoneus secundus sp. nov. differs from S. yoyo in several characters. Firstly, and more importantly, S. yoyo is characterized by a prominent hook-shaped projection on the distomesial margin of the merus of both the major and subminor chelipeds (Anker et al. 2016, fig 2B, D, E, G, I) which is absent in S. secundus sp. nov. Secondly, in S. secundus sp. nov., both fingers of the major cheliped are serrated with minuscule teeth on the proximal two-thirds, whereas S. yoyo bears prominent teeth on both fingers (Anker et al. 2016, fig 2A–C, F–H). Thirdly, the scaphocerite of S. secundus sp. nov. clearly overreaches the antennular peduncle, while in S. yoyo it extends only to the extremity of the antennular peduncle (Anker et al. 2016, fig. 1A, B).

A distinctive feature of S. secundus sp. nov. is the variation in the shape of the posteroventral flap of the sixth pleonite, which is incomplete on one side and complete on the other. With only a single specimen available, it is unclear whether this variation is typical of the species or represents a malformation. If the former, this species occupies a position intermediate of the genera Salmoneus Holthuis, 1955 , and Deioneus Dworschak, Anker, and Abed-Navandi, 2000 , based on this particular character. Anker (2020) reviewed the characters used by Dworschak et al. (2000) to differentiate Salmoneus and Deioneus and concluded that the presence of a complete articulated flap on the sixth pleuron is the only reliable character distinguishing Deioneus from Salmoneus . In the single available specimen of S. secundus sp. nov., the articulated flap exhibits both complete and incomplete states, reflecting characteristics of the both genera. This raises questions about the reliability of this character in generic level differentiation. However, given the uncertainty surrounding the flap’s true status in S. secundus sp. nov., and the fact that resolving the status of Deioneus is beyond the scope of this study, we defer this discussion to a future analysis.