Salmoneus ngae sp. nov., 2024

Anker, Arthur, 2024, On a new, burrow-associated species of Salmoneus Holthuis, 1955 (Decapoda: Alpheidae) from the Indo-West Pacific, Zootaxa 5476 (1), pp. 17-25 : 18-23

Salmoneus ngae sp. nov.

( Figs. 1–3 )

Salmoneus alpheophilus .— Anker et al. 2020: 323, figs. 16, 17.

Type material. Holotype: ovigerous specimen (cl 7.2 mm), MNHN-IU-2018-1019, New Caledonia, north-eastern coast, Pouébo , sta. KM607 , 20°17.6’S, 164°29.1’E, shallow subtidal sand flat with nearby patches of seagrass and fragmented coral rubble, depth 0.5–1 m, suction (yabby) pump, in burrow of Alpheus rapax [host deposited under MNHN-IU-2018-1010], leg. A. Anker, 19.09.2018 . Paratype: specimen with some unfertilised eggs (cl 6.6 mm), MNHN-IU-2018-1031, same collection data as for holotype.

Description. Small-sized alpheid shrimp, but relatively large-sized for Salmoneus . Carapace ( Fig. 1A, B ) covered by short erect setae; antero-lateral suture present; pterygostomial angle broadly rounded; cardiac notch deep. Rostrum ( Fig. 1A, B ) elongate triangular in dorsal view, slightly descendent in lateral view, almost twice as long as wide at base, acute distally; tip reaching or overreaching mid-length of second article of antennular peduncle; lateral margins slightly concave proximally; dorsal rostral carina distinct, extending posteriorly well beyond base of rostrum, ending in post-rostral tubercle; ventral carina with minute, acute or subacute, subdistal tooth. Orbital teeth ( Fig. 1A, B ) well developed, about 0.2 of rostrum length, subtriangular, acute distally, not extending beyond eyes.

Eyes ( Fig. 1A, B ) largely exposed dorsally and laterally, with only most proximal part of eyestalks concealed by base of rostrum and orbital teeth; cornea somewhat reduced, but normally pigmented; anterodorsal margin rounded, unarmed.

Pleon ( Fig. 1C ) patchily covered by erect setae; pleura of first to third pleonite rounded antero- and posteroventrally; fourth pleuron subacutely produced posteroventrally; fifth pleuron with posteroventral angle produced as small sharp tooth; sixth pleonite not particularly elongate, with acute subtriangular projection flanking telson on posterior margin and barely discernible suture near distally acute posteroventral angle; preanal plate broadly rounded.

Telson ( Fig. 1D, E ) moderately slender, subrectangular, tapering distally, about 2.5 times as long as proximal width; dorsal surface covered with erect setae and armed with two pairs of stout spiniform setae situated at about 0.5–0.55 and 0.75–0.8 telson length, respectively, posterior pair located closer to lateral margin than anterior pair; posterior margin with two pairs of elongate spiniform setae, mesial slightly longer than lateral, and deep U-shaped median notch, latter with two plumose setae.

Antennular peduncle ( Fig. 1A, B, F ) relatively stout; visible portion of first article as long as wide; stylocerite stout, broad, with acute or subacute tip, distinctly overreaching mid-length of second article; ventromesial carina with anteriorly directed, distally sharp tooth; second article somewhat elongate, about 1.8 times as long as wide; third article shortest, stout; lateral antennular flagellum with fused portion composed of three subdivisions; shorter free ramus with poorly demarcated subdivisions bearing about six groups of aesthetascs. Antenna ( Fig. 1A, B, G ) with basicerite very stout, armed with large, sharp tooth on distoventral margin; scaphocerite distinctively shorter than antennular peduncle; distolateral tooth strong, reaching well beyond anterior margin of blade, latter about 2.4 times as long as broad; carpocerite very stout, reaching well beyond half-length of scaphocerite and reaching middle of second article of antennular peduncle; flagellum long, somewhat thickened.

Mouthparts typical for genus. Third maxilliped ( Fig. 1H, I ) slender; coxa with strap-like epipod (mastigobranch) and prominent, rounded lateral plate; antepenultimate article about 2.7 times as long as penultimate article, with scattered setae on ventral and distodorsal margins; penultimate article four times as long as wide; ultimate article somewhat curved, tapering distally, with one apical and one subapical, short, spiniform setae; exopod well developed, however, not reaching end of antepenultimate article; arthrobranch well developed, but not particularly enlarged.

First pereiopods = chelipeds ( Fig. 2 ) very different in size, asymmetrical in shape. Major cheliped ( Fig. 2A–D ) robust, carried folded at rest; ischium unarmed ventrally; merus long, slender, distally widening, six times as long as distal height, slightly depressed ventrally; carpus cup-shaped, distally much wider, with several blunt lobes; chela moderately swollen, subcylindrical, longer than merus and ischium combined; palm about twice as long as maximal width, about 0.9 of merus length, smooth, with deep depression ventroproximally, without ripples ventrally; fingers about 0.7 length of palm, subequal in length, not gaping when closed, slightly twisted mesially; fingertips strongly curved, crossing subapically; cutting edges of pollex and dactylus with about 10 rounded-subtriangular, somewhat spaced teeth, proximal-most and distal-most smallest. Minor cheliped ( Fig. 2E, F ) much smaller and weaker than major cheliped, slender; ischium with small spiniform seta on ventrolateral surface; merus noticeably longer than ischium, somewhat convex dorsally, about 4.5 times as long as maximal width; carpus slender, subcylindrical, about 1.2 times as long as merus, widening distally; chela about 0.6 of carpus length; fingers slightly longer than palm, simple, with unarmed cutting edges.

Second pereiopod ( Fig. 1J ) slender; ischium elongate, about six times as long as wide, with one spiniform seta on ventrolateral surface, at about 0.4 of article length; merus long, almost 1.7 times as long as ischium; carpus slender, with five subarticles, first much longer than combined length of remaining four; approximate length ratio of carpal subarticles: 7.5: 1.5: 1: 1: 2.5. Third pereiopod ( Fig. 1K, L ) moderately slender; ischium elongate, about four times as long as wide, with three spiniform setae on ventrolateral surface; merus about 1.8 times as long as ischium, about 6.5 times as long as maximal width; carpus distinctly slenderer than merus, about 0.8 length of merus, distoventrally with small seta; propodus 0.9 length of carpus; ventral margin bearing armed with two widely spaced spiniform setae; distoventral margin adjacent to propodo-dactylar articulation with one pair of spiniform setae; dactylus slender, gently curved, simple, about 0.6 of propodus length. Fourth pereiopod ( Fig. 1M ) generally similar to third pereiopod, slightly shorter and slenderer. Fifth pereiopod ( Fig. 1N, O ) much slenderer than third and fourth pereiopods; ischium unarmed; merus about twice as long as ischium, almost seven times as long as wide; carpus slightly longer than merus, more than 8.5 times as long as wide; propodus about 1.2 times as long as carpus; ventromesial margin with three widely spaced, short spiniform setae; distoventral margin adjacent to propodo-dactylar articulation with one pair of long spiniform setae; propodal cleaning brush well developed, composed of numerous transverse rows of micro-serrulate setae extending from mid-length of article to its distal end; dactylus slender, simple, slightly shorter than half-length of propodus, otherwise similar to that of third and fourth pereiopods.

Second pleopod with appendices masculina and interna ( Fig. 1P ) subequal in length, not exceeding distal margin of endopod; appendix masculina furnished with slender spiniform setae along inner (mesial) margin and on apex. Uropod ( Fig. 1Q ) with lateral lobe of protopod distally produced as acute tooth; exopod moderately broad, ovate, with small distolateral tooth adjacent to stout spiniform seta; diaeresis sinuous, with blunt lateral projection adjacent to distolateral spiniform seta; endopod as long as exopod, slightly narrower, without diagnostic features.

Colour pattern. Holotype: body semi-opaque, whitish to pale yellow, patchily covered with red chromatophores; most numerous and most intensely red chromatophores present on carapace, except for frontal and postrostral areas and branchiostegial area adjacent to ventral margin; smaller chromatophores present on pleon, particularly on first, second, fourth and sixth pleonite, and telson, being denser on first, second and fourth pleonites, more scattered on sixth pleonite and telson; third article of antennular peduncle with conspicuous cluster of red chromatophores; rest of body and appendages, including major cheliped, whitish or whitish with yellow tinge; ovaries olive-green ( Fig. 3 ). Paratype: generally similar, but with chromatophores much less conspicuous, contracted.

Etymology. The new species is named after and in memory of the author’s colleague and friend, Ngan-Kee Ng, also for her significant contributions to systematics of brachyuran crabs.

Distribution. Presently known from the type locality on the north-eastern coast of New Caledonia (present study) and Lombok, Indonesia (Anker et al. 2015, as S. alpheophilus ; see below).

Ecology. The New Caledonian type locality of S. ngae sp. nov. is a shallow (0.5–1 m), near-shore sandflat with some seagrass patches and coral rubble, a few meters away from a fringing coral reef and its drop off into a deeper channel. Both specimens were collected from burrows of Alpheus rapax Fabricius, 1798 . In Lombok, several specimens of S. ngae sp. nov. were collected on a seagrass flat at low tide (Anker et al. 2015, under S. alpheophilus ).

Remarks. Salmoneus ngae sp. nov. is preliminarily assigned to the informal S. gracilipes Miya, 1972 group of Anker & Marin (2006), which considerably increased in number of species included and morphological diversity since its original definition ( Anker 2019b, 2022; Anker et al. 2020; Ashrafi et al. 2020, 2022). In fact, the S. gracilipes group is one of the most vaguely defined seven groups of Salmoneus established by Anker & Marin (2006) and certainly does not represent a monophyletic entity; however, it can still be used for purely taxonomic purposes. In the Indo-West Pacific, the following species are presently referred to the S. gracilipes group: S. tafaongae Banner & Banner, 1966 ; S. gracilipes Miya, 1972 ; S. colinorum De Grave, 2004 ; S. alpheophilus Anker & Marin, 2006 ; S. pusillus Anker & Marin, 2006 ; S. falcidactylus Anker & Marin, 2006 ; S. venustus Anker, 2019 ; S. ikaros Anker, Al-Kandari & De Grave, 2020 ; S. rashedi Ashrafi, Ďuriš & Naderloo, 2020 ; S. singularis Komai, Maenosono & Naruse, 2021 (tentatively); S. farasan Anker, 2022 ; and S. shojaei Ashrafi, Anker & Ďuriš, 2022 ( Banner & Banner 1966a; Miya 1972; De Grave 2004; Anker & Marin 2006; Anker 2019b, 2022; Anker et al. 2020; De Grave et al. 2020; Ashrafi et al. 2020, 2022; Komai et al. 2021). The only Atlantic species currently included in the S. gracilipes group are S. cavicolus Felder & Manning, 1986 and S. hispaniolensis Anker, 2010 ( Anker & Marin 2006; Anker 2010, 2020).

The presence of a strong mid-dorsal carina on the rostrum and post-rostral area of the carapace, and terminating posteriorly by a small but distinct tubercle, immediately separates S. ngae sp. nov. from most of the species listed above, viz. S. farasan , S. tafaongae , S. falcidactylus , S. venustus , S. shojaei , S. ikaros , S. hispaniolensis , S. pusillus , S. alpheophilus , the latter two species presenting a small post-rostral tubercle, but no mid-dorsal carina ( Anker & Marin 2006; Anker 2010, 2019b, 2022; Anker et al. 2020; De Grave et al. 2020; Ashrafi et al. 2022); S. gracilipes , S. colinorum and S. cavicolus , all three with a weak rostral carina, but without post-rostral tubercle ( Miya 1972; Felder & Manning 1986; De Grave 2004; Anker et al. 2020); S. rashedi , with a faint rostral carina (not extending beyond the rostrum) and a minute post-rostral tubercle ( Ashrafi et al. 2020); and S. singularis , with a weak rostral carina, no post-rostral tubercle, and two strong sharp teeth in post-orbital position, a unique feature within the genus ( Komai et al. 2021).

Based on the overall morphology, S. ngae sp. nov. appears to be closest to S. gracilipes , S. rashedi and, especially, S. alpheophilus . Nevertheless, the new species can be separated from S. gracilipes , S. rashedi and S. alpheophilus , in addition to the development of a strong rostral carina and post-rostral tubercle (see above), by the second article of the antennular peduncle 1.8 times longer than wide vs. as long as wide in S. gracilipes , S. rashedi and S. alpheophilus ; the distolateral tooth of the antennal scaphocerite prominent and reaching far beyond the distal margin of the blade vs. more moderate and not reaching beyond the distal margin of the blade in S. gracilipes , S. rashedi and S. alpheophilus ; and the less numerous teeth on the cutting edges of the major chela fingers, about 10 in S. ngae sp. nov. vs. at least 14 in S. gracilipes , S. rashedi and S. alpheophilus ; specifically, from S. rashedi by the shorter stylocerite, not reaching the distal margin of the second article of the antennular peduncle vs. overreaching this margin in S. rashedi ; and from S. alpheophilus by the unarmed ischium of the major cheliped (vs. armed with a spiniform seta in S. alpheophilus ) (cf. Fig. 1A , 2B, D ; Miya 1972; Anker & Marin 2006; Ashrafi et al. 2020). Furthermore, S. ngae sp. nov. differs from S. gracilipes , S. rashedi and S. alpheophilus by the diagnostic colour pattern (cf. Fig. 3 ; Anker & Marin 2006; Anker et al. 2020: figs. 6, 7; Ashrafi et al. 2020: fig. 4), although the identity of the material previously assigned to S. gracilipes (Anker et al. 2015, 2020) requires confirmation.

Along the same lines, the material from Lombok, Indonesia, identified as S. alpheophilus in Anker et al. (2015), is herein reidentified as S. ngae sp. nov., based on the presence of a strong mid-dorsal carina, the similar proportions of the second article of the antennular peduncle, and the striking colour pattern, which perfectly corresponds to that of the type specimens from New Caledonia, down to the distinctive red patch on the third article of the antennular peduncle (cf. Fig. 1 ; Anker et al. 2015: figs. 16, 17). Other material identified by the author as S. cf. alpheophilus or S. aff. alpheophilus (A. Anker, pers. obs.), but not yet reported, ranging from the Red Sea to Madagascar and French Polynesia, is currently under study.

Salmoneus ngae sp. nov. is the eighth species of Salmoneus reported to be associated with burrows of Alpheus spp. in various parts of the world and different habitats, the other seven species being S. carvachoi Anker, 2007 , S. malagensis Anker & Lazarus, 2015 , S. rostratus Barnard, 1962 , S. spiridonovi Marin, 2021 , and the abovementioned S. alpheophilus , S. shojaei and S. colinorum ( Anker 2003a; De Grave 2004; Anker & Marin 2006; Anker 2007; Anker & Lazarus 2015; Marin 2021; Ashrafi et al. 2022). In addition, S. bruni Banner & Banner, 1966 , S. singaporensis Anker, 2003 , and S. aduncus Komai, 2022 , which are clearly related to S. rostratus (cf. Banner & Banner 1966b; Anker 2003a; Komai 2002), may reveal as further “inquilines” of burrowing snapping shrimps in the future.

Figures

FIGURE 1. Salmoneus ngae sp. nov., holotype, ovigerous specimen (cl 7.2 mm) from Pouébo, New Caledonia, MNHN-IU- 2018-1019:A, frontal region, dorsal; B, same, lateral; C, posterior pleonites, lateral; D, telson, dorsal; E, same, posterior margin, dorsal; F, ventromesial tooth of first article of antennular peduncle (drawn without scale); G, antennal scaphocerite, dorsal; H, third maxilliped, lateral; I, same, detail of distal part of ultimate article, dorsomesial; J, second pereiopod, lateral; K, third pereiopod, lateral; L, same, dactylus, lateral; M, fourth pereiopod, lateral; N, fifth pereiopod, lateral; O, same, propodus and dactylus, mesial; P, appendices masculina and interna of second pleopod, anterior; Q, uropod, dorsal.

FIGURE 2. Salmoneus ngae sp. nov., holotype, ovigerous specimen (cl 7.2 mm) from Pouébo, New Caledonia, MNHN-IU- 2018-1019: A, major (right) cheliped, mesial; B, same, lateral; C, same, carpus and chela, ventromesial; D, same, chela with fingers open, ventrolateral; E, minor (left) cheliped, lateral; F, same, chela, lateral.

FIGURE 3. Salmoneus ngae sp. nov., holotype, ovigerous specimen (cl 7.2 mm) from Pouébo, New Caledonia, MNHN-IU- 2018-1019: A, shrimp in life, dorsal; B, same, lateral. Photographs by the author.