Richalpheus laeuadigitus Komai & Koreeda 2022, n. sp.
Creators: name: Komai, Tomoyuki
name: Koreeda, Reo
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Richalpheus
Richalpheus laeuadigitus

description: Richalpheus laeuadigitus n. sp.
[New Japanese name: Usubeni-ana-yadori-teppou-ebi]]
(Figs. 1–5, 6B)
Material examined. Holotype. KAUM-AT-1005, female (cl 10.5 mm), Kiire, Kagoshima Prefecture, Kyushu, Japan, 31°22.33’N, 130°32.50’E, 0.2 m deep at low tide, 9 May 2020, yabby pump, coll. R. Koreeda.
Paratypes. Collection data same as holotype: KAUM-AT 902, 1 female (cl 7.4 mm); KAUM-AT 920, 1 female (8.2 mm); KAUM-AT 921, 1 female (cl 8.2 mm), DNA voucher (LC 683777); KAUM-AT 922, 1 female (cl 5.3 mm); KAUM-AT 923, 1 male (cl 5.7 mm). KAUM-AT 1202, 1 male (cl 6.9 mm), Kiire, 31°22.35’N, 130°32.58’E, 21 June 2020, yabby pump, coll. Naoto Shimizu; KAUM-AT 1203, 1 female (cl 7.3 mm), same data. KAUM-AT 1490, 1 female (cl 6.9 mm), river mouth of Matsuzaki River, Shinjo, Tarumizu, Kagoshima Prefecture, 31°26.32’N, 130°44.11’E, tidal flat, 22 August 2021, coll. Naoto Shimizu. KAUM-AT 1352, 1 female (cl 4.5 mm), river mouth of Ogawa River, Minamiohsumi, Kimotsuki, Kagoshima Prefecture, 31°13.10’N, 130°45.42’E, tidal flat, 1 April 2021, yabby pump, coll. R. Koreeda, DNA voucher (LC 683778).
Diagnosis. Telson (Fig. 2D) 1.9–2.0 times as long as wide. Antennular peduncle (Fig. 2E, F) elongate, with article 2 more than twice as long as wide, article 1 with ventromesial carina bearing acute tooth; tip of antennular stylocerite reaching 0.6 of peduncular article 1. Major chela (4A–D; 5B) with dactylus relatively stout, with bulgelike ridge on occlusal margin; pollex with longitudinal groove in proximal 0.7 of occlusal margin. Posterior flap of uropodal exopod (Fig. 2J) less developed, with distolateral margin truncate or shallowly concave.
Description. Holotype female. Body (Figs. 1; 2A, B) somewhat compressed laterally.
Carapace (Fig. 2A, E, F) smooth, becoming deep posteriorly, subequal in length to anterior 3 pleomeres combined; frontal margin broadly rounded, deflexed in lateral view, without clearly defined rostrum or orbital teeth; anterolateral margin rounded, extending as far as frontal margin; ventrolateral area of branchiostegite membranous, with rounded notch at base of pereopod 1 (cheliped); cardiac notch deep, slit-like.
Pleon (Fig. 2B, C) elongate, pleomeres 1 and 2 combined subequal in length to pleomeres 3–5 combined, pleomere 2 longest; pleuron 2 slightly asymmetrical with posterior margin more produced than anterior margin; pleura 4 and 5 rounded posteroventrally. Pleomere 6 with clearly demarcated posteroventral plate. Telson (Fig. 2D) widest in proximal fifth, 1.9 times as long as wide, tapering to rounded posterior margin; dorsal surface with 2 pairs of spiniform setae inserted in deep pits, each spiniform seta slightly more than 0.1 times of telson length, first pair closer to lateral margin, located at 0.3 of telson length, second pair at some more distantly from lateral margin, located at 0.6 of telson length; posterior margin with 2 pairs of spiniform setae at posterolateral angles, lateral pair minute, mesial pair 0.2 times of telson length; anal tubercles feebly developed.
Eyes (Fig. 2E, F) completely concealed in dorsal and lateral views, partly visible in frontal view; anteromesial margin of eyestalks rounded; corneas relatively small, but well pigmented.
Antennular peduncles (Fig. 2E, F) elongate, 0.6 times as long as carapace, moderately stout, slightly flattened dorsoventrally, overreaching distal margin of antennal scaphocerite by length of peduncular article 3. Article 1 dorsomesial margin bearing short row of 5 (left) or 6 (right) minute spiniform setae in proximal half; stylocerite pressed against peduncle, tip free-standing, acutely pointed, reaching beyond 0.6 of article 1; ventromesial carina with sharp tooth directed anteriorly. Article 2 more than twice as long as wide, subequal in length to visible part of article 1. Article 3 about half-length of article 2. Lateral flagellum with shorter ramus carrying tufts of aesthetascs.
Antennal peduncle (Fig. 2E, F) with basicerite moderately stout, with relatively large ventrolateral distal spine. Scaphocerite ovate with lateral margin gently convex, 0.3 times as long as carapace, 1.9 times as long as wide, bearing small blunt distolateral tooth reaching beyond distal margin of subtruncate blade. Carpocerite reaching well beyond scaphocerite, but not reaching distal end of antennular peduncle.
Epistomal sclerite unarmed.
Mouthparts typical for genus on external observation. Maxilliped 3 endopod (Fig. 3A, B) falling slightly short of distal margin of article 2 of antennular peduncle; coxal lateral plate (Fig. 5A) developed into thick, distally tapering projection; antepenultimate article (basis-ischium-merus fused) strongly flattened, gently sinuous in dorsal view; penultimate and ultimate article much more slender than antepenultimate article, ultimate article gradually tapering to subacute apex, 1.3 times as long as penultimate article; mesial face of penultimate article sparsely setose, that of ultimate article having several transverse tracts of grooming setae; exopod (Fig. 3A, B) long, but not reaching distal margin of antepenultimate article; arthrobranch large.
Chelipeds (pereopods 1) greatly unequal and dissimilar. Major (left) cheliped (Figs. 4A–D; 5B) elongate, chela folded against merus when not in use, overreaching distal margin of scaphocerite by full length of chela when extended. Basis with subtriangular, plate-like projection on distolateral margin. Ischium very short, unarmed, articulation to merus strongly oblique. Merus slender, widened distally in dorsal view, fairly depressed dorsoventrally, gently arcuate in lateral view; ventrolateral margin ending in rounded distal tooth; dorsal surface rounded, distally upturned; ventral surface shallowly excavate. Carpus very short, cup-shaped; dorsal surface strongly constricted near base. Chela stout, subequal in length to carapace, 3 times as long as wide. Palm 1.8 times as long as wide; dorsal face generally smooth, rounded transversely, with deep transverse constriction near articulation with dactylus; ventral face with shallow, broad longitudinal groove along midline, fitting ventral face of merus when chela carried folded; fingers somewhat twisted, gaping when closed, tips touching, but not strongly crossing. Pollex strongly deflexed at distal to base, distal part strongly hooked, terminating in blunt apex; occlusal margin of dactylus longitudinally grooved, flanked by generally convex ridges. Dactylus noticeably curved, terminating in blunt apex; upper surface carinate along extensor margin; occlusal margin with bulge-like ridge along proximal 0.7, terminating distally in blunt point, fitting to groove on pollex, distal 0.3 of occlusal margin unarmed.
Minor (right) cheliped (Figs. 3C; 5C, D) slender, chela folded against merus when not in use, overreaching distal margin of scaphocerite by length of dactylus. Ischium unarmed, short, articulation to merus strongly oblique. Merus dorsoventrally flattened, only slightly arcuate, unarmed. Carpus very short, cup-shaped. Chela slender, 0.6 times as long as carapace, slightly longer than merus; palm smooth, ventral (flexor) surface somewhat inflated; fingers about 1.6 times longer than palm, slender, tips crossing. Pollex gently bowed, distal part strongly hooked, terminating in acute tip; occlusal margin with row of minute, barb-like teeth in proximal half, unarmed in distal half. Dactylus gently curved, terminating in acute tip; occlusal margin armed with row of minute, barb-like teeth also in proximal half.
Pereopod 2 (Fig. 3D) overreaching distal end of antennal carpocerite by length of chela. Ischium about 0.7 length of merus, unarmed. Merus subequal on length to carpus. Carpus divided into 4 segments, segment length ratio approximately equal to 4.5: 1.2: 1.0: 2.0. Chela 0.4 times as long as carpus, tapering distally, with brush-like tuft of setae on distal half of palm to pollex. Dactylus 0.7 times as long as palm.
Pereopod 3 (Fig. 3E) strongly compressed. Ischium short, unarmed. Merus with convex dorsal and ventral margins, 3.5 times as long as greatest width. Carpus short, less than half-length of merus, with prominent distoventral spiniform seta. Propodus narrowing distally, armed with 2 widely spaced, strong spiniform setae on flexor margin; flexor distal angle with 2 unequal spiniform setae (mesial seta stronger than lateral seta). Dactylus (Fig. 5F) 0.5 length of propodus, slightly curved mesially, subspatulate with subacute tip; flexor surface flat.
Pereopod 4 (Fig. 3F; 5G) generally similar to pereopod 3, but slightly shorter.
Pereopod 5 (Fig. 3G) shorter and more slender than pereopods 3 and 4. Propodus 1.3 times as long as carpus, with grooming apparatus consisting of 4 transverse rows of stiff setae in distal 0.2, otherwise unarmed. Dactylus (Fig. 5H) short, about 0.2 times as long as propodus, subconical, with flat flexor surface.
Gill formula including 5 pleurobranchs above pereopods 1–5, 1 arthrobranch above maxilliped 3, 2 lobe-like epipods (maxillipeds 1 and 2), no strap-like epipods on maxilliped 3 and pereopods 1–5, no setobranchs.
Pleopod protopods (Fig. 5I, J) each with thick ovigerous setae on mesial margin. Pleopod 1 (Fig. 5I) endopod small, about half-length of exopod, tapering distally, bearing numerous setae distally. Pleopod 2 (Fig. 5J) endopod subequal in length to exopod, with long, slender appendix interna (about half length of endopod) arising at proximal 0.4 of mesial margin.
Uropod (Fig. 2J) with protopod having broadly rounded lateral lobe and 1 small medial spine dorsally at articulation to endopod. Exopod with posterior flap very short, posterior margin roundly truncate, without incision or concavity; lateral margin slightly convex; diaeresis with feebly marked, broadly triangular tooth just lateral to posterolateral spiniform seta, and two much larger triangular teeth defined by similarly deep incisions. Endopod slightly longer than exopod, oval.
Paratypes. Generally similar to holotype. Telson 1.9–2.0 times as long as wide. Antennular peduncle article 1 with row of 5–6 minute spiniform setae on proximal half of dorsomesial margin. Antennal scaphocerite with distolateral tooth varying from sharply triangular (Fig. 5K) to blunt as in holotype. Male pleopod 1 with endopod (Fig. 5L) small (length less than half of exopod), bearing sparse setae. Male pleopod 2 with appendices masculina and interna (Fig. 5M) arising proximal to mid-length of endopod mesial margin; appendix masculina rod-like, distinctly shorter than appendix interna, bearing 1 stiff apical seta. Posterolateral margin of uropodal exopod distal flap truncate or slightly concave.
Colouration in life. Body and appendages (Fig. 1A–C) generally pale pink or pale orange semi-transparent, with numerous scattered red chromatophores on carapace, pleon, telson, antennae and major cheliped, occasionally forming intense tinge; pereopods 2–5 semi-transparent.
Distribution. Presently known only from three locations in Kagoshima Prefecture, Kyushu, Japan, i.e., Kiire (type locality), Tarumizu and Kimotsuki; lower intertidal.
Ecology. Eight specimens from Kiire, including the holotype female, were all collected from tidal flat consisting of soft mud, where there is a spring of fresh-water; scattered burrow openings were seen on the bottom surface (Fig. 6A). Sampling made on 9 May 2020 with the yabby pump yielded individuals of a large ptychoderid worm Balanoglossus misakiensis Kuwano, 1902, along with six individuals of the present new species (KAUM-AT 902, 920–923, and 1005), individuals of three callianassid ghost shrimp Neotrypaea harmandi (Bouvier, 1901), N. japonica (Ortmann, 1891) and Paratrypaea bouvieri (Nobili, 1904), and individuals of a pinnotherid crab Pinnixa balanoglossana Sakai, 1934, from those burrow openings (Fig. 6B). The other two specimens collected at Kiire by another occasion (21 June 2020; KAUM-AT 1202, 1203) were extracted from sediments together with specimens of Alpheus brevicristatus de Haan, 1844, but the collection field was also inhabited by Balanoglossus misakiensis. It is possible that the new species is commensal with one of those infaunal animals except for Pinnixa balanoglossana that is commensal with B. misakiensis (cf. T. Sakai 1934, 1976; K. Sakai 2002; Shimetsugu & Kimura 2018), though it is not easy to specify at present what is the host of R. laeuadigitus n. sp. The specimens from a tidal flat at the river mouth of Matsuzaki River, Tarumizu (KAUM-AT 1490) and from a tidal flat at the river mouth of Ogawa River, Kimotsuki (KAUM-AT 1352) were extracted from mud substrate also by using yabby pump, but no other invertebrates were found. Other species of Richalpheus species are also supposed to be associated with other infaunal invertebrates, possibly callianassid ghost shrimp, but not positively identified yet (Anker 2011).
Remarks. The configuration of fingers of the major cheliped provides diagnostic characters for species differentiation in Richalpheus (Anker 2011). In this regard, the present new species is most similar to R. palmeri. In R. laeuadigitus n. sp. and R. palmeri, the dactylus has a broad bulge-like ridge, occupying proximal half or more of the dactylar occlusal margin and fitting into a deep longitudinal groove on the pollex (Figs. 4E, D, 5B; see also Anker & Jeng 2006: fig. 4). In R. alpheoides, the dactylus has a well-defined, distally excavated tooth, situated in the proximal half of the dactylar occlusal margin, and fitting into a deep rounded fossa on the pollex (cf. Anker 2011: fig. 2D–F). In R. dahabensis, the dactylus has neither a bulge nor a tooth, whereas the pollex has a proximal groove (Anker & Dworschak 2007: fig. 3A). Richalpheus laeuadigitus n. sp. differs from R. palmeri in the following particulars: the telson is relatively wider in the new species than in R. palmeri (twice or less than twice as long as wide versus twice or more; Fig. 2D versus Anker & Jeng 2006: fig. 2k); the antennular stylocerite reaches to the 0.6 of the basal peduncular article in R. laeuadigitus n. sp. (Fig. 2F), rather than reaching to the 0.8 in R. palmeri (cf. Anker & Jeng 2006: fig. 2c); the uropodal diaeresis has two similarly deep incisions in R. laeuadigitus n. sp. (Fig. 2J), whereas it has a very shallow lateral incision and a deep mesial incision in R. palmeri (cf. Anker & Jeng 2006: fig. 2j).
Other than the characters of the major cheliped fingers, R. laeuadigitus n. sp. is very similar to R. dahabensis. Nevertheless, the following subtle differences might be diagnostic for discrimination between the two taxa: the telson is relatively wider in R. laeuadigitus n. sp. than in R. dahabensis (1.9–2.0 times as long as wide versus 2.3 times as long); the exopod of the maxilliped 3 does not reach the distal margin of the endopod antepenultimate article in R. laeuadigitus n. sp. (Fig. 3A, B), rather than overreaching it in R. dahabensis (cf. Anker & Dworschak 2007: fig. 2F).
Richalpheus alpheoides further differs from the new species, R. dahabensis and R. palmeri in the less elongate antennular peduncle, the more distally placed tip of the antennular stylocerite, which reaches nearly the distal margin of the peduncular article 1 (Anker 2011: fig. 1A), the more deeply incised distolateral margin of the uropodal exopod (Anker 2011: fig. 1N), and the ventromesial carina of the article 1 of the antennular peduncle forming a blunt convexity (Anker 2011: fig. 1E).
16S sequences (502 bp) were obtained from the two paratypes of the new species (KAUM-AT 902, female from Kiire, and KAUM-AT 1352, female from Kimotsuki). They are very similar for one another with only one base pair difference. The genetic divergence between R. palmeri is 11.8–12.1%, well supporting that the two taxa are specifically distinct.
The present new species is the first representative of Richalpheus to be recorded from Japan with certainty. In Japan's red list of marine creatures (Ministry of Environment, Government of Japan 2017), R. palmeri is listed and ranked as DD (data deficient), but no information on the occurrence is provided or no voucher specimens could be located.
Etymology. From the combination of the Latin words, laeua (= bulge) and digitus (= finger), in reference to the bulge-like ridge on the occlusal margin of the major cheliped dactylus in the new species. Used as a noun in apposition.
description: Published as part of Komai, Tomoyuki & Koreeda, Reo, 2022, A new species of the infaunal alpheid shrimp genus Richalpheus Anker & Jeng 2006 (Decapoda: Caridea) from Kagoshima, Japan, pp. 397-408 in Zootaxa 5115 (3) on pages 398-407, DOI: 10.11646/zootaxa.5115.3.5, http://zenodo.org/record/6358394