Athanas acudactylus Komai & Henmi, 2025, sp. nov.
Creators: name: Komai, Tomoyuki
name: Henmi, Yumi
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Athanas
Athanas acudactylus

description: Athanas acudactylus sp. nov.
[New Japanese name: Aka-murasaki-ebi]
(Figs. 2–5)
Material examined. Holotype. CBM-ZC 17868, ovigerous female (cl 4.6 mm), Japan, Honshu, Wakasa Bay, off Ine, 35°45’05”N 135°19’44”E, 96 m, mud, SM grab, coll. Y. Henmi, 17 June 2022, DNA voucher (LC832870).
Paratype. CBM-ZC 15617, ovigerous female (cl 4.1 mm), Japan, Honshu, Sagami Bay, W of Jogashima, TRV Shin’yo-maru, 2015 research cruise, station 1 (T3), 35°08’13”N, 139°34’26”E, 92 m, sand, dredge, coll. H. Kohtsuka, 31 October 2015, DNA voucher (LC832871).
Description. Holotype. Body moderately robust. Carapace (Figs. 2, 3A, B) glabrous, not setose. Rostrum about half as long as carapace, slightly flattened dorsoventrally, directed forward, reaching distal end of second article of antennular peduncle, narrowly triangular with acute apex in dorsal view; rostral dorsal carina discernible. Frontal margin devoid of supracorneal spines; extracorneal spines acuminate, not reaching distal corneal margins; infracorneal spines small, not reaching extracorneal spines. Anterolateral margin nearly straight. Pterygostomial margin broadly rounded, not protruding anteriorly. Cardiac notch deep.
Pleura of first to fourth pleomeres (Fig. 2) rounded, unarmed, while that fifth pleomere (Fig. 2) acutely pointed at posteroventral angle. Sixth pleomere (Figs. 2, 3E) with articulated triangular flap posteroventrally; posterolateral process pointed but not acuminate. Telson (Fig. 3C, D) widest at proximal 0.4 of length, narrowing posteriorly, with 2 pairs of dorsolateral spiniform setae, anterior pair near telson mid-length, posterior pair at 0.7 telson length; posterior margin medially slightly convex, with1 pair of tiny posterolateral spiniform setae and long mesial plumose setae, numbering about 16.
Eyes (Fig. 3A, B) largely exposed in dorsal and lateral views; cornea well pigmented.
Antennular peduncle (Fig. 3A, B) reaching distal margin of antennal scaphocerite. Basal article subequal in length to distal 2 articles combined, second article longer than third article; stylocerite acute, reaching midlength of second article; ventromesial carina with well-developed, acute spine. Lateral flagellum biramous, fused proximal portion composed of 7 segments, aesthetasc-bearing shorter ramus composed of 5 segments.
Antennal peduncle (Fig. 3A, B) with basicerite bearing small ventrolateral distal spine. Scaphocerite oval; lateral margin straight; distal lamella produced, rounded, slightly overreaching distolateral spine. Carpocerite stout, falling slightly short of distal margin of scaphocerite.
Mouthparts without specific features, typical for genus.
Third maxilliped (Fig. 4A) with endopod slender, reaching distal margin of scaphocerite by tip of ultimate article. Ultimate article 1.6 times as long as penultimate article, tapering to subacute tip, latter bearing single subterminal seta, without spiniform setae. Antepenultimate article slightly sinuous, widened proximally. Coxal plate distal margin strongly produced into triangular process. Exopod not reaching distal end of antepenultimate article of endopod.
First pereopods (chelipeds) (Fig. 4B–E) subequal in length and similar in shape, elongate, slender, exceeding antennal carpocerite by about half-length of merus; surface of all articles smooth, devoid of teeth, spines or other conspicuous armature or ornamentation. Chela 5.2 times as long as wide; palm 3.2 times longer than wide, subcylindrical; dactylus slender, 0.7 of palm length, occlusal margin entire; pollex gently deflexed, occlusal margin also entire; fingers not gaping. Carpus elongate, gradually widening distally, 1.6 times chela length, 10.8 times longer than distal width. Merus subequal in length to carpus, faintly recurved, 11.7 times longer than central width. Ischium 0.8 times meral length, 9.6 times longer than distal width. Basis small, with rudimentary, bud-like exopod. Coxa robust.
Second pereopod (Fig. 4F) moderately slender, overreaching distal margin of scaphocerite by half-length of carpus. Ischium slightly shorter than merus. Carpus composed of 5 segments, first segment longer than four others combined; ratio of carpal segments (from proximal to distal) approximately: 3.4: 0.4: 0.4: 0.5: 1.0. Chela simple, longer than distal carpal segment, fingers slightly longer than palm.
Third to fifth pereopods slender, generally similar. Third pereopod (Fig. 4G, H) overreaching distal margin of scaphocerite by full length of propodus; ischium unarmed at distodorsal end, with 2 spiniform setae on ventrolateral surface; merus, carpus and propodus unarmed, merus 7.0 times as long as wide; dactylus simple, slender, scythe-shaped, half-length of propodus, 10.2 times as long as basal width, gently curved, with minute setae slightly distal to mid-length.Fourth pereopod (Fig.4I,J)overreaching distal margin of scaphocerite by half-length of propodus;ischium 2 ventrolateral spiniform setae; dactylus 0.6 times as long as propodus. Fifth pereopod (Fig. 4K, L) overreaching distal margin of scaphocerite by length of dactylus; ischium unarmed; propodus with grooming apparatus consisting of 5 transverse rows of microserrulate setae in distal 0.3; dactylus 0.5 times as long as propodus.
Gill formula typical for genus: pleurobranchs on to eighth thoracomeres (above bases of first to fifth pereopods); podobranch and arthrobranch absent; lobe-like epipods on first and second maxillipeds, strap-like epipods on coxae of third maxilliped and first to third pereopods; setobranchs, each consisting of single seta, present on coxae of first to fourth pereopods; first and second maxillipeds each with well-developed, flagellum-like exopod.
Second to fifth pleopods each with appendix interna on endopod.
Uropod (Fig. 3E, F) with protopod ending in 2 lobes, mesial lobe acuminate, lateral lobe terminating in 2 minute teeth. Exopod with lateral margin nearly straight, terminating in small sharp tooth; distolateral spiniform seta distinctly longer than distolateral tooth; diaeresis straight, unarmed. Endopod subovate, subequal in length to exopod.
Paratype. Generally similar to holotype. Rostrum reaching mid-length of second article of antennular peduncle. Right first pereopod relatively shorter compared to that of holotype. Chela 5.2 times as long as wide; palm 3.3 times longer than wide, subcylindrical; dactylus 0.7 of palm length. Carpus 1.3 times chela length, 9.1 times longer than distal width. Merus subequal to carpus length, faintly recurved, 10.7 times longer than central width. Ischium 0.8 times meral length, parallel-sided, 8.6 times longer than distal width. Third pereopod with dactylus 0.55 times as long as propodus.
Colouration in life. Body generally red; carapace and pleon with whitish median stripe; telson and uropods whitish posteriorly; cornea grey; antennular peduncle and antenna translucent with tinge of red, flagella translucent; third maxilliped and pereopods generally translucent, merus and ischium of first pereopod (cheliped) with tinge of red; eggs dark red (Fig. 5).
Distribution. Presently known from Japan: Wakasa Bay (Sea of Japan) and Sagami Bay (Pacific coast), at depths of 92– 96 m.
Etymology. From the Latin acus (= needle) and dactylus (= finger), referring to the slender dactyli of the third to fifth pereopods of the new species.
Remarks. Among the 43 named species of Athanas (De Grave & Fransen 2011; Ďuriš & Anker 2014; Ahyong 2015; Marin 2017; Anker & Ďuriš, 2022; Anker 2023; Komai & Henmi 2023), A. acudactylus sp. nov. appears closest to A. hongkongensis Bruce, 1990, in the combination of the following features: (1) frontal margin of carapace with extracorneal and infracorneal teeth but without supracorneal teeth; (2) chelipeds elongate, including in females, more or less symmetrical in shape and subequal in size, with slender ischium and non-inflated merus and markedly elongate carpus, without conspicuous armature on every article; and (3) third to fifth pereopods with simple, slender, scythe-shaped dactyli, attaining half or more than half-length of propodi. Athanas hongkongensis is known only by the type specimens from Hong Kong, South China Sea (Bruce 1990; Sha et al. 2019). A comparison with the original description of A. hongkongensis by Bruce (1990) revealed the following differences of possible diagnostic significance: (1) the posterolateral angle of the telson bears only one pair of spiniform setae in A. acudactylus sp. nov., whereas there are two pairs of spiniform setae in A. hongkongensis, of which the mesial pair is much longer (cf. Fig. 3C, D; Bruce 1990: fig. 7I); (2) the antennular peduncle reaches the distal margin of the scaphocerite in A. acudactylus sp. nov., rather than falling distinctly short of it in A. hongkongensis (Fig. 3B; Bruce 1990: fig. 7A, B); (3) the dactylus of the third to fifth pereopods is proportionally slightly shorter in A. acudactylus sp. nov. than in A. hongkongensis (0.5–0.6 times as long as propodus versus about 0.7 times as long); (4) the flexor margins of the propodi of the third and fourth pereopods are devoid of minute spiniform setae in A. acudactylus sp. nov., whereas some minute spiniform setae are present in A. hongkongensis (cf. Fig. 4G, I; Bruce 1990: fig. 8G, I); (5) the ischia of the third and fourth pereopods bear two spiniform setae in A. acudactylus, instead of one spiniform seta in A. hongkongensis (cf. Fig. 4G, I; Bruce 1990: fig. 8G, I); and (6) the lateral distal lobe of the uropodal protopod is ending in two acute teeth in A. acudactylus sp. nov., while being simple in A. hongkongensis (cf. Fig. 3E; Bruce 1990: fig. 7F). No genetic data are presently available for A. hongkongensis.
Bruce (1990) compared A. hongkongensis with A. polymorphus Kemp, 1915, A. gracilipes Banner & Banner, 1978 and A. tenuipes De Man, 1910. Among them, A. polymorphus is immediately distinguished from the aforementioned congeners by the presence of a pterygostomial tooth on the carapace (Kemp 1915: fig. 32a; Anker 2003: fig. 9a). The female chelipeds and the colour pattern of A. polymorphus also differs markedly from that of the new species (cf. Fig. 5 versus Anker 2003: figs. 12, 20e, f).
Athanas gracilipes was described on the basis of two fragmentary specimens, both without chelipeds (Banner & Banner 1978; Anker & Ahyong 2007). Athanas acudactylus sp. nov. differs from A. gracilipes in the longer rostrum (in the latter species, the rostrum fails to reach the distal margin of the basal article of the antennular peduncle; the distolateral tooth of the antennal scaphocerite distinctly exceeded by the anteriorly produced lamella; and in the absence of a mesial pair of spiniform setae on the posterolateral angles of the telson (cf. Banner & Banner 1978: fig. 3a–c).
Athanas tenuipes is known with certainty only from the possibly juvenile holotype, which, like A. gracilipes, lacks both chelipeds, although Anker & Ahyong (2007) mentioned a specimen from southern Vietnam possibly representing A. tenuipes. This species can be diagnosed by the narrow telson with relatively large dorsolateral spiniform setae and a truncate posterior margin, the latter also with a shallow median notch and narrowly spaced posterior spiniform setae (De Man 1911: pl. III, fig. 8b). In the new species, the telson has small spiniform setae and a broadly rounded posterior margin, with only two spiniform setae, one at each angle (Fig. 3C).
The sympatrically occurring A. exilis (see below) is readily distinguished from A. acudactylus sp. nov. by the shorter rostrum, which does not reach the distal margin of the basal article of the antennular peduncle versus overreaching it in the new species (cf. Fig. 3A, B; Komai & Henmi 2023: fig. 2B, C); the more robust female chelipeds, with row of small tubercles on the ventral margin of the merus and carpus, versus female chelipeds being slenderer and without conspicuous armature in the new species (cf. Fig. 4B, C; Komai & Henmi 2023: fig. 3D, E); the presence of long spiniform setae on the dorsal margin of the cheliped ischium, which are absent in the new species (cf. Fig. 4B, C; Komai & Henmi 2023: fig. 3D, E); and the more strongly produced distal lamella of the antennal scaphocerite (cf. Figs. 2G, 6B; Komai & Henmi 2023: fig. 3B).
description: Published as part of Komai, Tomoyuki & Henmi, Yumi, 2025, A new species of the alpheid shrimp genus Athanas Leach, 1814 (Decapoda: Caridea) from Japan, and additional record of Athanas exilis Komai & Henmi, 2023, clarifying male characteristics, pp. 353-370 in Zootaxa 5583 (2) on pages 356-361, DOI: 10.11646/zootaxa.5583.2.7, http://zenodo.org/record/14797259