Eiconaxius latirostrum, Komai & Tsuchida & Fujiwara, 2024

Komai, Tomoyuki, Tsuchida, Shinji & Fujiwara, Yoshihiro, 2024, Two new species of the sponge associated axiid shrimp genus Eiconaxius Bate, 1888 (Decapoda: Axiidea) from seamounts in the Nishi-Shichito Ridge, Japan, Zootaxa 5537 (3), pp. 357-376 : 360-367

publication ID	https://doi.org/ 10.11646/zootaxa.5537.3.4
publication LSID	lsid:zoobank.org:pub:BADEE1A9-DCA2-481A-AFA6-7D18F112399B
DOI	https://doi.org/10.5281/zenodo.14248113
persistent identifier	https://treatment.plazi.org/id/03A487BE-3271-2278-FF5C-F9EE0999610D
treatment provided by	Plazi
scientific name	Eiconaxius latirostrum
status	sp. nov.

Treatment

Eiconaxius latirostrum sp. nov.

[New Japanese name: Kaizan-yadori-ana-ebi]

( Figs. 3–6 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Holotype: JAMSTEC 105682, female (cl 4.2 mm; DNA voucher), R / V Kaimei , KM20-10 C, KM-ROV dive #123, Shoho Seamount, Nishi-Shichito Ridge, Japan, 32°19.39´N, 138°44.48´E, 456 m, 28 November 2020, associated with Farrea sp. picked up by manipulator. GoogleMaps

Paratype: JAMSTEC 117424, 1 female (cl 2.9 mm), same data as holotype; JAMSTEC 105689, 1 female (cl 3.7 mm), R / V Kaimei, KM20-10 C, KM-ROV dive #123, Shoho Seamount, Nishi-Shichito Ridge, 32°19.78´N, 138°44.29´E, 401.5 m, 28 November 2020, associated with Farrea sp. picked up by manipulator GoogleMaps .

Diagnosis. Rostrum evenly tapering to rounded apex, 1.1 times as long as wide; lateral margins smooth or faintly dentate. Carapace median gastric carina sharply delimited, unarmed; submedian gastric carinae absent; lateral gastric carinae distinct, diverging posteriorly without constriction; surface glabrous. Telson posterior margin truncate, with tiny median spine. Major cheliped merus lower margin with 2 tiny denticles distally; palm not wider distally at midpoint; palm lateral and mesial faces without tubercles; palm distolateral margin without teeth in shallow gape; fixed finger occlusal margin with 1 low, small tooth proximally, without conspicuous notch; dactylus occlusal margin with blunt tooth proximally, shallow concavity and faintly crenulate distal part. Minor cheliped palm distolateral margin with 2 small acute teeth at base of dactylus; fixed finger occlusal margin weakly crenellate. Pereopods 3–5 dactyli with few spiniform setae on lateral surfaces.

Description. Body ( Fig. 3A, B View FIGURE 3 ) robust. Carapace ( Fig. 4A, B View FIGURE 4 ) smooth, compressed laterally; dorsum with sparse setae, including pair of tufts on cardiac region. Rostrum 0.2 carapace length, falling slightly short of midlength of article 2 of antennular peduncle, evenly tapering to rounded apex, 1.1 times as long as wide; dorsal surface generally concave, lateral margins raised, almost smooth or faintly dentate; middorsal carina clearly delimited, extending from 0.8 length of rostrum to anterior part of gastric region, depressed below level of lateral carinae in distal half of rostrum, posterior end not widened; ventral surface rounded, unarmed. Carapace gastric region slightly inflated, sloping to rostrum; submedian gastric carinae absent; gastric lateral carinae continuing from rostral lateral margins, diverging gradually toward posterior without distinct constriction.Antennal lobe obtuse.Anterolateral margin gently sinuous with rounded pterygostomial margin. Cervical groove absent. Cardiac notch evenly concave.

Pleon ( Fig. 4C View FIGURE 4 ) depressed dorsoventrally, with sparse setae arranged symmetrically. First pleuron ventrally rounded; second pleuron posteroventral angle not produced, only angular; third pleura posterolateral margin bluntly angular; fourth and fifth pleura rounded. First to sixth tergites all rounded. Sixth pleomere posterolateral process triangular with subacute apex; pleuron subtriangular, with minute denticle apically; posterodorsal margin smooth. Telson ( Fig. 4D View FIGURE 4 ) 1.3 times as long as wide, widest at 0.2 length, then tapering slightly to blunt posterolateral angles; lateral margins with minute, obsolescent denticles, posterior margin roundly truncate with tiny median spine; dorsal face with few short setae.

Eyestalk ( Fig. 4A, B View FIGURE 4 ) reaching mid-length of rostrum; cornea globular, pigmented with brown in preservative, ommatidia greatly reduced.

Antennular peduncle ( Fig. 4A, B View FIGURE 4 ) falling short of end of fourth article of antennal peduncle.First article unarmed. Third article 3 shorter than second article. Flagella ( Fig. 3A, B View FIGURE 3 ) subequal in length to carapace.

Antennal peduncle ( Fig. 4A, B View FIGURE 4 ) with first article unarmed. Second article with distolateral angle produced into elongate triangular blade, reaching nearly distal margin of third article of antennular peduncle. Scaphocerite a vertical blade, elongate, falling slightly short of distal end of fifth article. Third article lower margin with conspicuous distomesial spine. Fifth article about half-length of fourth article.

Third maxilliped ( Fig. 7A View FIGURE 7 ) coxa unarmed. Basis with minute spine on lower distal margin. Ischium crista dentata consisting of row of minute blunt denticles. Merus slightly narrowing distally, unarmed. Carpus widened distally, unarmed. Propodus slightly concave on lower margin, subequal in length to carpus. Dactylus distinctly about half-length of propodus. Exopod well-developed, flagellum-like, not reaching mid-length of merus, multi-articulate.

Chelipeds (first pereopods) massive ( Fig. 3A, B View FIGURE 3 ), compressed laterally, dissimilar from left to right, but subequal in length. Major cheliped ( Figs. 5A View FIGURE 5 , 6A View FIGURE 6 ; left in holotype, right in two paratypes) ischium with 2 tiny spines on lower margin. Merus upper margin bluntly carinate, noticeably convex in outline, unarmed; lower margin nearly straight, with 2 unequal spines distally; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin gently convex, not carinate, unarmed; lower margin with 1 denticle. Chela 1.9 times as long as greatest width. Palm not wider distally at midpoint, 1.2 times as long as greatest width at midpoint; upper margin sharply carinate, slightly arched, unarmed, terminating in tiny spine distally; lateral surface gently convex, almost glabrous, devoid of tubercles, with distinct keel-like carina along lower margin, extending onto fixed finger; distolateral margin slightly produced into wide convexity; mesial surface devoid of tubercles, but with scattered tufts of short setae near base of fingers, distomesial margin nearly straight; lower margin nearly straight. Fixed finger about 0.6 times as long as upper palm, nearly straight, terminating in subacute tip; mesial face with deep excavation along occlusal margin, delimited by distinct longitudinal ridge; occlusal margin with shallow, rounded gape proximally and 1 small, low tooth distal to gape, remainder part faintly crenulate; no tooth in proximal gape on both lateral and mesial side. Dactylus distally curved, terminating in blunt tip crossed with tip of fixed finger; upper margin sharply carinate; lateral surface shallowly sulcate along upper margin; mesial surface smooth; occlusal margin with 1 blunt proximal tooth and shallow concavity, remaining part only faintly denticulate.

Minor cheliped ( Figs. 5B View FIGURE 5 , 6B View FIGURE 6 ; right in holotype, left in two paratypes) ischium with 1 tiny tubercle on lower margin. Merus upper margin bluntly carinate, noticeably convex, unarmed; lower margin with 1 tiny distal spine, followed by faint denticles; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin not carinate, unarmed; lower margin with 1 tiny denticle. Chela 2.1 times as long as greatest width. Palm slightly widened distally, 1.1 times as long as greatest width; upper margin slightly arcuate, sharply carinate, unarmed, terminating in small spine distally; lateral surface gently convex, smooth, with distinct keel-like carina along lower margin, extending onto fixed finger; distolateral margin oblique, with 2, sharp triangular teeth at base of dactylus; mesial surface also smooth, with scattered tufts of setae particularly in distal half, distomesial margin oblique, with 1 small tubercle at base of dactylus; lower margin faintly sinuous. Fixed finger nearly straight with slightly curved, acute tip; mesial face with deep excavation along occlusal margin, delimited by distinct longitudinal ridge; occlusal margin denticulate. Dactylus 1.2 times as long as upper palm, slightly curved, terminating in acute tip crossed with tip of fixed finger; upper margin sharply carinate; lateral surface faintly elevated along midline; mesial surface nearly flat; occlusal margin with small blunt proximal tooth, otherwise faintly denticulate. No hiatus between fingers when closed.

Second pereopod ischium lower margin unarmed. Merus upper and lower margins unarmed, former gently arcuate. Carpus widened distally, subequal in length to palm. Palm 3.1 times as long as greatest width, with scattered tufts of short to long setae on surfaces; fixed finger slightly deflexed, with tufts of setae; dactylus about half-length of palm, also with tufts of setae.

Third pereopod ischium and merus unarmed, merus upper margin gently arcuate. Carpus shorter than propodus. Propodus with 7 transverse rows of spiniform setae on lateral surface adjacent to flexor margin, each of 2 or 3 setae; flexor distal margin with 2 spiniform setae. Dactylus short (0.3 times as long as propodus), laterally compressed, ovate, spatulate, with about 7 narrowly spaced spiniform setae on convex flexor margin, plus unguis, and 2 facial spiniform setae on proximal part.

Fourth pereopod shorter than, but similar to third pereopod. Propodus with 6 transverse rows of spiniform setae, each of 1–3 setae; brush-like setae on flexor distal margin. Dactylus ovate, spatulate, with 8 spiniform setae on convex flexor margin, plus unguis, and 3 facial spiniform seta on proximal part.

Fifth pereopod shorter than third and fourth pereopods. Ischium unarmed. Merus about half-length of carpus and propodus combined, unarmed. Carpus about half-length of propodus. Propodus without transverse rows of spiniform setae, with distal brush-like setae consisting of grooming apparatus. Dactylus ovate, spatulate, with 7 spiniform setae on convex flexor margin, plus unguis, no facial spiniform setae.

First pleopod 1 short, uniramous. Second to fifth pleopods each with appendix interna.

Uropod with protopod stout, unarmed. Endopod overreaching telson posterior margin, elongate oval in shape; lateral margin serrated with about 10 teeth in distal half, distal angle not particularly produced; dorsal surface with scattered long simple setae. Exopod reaching telson posterior margin, elongate oval in shape, lateral margin serrated with row of about 20 teeth, over distal half; dorsal surface with faint longitudinal ridge proximally.

Coloration in life. Entirely whitish translucent; in holotype, rostrum and ocular peduncle with tint of pink; cornea with minute yellowish spots, representing ommatidia ( Fig. 3A, B View FIGURE 3 ).

Distribution. Presently known only from Shoho Seamount, Nishi-Shichito Ridge, at depths of 401.5– 456 m.

Remarks. Eiconaxius latirostrum sp. nov. is morphologically and phylogenetically close to E. mortenseni Sakai, 1992 . The new species is distinguished from E. mortenseni only by subtle morphological differences, as outlined below. The rostrum tapers evenly in E. latirostrum sp. nov., rather than parallel-sided in the proximal part in E. mortenseni . The major cheliped palm is devoid of tubercles on the lateral surface in E. latirostrum sp. nov., whereas there are scattered tubercles in E. mortenseni . The occlusal margin of the major cheliped fixed finger bears only one obtuse tooth proximally in E. latirostrum sp. nov., rather than having two or three blunt proximal teeth in E. mortenseni .

Etymology. The name is from the combination of the Latin latus (= wide) and rostrum (= front) in reference to the relatively wide rostrum of the new species. Used as a noun in apposition.