Eiconaxius kaimei, 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 : 367-372

Eiconaxius kaimei sp. nov.

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

( Figs. 9–13 )

Material examined. Holotype: JAMSTEC 107184, ovigerous female (cl 6.2 mm; DNA voucher), R / V Kaimei , KM21 -E04C, KM-ROV dive #156, An’ei Seamount, Nishi-Shichito Ridge, Japan, 29°17.96´E, 138°37.74´E, 888 m, 17 October 2021, associated with Farrea sp. picked up by manipulator.

Diagnosis. Rostrum evenly tapering to rounded apex, 1.4 times as long as wide; lateral margins smooth. Carapace median gastric carina sharply delimited, unarmed; submedian gastric carinae absent; lateral gastric carinae distinct, diverging posteriorly without constriction; dorsum with scattered thin setae and a pair of tufts of setae on cardiac region. Telson posterior margin truncate, with tiny median spine. Major cheliped merus lower margin unarmed; palm not wider distally at midpoint; palm lateral and mesial faces with scattered tubercles; palm distolateral margin without teeth in shallow gape; fixed finger occlusal margin with 2 rounded teeth in proximal half and row of much smaller, blunt teeth in distal half, without conspicuous notch; dactylus occlusal margin with blunt tooth proximally, shallow concavity and smooth distal part. Minor cheliped palm distolateral margin with small acute tooth at base of dactylus; fixed finger occlusal margin finely denticulate. Pereopods 3–5 dactyli with few spiniform setae on lateral surfaces.

Description. Body ( Fig. 9 ) robust. Carapace ( Fig. 10A, B ) smooth, compressed laterally; dorsum with scattered thin setae and a pair of tufts of setae on cardiac region. Rostrum approximately 0.2 carapace length, reaching midlength of article 2 of antennular peduncle, evenly tapering to rounded apex, 1.4 times as long as wide; lateral margins faintly convex in dorsal view; dorsal surface generally concave, lateral margins raised, almost smooth; middorsal carina low but clearly delimited, extending nearby from tip 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 gastric carinae continuing from rostral lateral margins, diverging abruptly proximal to rostral base, but without distinct constriction.Antennal lobe obtuse.Anterolateral margin gently sinuous with rounded pterygostomial margin. Cervical groove absent. Cardiac notch evenly concave.

Pleon ( Fig. 10C ) depressed dorsoventrally, with sparse setae arranged symmetrically. First pleuron small, ventrally rounded; second pleuron posteroventral produced into subacute tooth; third pleuron posterolateral margin produced into subacute tooth; fourth pleuron posteroventral margin bluntly angular; fifth pleuron rounded. First to sixth tergites all rounded. Sixth pleomere posterolateral process triangular with acute apex; pleuron subtriangular, with minute denticle apically; posterodorsal margin smooth, without denticles. Telson ( Fig. 10D ) 1.6 times as long as wide, widest at 0.2 length, then narrowing slightly to truncate posterior margin; lateral margins with minute denticles, posterior margin with median spinule; dorsal face with longitudinal rows of tufts of short to moderately long setae.

Eyestalk ( Fig. 10A, B ) reaching mid-length of rostrum; cornea globular, no trace of ommatidia or pigmentation seen in preservative.

Antennular peduncle ( Fig. 10A, B ) falling short of end of fourth article of antennal peduncle. First article unarmed, lateral margin gently sinuous. Third article shorter than second article. Flagella ( Fig. 9 ) subequal in length to carapace.

Antennal peduncle ( Fig. 10A, B ) with first article unarmed. Second article with distolateral angle produced into elongate triangular blade, reaching distal margin of fourth article. Scaphocerite a vertical blade, elongate, reaching distal end of fifth article. Thirrd article 3 lower margin with conspicuous distomesial spine. Fifth article about half-length of fourth article.

Third maxilliped ( Fig. 13A ) coxa with minute spine on lower distal angle. Basis unarmed. Ischium crista dentata consisting of row of minute granules. Merus slightly narrowing distally, unarmed. Carpus shorter than merus, widened distally, unarmed. Propodus slightly concave on lower margin, filled with cluster of stiff setae, subequal in length to carpus. Dactylus about half-length of propodus, with cluster of stiff setae on flexor surface. Exopod well-developed, flagellum-like, overreaching mid-length of merus, multi-articulate.

Chelipeds (first pereopods) massive ( Fig. 9 ), compressed laterally, dissimilar from left to right, but subequal in length. Major cheliped ( Figs. 11A , 12A ) ischium with 3 tiny blunt tubercles on lower margin. Merus upper margin bluntly carinate, noticeably convex in outline, unarmed; lower margin faintly sinuous, unarmed; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin gently convex, bluntly carinate, unarmed; lower margin with 1 denticle. Chela 1.8 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 convex, unarmed, terminating in tiny denticle distally; lateral surface gently convex, with scattered small tubercles and tufts of short setae proximal to base of dactylus, and with distinct keel-like carina along lower margin, extending onto fixed finger; distolateral margin nearly straight; mesial surface also with scattered tubercles and tufts of setae proximal to base of dactylus, distomesial margin slightly convex; lower margin faintly sinuous. Fixed finger about half-length of 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 2 rounded teeth distal to gape, remainder part (about distal half) with row of 7 small, blunt teeth; 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 midline; mesial surface smooth; occlusal margin with 1 blunt proximal tooth and shallow concavity, remaining part entire.

Minor cheliped ( Figs. 11B , 12B ) ischium with 5 small, blunt tubercles on lower margin. Merus upper margin bluntly carinate, noticeably convex, unarmed; lower margin with 1 tiny distal spine, otherwise entire; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin bluntly carinate, unarmed; lower margin with 1 tiny denticle. Chela twice as long as greatest width. Palm slightly widened distally, approximately as long as greatest width; upper margin slightly convex, sharply carinate, unarmed, terminating in minute spine distally; lateral surface gently convex, smooth, with distinct keel-like carina along lower margin, extending onto fixed finger; distolateral margin oblique, with sharp triangular tooth at base of dactylus; mesial surface also smooth, with scattered tufts of long setae particularly in distal half, distomesial margin oblique, unarmed; lower margin slightly 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 finely denticulate. Dactylus 1.3 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 with distinct longitudinal ridge defining excavation along occlusal margin; occlusal margin with small blunt proximal tooth, otherwise almost entire. No hiatus between fingers when closed.

Second pereopod ( Fig. 13B ) ischium lower margin unarmed. Merus upper and lower margins unarmed, former gently arcuate. Carpus widened distally, subequal in length to palm. Chela 1.3 times as long as carpus; palm 2.9 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 ( Fig. 13C, D ) 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 1–3 setae; flexor distal margin without spiniform setae. Dactylus short (0.3 times as long as propodus), laterally compressed, ovate, spatulate, with about 10 narrowly spaced spiniform setae on convex flexor margin, plus unguis, and 4 facial spiniform setae on proximal part.

Fourth pereopod ( Fig. 13E, F ) shorter than, but otherwise similar to pereopod 3. Propodus with 3 transverse rows of spiniform setae (each of 2 or 3 setae) + 1 small spiniform seta; brush-like setae on flexor distal margin. Dactylus ovate, spatulate, with about 10 spiniform setae on convex flexor margin, plus unguis, and 4 facial spiniform seta on proximal part.

Fifth pereopod ( Fig. 13G, H ) shorter than pereopods 3 and 4. 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, but 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 short, uniramous. Second to fifth pleopods each with appendix interna.

Uropod ( Fig. 10E ) with protopod stout, unarmed. Endopod slightly overreaching telson posterior margin, elongate oval in shape, twice as long as wide; lateral margin serrated with about 14 teeth, distal angle not particularly produced; dorsal surface with scattered long simple setae. Exopod reaching telson posterior margin, elongate oval in shape, 1.7 times as long as wide; lateral margin serrated with row of about 23 teeth, over distal 0.6; dorsal surface with faint longitudinal ridge.

Eggs globular, large in size, measuring 1.5 mm in diameter, about 10 in number.

Coloration in life. Cephalothorax translucent with pale orange tint entirely, rostrum reddish; pleon and appendages whitish translucent; cornea opaque; eggs whitish ( Fig. 9 ).

Distribution. Presently known only from An’ei Seamount, Nishi-Shichito Ridge, at a depth of 888 m.

Remarks. Eiconaxius kaimei sp. nov. is morphologically and phylogenetically close to E. reconditus . Morphological differences between the two species are subtle: the telson is proportionally longer in E. kaimei sp. nov. than in E. reconditus (1.6 times as long as wide versus 1.3–1.4 times as long) ( Fig. 10D versus Komai 2024: fig. 12E); the merus of the major cheliped is more slender in E. kaimei sp. nov. than in E. reconditus ( Fig. 11A , 12A versus Komai 2024: figs. 13A, 14A). As mentioned above, the genetic divergences of the two mitochondrial markers are sufficient to warrant the recognition of the new taxon.

Etymology. Eiconaxius kaimei sp. nov. is named for the R/V Kaimei of JAMSTEC to honor ship’s crew and scientists on board who served to investigate the poorly surveyed areas off Japan. Used as a noun in apposition.

Figures

FIGURE 9. Eiconaxius kaimei sp. nov., holotype, ovigerous female (cl 6.2 mm), JAMSTEC 107184, habitus in lateral view.

FIGURE 10. Eiconaxius kaimei sp. nov., holotype, ovigerous female (cl 6.2 mm), JAMSTEC 107184:A, carapace and cephalic appendages, lateral view; B, anterior part of carapace and cephalic appendages, dorsal view; C, pleon, telson and uropod, left lateral view; D, telson, dorsal view (marginal setae omitted); E, left uropod, dorsal view (setae omitted).

FIGURE 11. Eiconaxius kaimei sp. nov., holotype, ovigerous female (cl 6.2 mm), JAMSTEC 107184: A, left major cheliped, lateral view; B, right minor cheliped, lateral view.

FIGURE 12. Eiconaxius kaimei sp. nov., holotype, ovigerous female (cl 6.2 mm), JAMSTEC 107184: A, left major cheliped, mesial view; B, right minor cheliped, mesial view.

FIGURE 13. Eiconaxius kaimei sp. nov., holotype, ovigerous female (cl 6.2 mm), JAMSTEC 107184, left thoracic appendages, in lateral view:A, third maxilliped; B, second pereopod; C, third pereopod; D, same, distal part of propodus and dactylus, lateral view; E, fourth pereopod; F, same, distal part of propodus and dactylus; G, fifth pereopod; H, same, distal part of propodus and dactylus.