Eiconaxius reconditus, Komai, 2024

Komai, Tomoyuki, 2024, Reappraisal of Eiconaxius farreae Ortmann, 1891 and Eiconaxius mortenseni Sakai, 1992 (Decapoda: Axiidea: Axiidae), with description of a new species from Japan, Zootaxa 5419 (4), pp. 495-524 : 512-519

Eiconaxius reconditus n. sp.

( Figs. 12–17 )

Eiconaxius farreae .–– Ortmann 1891: 49–50 (in part, not pl. 1 fig. 4).–– Komai et al. 2019: 11.

Type material. Holotype: CBM-ZC 17547, 1 male (cl 6.1 mm), Sagami Bay, off Jogashima , 35°06.04’N, 139°34.05’E, 364– 158 m, RV Rinkai-maru, dredge , 13 January 2012, coll. H. Kohtsuka, DNA voucher (specimens of E. farreae and E. mortenseni were collected together).

Paratypes: CBM-ZC 6769 1 male (cl 4.6 mm), Uraga Strait, off Katsuyama Ukishima Islet , 250–300 m, 16 December 2002, gill net for scampi, associated with Farrea sp. , coll. T. Komai; CBM-ZC 10054 , 1 male (cl 5.4 mm), 1 female (cl 4.8 mm), Sagami Bay, off Misaki , 35°11.51’N, 139°28.38’E, 491–580 m, RV Rinkai-maru, dredge , 16 March 2001, associated with Farrea sp. , coll. T. Komai; CBM-ZC 10099 , 1 female (cl 3.8 mm), Sagami Bay, S of Jogashima , 35°03.97’N, 139°34.8’E, 407–604 m, RV Tansei-maru , KT07-31 cruise, stn L-2’-600, 28 November 2007, dredge, associated with Farrea sp. , coll. T. Komai; CBM-ZC 14870 , 1 female (cl 6.4 mm), Sagami Bay, off Misaki , 35°06.80’N, 139°33.40’E, 407–541 m, RV Rinkai-maru, dredge , 16 February 2017, associated with Farrea sp. , coll. T. Komai, DNA voucher; CBM-ZC 17548 , 1 female (cl 5.2 mm), same data as CBM-ZC 10058 (specimens of E. farreae were collected together); CBM-ZC 17549 (ex 12753), 1 male (cl 4.9 mm), same data as CBM-ZC 12753 (specimens of E. farreae and E. mortenseni were collected together); CBM-ZC 17550 , 2 females (cl 4.8, 5.3 mm), 1 ovigerous female (cl 6.1 mm), same data as CBM-ZC 14488 (specimens of E. farreae were collected together); CBM-ZC 17551 , 3 males (cl 3.1–4.5 mm), 1 female (cl 6.1 mm), 3 ovigerous females (cl 5.4–5.7 mm), same data as CBM-ZC 16733 (specimens of E. farreae were collected together); CBM-ZC 17552 , 1 male (cl 5.9 mm), 1 female (cl 5.2 mm), same data as CBM-ZC 16730 (specimens of E. farreae were collected together).

Other material examined. Paralectotype of Eiconaxius farreae . MZS Cru4428 , 1 female (cl 5.8 mm), Sagami Bay, 100–200 fathoms (180–360 m), 1881, coll. L. Döderlein.

Diagnosis. Rostrum tapering evenly to subacute or acute apex, 1.5 times as long as wide at base; dorsolateral margins each with 1–7 minute denticles or irregularly denticulate; ventral surface unarmed. Carapace median gastric carina sharply delimited, unarmed; submedian gastric carinae absent; lateral gastric carinae distinct, diverging posteriorly. Telson with roundly truncate posterior margin. Cornea without pigmentation; ommatidia poorly developed. Major cheliped merus with few denticles on lower margin distally; palm wider distally than at mid-point, with scattered tubercles on lateral and mesial faces near base of fingers; fixed finger occlusal margin with 2–4 blunt teeth in proximal half and row of minute or faint denticles in distal half; proximal gape on palm shallow, without conspicuous tooth; dactylus occlusal margin with blunt proximal tooth, otherwise smooth, without other teeth or concavity. Minor cheliped palm distolateral margin with triangular tooth at base of dactylus, distomesial margin with small acute teeth at base of dactylus. Pereopods 3–5 dactyli with few spiniform setae on lateral surfaces.

Description. Carapace ( Fig. 12A–C ) smooth, weakly compressed laterally. Rostrum 0.2 times carapace length, concave dorsally, tapering evenly to subacute apex, 1.5 times as long as wide at base; lateral margins distinctly carinate dorsally, bearing 1–3 blunt denticles (obsolescent in large specimens), extending onto gastric region as lateral gastric carinae, diverging posteriorly; middorsal carina sharp, extending from midlength of rostrum to anterior part of gastric region, elevated above lateral margins in posterior half of rostrum, posterior end slightly widened; ventral surface rounded, unarmed. Submedian gastric carinae absent. Antennal lobe obtuse. Anterolateral margin gently sinuous with broadly rounded pterygostomial margin. Cervical groove hardly discernible. Cardiac notch distinct.

Pleon ( Fig. 12D ) compressed dorsoventrally. Pleuron 1 ventrally rounded; pleuron 2 posteroventral margin weakly produced, bluntly or subacutely pointed; pleuron 3 posteroventral margin angular or rounded; pleuron 4 posteroventral margin square; pleuron 5 rounded; pleura 3–5 each with minute anteroventral denticle; pleuron 6 triangular with acute or subacute apex, flared laterally. Tergites 1–6 all rounded. Pleomere 6 posterolateral process triangular with acute or subacute apex. Telson ( Fig. 12E ) 1.3–1.4 times as long as wide, widest at third length, then tapering slightly to posterolateral angles; lateral margins serrate with 6–8 denticles, including posterolateral one, posterior margin broadly rounded, with tiny posteromedian spine; dorsal face smooth.

Eyestalk ( Fig. 12B, C ) reaching mid-length of rostrum; cornea globular, without pigmentation even in life; ommatidia poorly developed.

Antennular peduncle ( Fig. 12B, C ) not reaching end of antennal peduncle article 4; article 1 unarmed.

Antennal peduncle ( Fig. 12B, C ) with article 1 unarmed. Article 2 with distolateral angle produced into an elongate triangular blade, reaching nearly distal margin of antennal peduncle article 4. Scaphocerite an obliquely vertical blade, reaching distal margin of article 5. Article 3 lower margin with distomesial tooth. Article 5 about half-length of article 4.

Maxilliped 3 ( Fig. 15A ) coxa with small tooth on lower distal margin. Basis lower distal margin terminating in minute spine. Ischium crista dentata bearing row of minute, obsolete denticles. Merus slightly narrowing distally, unarmed. Carpus widened distally, unarmed. Propodus slightly concave on lower margin, subequal in length to carpus. Dactylus distinctly shorter than propodus. Exopod well-developed, reaching mid-length of merus, flagellum-like, multi-articulate.

Chelipeds (pereopods 1) massive, compressed laterally, dissimilar from left to right, but subequal in length. Major cheliped ( Figs. 13A , 14A ) with ischium bearing 1 or 2 small denticles on lower mesial margin. Merus upper margin sharply carinate, noticeably convex, armed with few denticles or unarmed; lower margin with 2 denticles distally; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin rounded, unarmed; lower margin with 1 blunt denticle. Chela 1.8 times as long as greatest width. Palm slightly widened distally, 1.1 times as long as greatest width; upper margin sharply carinate, slightly convex, unarmed or armed with 1–3 denticles in addition to tiny distal spine; lateral surface gently convex, with tubercles adjacent to base of fingers, and with distinct keel-like carina along lower margin, extending onto fixed finger, distolateral margin produced into broad convexity; mesial surface also with tubercles adjacent to base of fingers, distomesial margin also produced into broad convexity; lower margin faintly sinuous. Fixed finger about 0.6 times as long as upper palm, slightly curved distally, terminating in blunt or subacute tip; mesial face with deep excavation along occlusal margin, delimited by distinct longitudinal ridge; occlusal margin with 2–4 blunt, unequal teeth in proximal half, proximal margin with small gape accommodating proximal tooth on dactylus occlusal margin, distal half minutely denticulate. Dactylus distally curved, terminating in subacute tip crossed with tip of fixed finger; upper margin carinate, sometimes with 1 denticle proximally; lateral surface shallowly sulcate along midline; mesial surface bluntly carinate along midline; occlusal margin with blunt tooth proximally.

Minor cheliped ( Figs. 13B , 14B ) ischium bearing 2–4 denticles on lower margin distally. Merus upper margin sharply carinate, noticeably convex, unarmed or armed with 1–6 denticles; lower margin at least with 1 tiny denticle distally, occasionally with few additional minute denticles; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin rounded, unarmed; lower margin with small tubercle. Chela twice as long as greatest width. Palm widened distally, approximately as long as greatest width; upper margin sharply carinate, nearly straight, unarmed or armed with 1 or 2 denticles, terminating in small spine; lateral surface gently convex, unarmed, with distinct keel-like carina along lower margin, extending onto fixed finger, distolateral margin oblique, with distinct, broadly triangular tooth, occasionally bifid distally, at base of dactylus; mesial surface also unarmed, with scattered short setae and few tufts of longer setae distally, distomesial margin oblique, with few denticles at base of dactylus; lower margin faintly sinuous. Fixed finger subequal in length to upper palm, almost straight, terminating in blunt tip; mesial face with deep excavation along occlusal margin, delimited by distinct longitudinal ridge; occlusal margin slightly denticulate entirely. Dactylus 1.2–1.3 times as long as upper palm, slightly curved, terminating in subacute tip crossed with tip of fixed finger; upper margin sharply carinate; lateral surface bluntly elevated along midline; mesial surface nearly flat; occlusal margin nearly straight, only faintly denticulate or smooth. No hiatus between fingers.

Pereopod 2 ( Fig. 15B ) with ischium unarmed on lower margin. Merus upper and lower margins unarmed, former gently arcuate. Carpus widened distally, 1.1 length of propodus upper margin. Palm 2.7 times as long as greatest width, with scattered tufts of short to long setae on surfaces; fixed finger deflexed, with numerous tufts of setae, obscuring tip; dactylus about half-length of palm, also with numerous tufts of setae, obscuring tip.

Pereopod 3 ( Fig. 15C ) with ischium and merus unarmed. Carpus 0.7 times as long as propodus. Propodus with 5 or 6 transverse rows of spiniform setae on lateral surface adjacent to flexor margin, each of 2 or 3 setae. Dactylus ( Fig. 15D ) 0.2–0.3 times as long as propodus, laterally compressed, ovate, spatulate, with 7 or 8 spiniform setae on convex flexor margin, plus unguis, and 4 facial spiniform setae on proximal part adjacent to lower margin.

Pereopod 4 ( Fig. 15E ) shorter than, similar to pereopod 3. Propodus with 5 rows of spiniform setae, each of 2 or 3 setae. Dactylus ( Fig. 15F ) ovate, spatulate, with 7 spiniform setae on convex flexor margin, plus unguis, and 4 facial spiniform seta on proximal part.

Pereopod 5 ( Fig. 15G ) 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, with distal brush-like setae consisting of grooming apparatus. Dactylus ( Fig. 15H ) ovate, spatulate, with 7 spiniform setae on convex flexor margin, plus unguis, no facial spiniform setae.

Branchial formula as summarized in Table 2 .

Pleopod 1 absent. Pleopod 2 with appendix masculina rod-like, shorter than appendix interna ( Fig. 12G ).

Uropod ( Fig. 12F ) with protopod bearing small spine on outer margin. Endopod slightly overreaching telson posterior margin, 1.7 times as long as wide, elongate-oval, outer-distal margin serrate with 7–11 teeth or denticles (distalmost one strongest), no prominent lobe distally, without longitudinal ridge on upper surface. Exopod slightly shorter than endopod, 1.4 times as long as wide, oval, not reaching endopod, outer margin serrate with 14–16 teeth in distal half, without longitudinal rib on upper surface.

Eggs large, c. 1.7 mm in diameter.

Coloration in life. Body and appendages entirely whitish; cornea reflective, without pigmentation ( Fig. 16 ).

Size. Largest male cl 6.1 mm; largest female cl 6.4 mm, ovigerous females cl 5.4–6.1 mm.

Distribution. Presently known only from Sagami Bay and nearby areas; at depth of 157– 604 m.

Habitat. Found in association with Farrea sp. ( Fig. 16 ).

Remarks. Eiconaxius reconditus n. sp. is morphologically very similar to the sympatric E. mortenseni but differs in having the rostrum evenly tapering to a subacute or acute apex and the lack of pigmentation on the cornea with poorly developed ommatidia. Genetic analyses using two mitochondrial markers support that the new taxon is distinct from E. mortenseni (see below).

Eiconaxius reconditus n. sp. is immediately distinguished from the sympatric E. farreae by the presence of lateral gastric carinae on the carapace, the absence of a deep triangular gape at the base of the fixed finger of the major chela, the presence of two or three principal teeth on the proximal half of the fixed finger occlusal margin and the presence of a conspicuous proximal tooth on the occlusal margin of the major chela.

As mentioned above, E. kumejimaensis is morphologically similar to E. reconditus n. sp. (cf. Sakai 2014). The new species differs from E. kumejimaensis in the lack of gastric submedian carinae on the carapace, the tuberculate lateral and mesial faces of the major cheliped palm, the possession of 2–4 blunt teeth on the proximal half of the occlusal margin of the major cheliped fixed finger, and the possession of a small proximal tooth on the occlusal margin of the major cheliped dactylus. In E. kumejimaensis , the gastric median carina is bifurcated posteriorly into submedian gastric ridge ( Sakai 2014: fig. 5C); the lateral face of the major cheliped palm is smooth, devoid of tubercles ( Sakai 2014: fig. 6C): the occlusal margin of the major chela fixed finger has only one obtuse tooth preceded by a row of tiny teeth ( Sakai 2014: fig. 6C); the occlusal margin of the major chela dactylus has a broad proximal tooth accompanied distally by a shallow but distinct notch ( Sakai 2014: fig. 6C). Bathymetrical range may differ between the two species: E. reconditus n. sp. occurs at depths of 157–604 m, whereas the type specimens of E. kumejimaensis came from considerable depth of 1846–1870 m ( Sakai 2014).

Reexamination of the type material of E. farreae has disclosed that one specimen (originally MZS Cru4428; Fig. 17 ) actually represents E. reconditus n. sp.. This specimen exhibits the following features diagnostic of E. reconditus n. sp.: the rostrum evenly tapers to a subacute apex, with distinct denticles on the lateral margins; the carapace is provided with lateral gastric carinae ( Fig. 17A ); the major cheliped fixed finger bears 2 low teeth on the proximal half of the occlusal margin ( Fig. 17B ); the fixed finger occlusal margin is armed with a distinct proximal tooth ( Fig. 17B ).

As shown above, the specimen from Merase Bank in Sagami Bay, referred to as E. farreae by Sakai & Ohta (2005), is not E. farreae . This specimen still differs from E. reconditus n. sp. in the possession of submedian gastric carinae on the carapace, the narrower telson, and the blade-like prominent tooth on the occlusal margin of the major cheliped fixed finger, clearly suggesting that the Sakai & Ohta’s (2005) specimen is distinct from E. reconditus n. sp.

As mentioned above, the material identified with E. farreae by Komai (2011) contained specimens of the present new species.

It has been clarified that the voucher specimen for the short fragment of the 16S rRNA gene (CBM-ZC 14870; LC464548) for eDNA metabarcoding, identified with E. farreae by Komai et al. (2019), actually represents E. reconditus n. sp.

Etymology. From the Latin word “ reconditus ” (= hidden), in reference to the situation that the new species has been confounded with E. farreae .

Figures

FIGURE 12. Eiconaxius reconditus n. sp., holotype, male (cl 6.1 mm), CBM-ZC 17547.A, carapace and cephalic appendages, lateral view (antennular and antennal flagellum omitted); B, anterior part of carapace and cephalic appendages, dorsal view; C, anterior part of carapace and cephalic appendages, lateral view; D, pleon, telson and left uropod, lateral view; E, telson, dorsal view (marginal setae omitted); F, right uropod, dorsal view (perpendicular against horizontal plane); G, appendices interna and masculina of left pleopod 2, mesial view.

FIGURE 13. Eiconaxius reconditus n. sp., holotype, male (cl 6.1 mm), CBM-ZC 17547. A, major (left) cheliped, lateral view; B, minor (right) cheliped, lateral view.

FIGURE 14. Eiconaxius reconditus n. sp., holotype, male (cl 6.1 mm), CBM-ZC 17547.A, major (right) cheliped, mesial view; B, minor (right) cheliped, mesial view. Setae omitted.

FIGURE 15. Eiconaxius reconditus n. sp., holotype, male (cl 6.1 mm), CBM-ZC 17547, left thoracic appendages, lateral view. A, left maxilliped 3; B, pereopod 2; C, pereopod 3, D, same, distal part of propodus and dactylus, lateral view; E, pereopod 4; F, distal part of propodus and dactylus, lateral view; G, pereopod 5; H, same, distal part of propodus and dactylus, lateral view.

FIGURE 16. Eiconaxius reconditus n. sp., paratype, male (cl 4.6 mm), CBM-ZC 6769, living animal, with host sponge Farrea sp. Photo taken by T. Komai.

FIGURE 17. Eiconaxius reconditus n. sp., paralectotype of E. farreae, MZS Cru4428, female (cl 5.8 mm). A, anterior part of carapace and cephalic appendages, lateral view; B, major (left) chela, lateral view.