Eiconaxius mortenseni Sakai, 1992

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 : 506-512

Eiconaxius mortenseni Sakai, 1992

( Figs. 8–11 )

Eiconaxius mortenseni Sakai, 1992: 160–162 , figs 3, 4. –– Kensley 1996: 475 (list). –– Komai 2011: 328. –– Komai & Tsuchida 2012: 37 (list).

Type material (not examined). Holotype: ZMUC, ovigerous female (cl including rostrum 5.5 mm), Misaki , Sagami Bay, Japan, 366 m, Th. Mortensen’s Expedition, 30 June 1914.

Paratype: ZMUC, 1 ovigerous female (cl including rostrum 6.1 mm), Sagami Bay , 732 m, Th. Mortensen’s Expedition, 2 July 1914; 1 ovigerous female (cl including rostrum 6.2 mm), no other data available .

Material examined. CBM-ZC 4655, 1 male (cl 3.6 mm), 1 ovigerous female (cl 4.5 mm), SE of Ohmurodashi Bank, Izu Islands , 34°24.42’N, 139°29.49’E, 378–403 m, TRV Shin’yo-maru, 1996 research cruise, stn 10, dredge, 23 October 1996, coll. T. Komai; CBM-ZC 5293 , 1 male (cl 4.3 mm), 2 females (cl 2.2, 4.1 mm), Okinoyama Bank, Sagami Sea , 34°57.18’N, 139°40.30’E, 190–450 m, TRV Shin’yo-maru, 1996 research cruise, stn 20, dredge, 24 October 1996, coll. T. Komai; CBM-ZC 6657 , 2 males (cl 4.4, 4.7 mm), SW of Izu-ohshima Island, Izu Islands, 34°40.2’N, 139°18.0’E, 278–300 m, RV Tansei-maru , KT97-1 cruise, stn OS-1, dredge, 27 February 1997, coll. E. Tsuchida; CBM-ZC 10049 , 3 males (cl 2.8–3.4 mm), 2 females (cl 2.9, 3.4 mm), 1 ovigerous female (cl 3.3 mm), SW of Izu-ohshima Island, Izu Islands , 34°40.21’N, 139°18.62’E, 289–307 m, 24 October 2002, TRV Shin’yo-maru , 2002 research cruise, stn 29, dredge, coll. T. Komai; CBM-ZC 12741 , 2 males (cl 4.6, 5.2 mm), 1 female (cl 5.2 mm), Sagami Bay, off Jogashima , 35°07.48’N, 139°33.21’E, 233– 113 m, 13 January 2012, RV Rinkai-maru , dredge, coll. H. Kohtsuka; CBM-ZC 17545 , 1 male (cl 5.3 mm), same data as CBM-ZC 12985 (specimens of E. farreae and E. reconditus n. sp. were collected together); CBM-ZC 17525 , 2 females (cl 5.1, 5.2 mm), 1 ovigerous female (cl 6.4 mm), same data as CBM-ZC 12753 (specimens of E. farreae and E. reconditus n. sp. were collected together); CBM-ZC 17546 , 5 males (cl 3.3–5.0 mm), 2 females (cl 4.1, 5.0 mm), same data as CBM-ZC 14488; CBM-ZC 17526 , 1 male (cl 5.5 mm), same data as CBM-ZC 14488; CBM-ZC 17527 , 1 ovigerous female (cl 5.1 mm), same data as CBM-ZC 14488.

Diagnosis. Rostrum parallel-sided proximally, with rounded apex, 1.2 times as long as wide; lateral margins smooth or only faintly crenulate; ventral surface unarmed. Carapace median gastric carina sharply delimited, unarmed; submedian gastric carinae absent; lateral gastric carinae distinct, diverging posteriorly. Telson posterior margin roundly truncate. Cornea with brown pigmentation; ommatidia distinct. Major cheliped merus lower margin with few denticles distally; palm wider distally than at mid-point, with scattered tubercles on lateral and mesial faces near base of fingers, distolateral margin without teeth in gape; fixed finger occlusal margin with 2–4 blunt teeth in proximal half and with row of obsolescent teeth in distal half, no conspicuous notch; dactylus occlusal margin with blunt tooth proximally, otherwise unarmed. Minor cheliped palm distolateral margin with prominent triangular tooth at base of dactylus; fixed finger occlusal margin faintly crenellate. Pereopods 3–5 dactyli with few spinules on lateral surfaces.

Redescription. Carapace ( Fig. 8A–C ) smooth, weakly compressed laterally. Rostrum 0.2 carapace length, parallel-sided proximally, with broadly rounded apex, 1.2 times as long as wide; dorsal surface generally concave, lateral margins distinctly carinate, nearly smooth to faintly denticulate; middorsal carina sharp, extending from near apex of rostrum to anterior part of gastric region, depressed below level of lateral carinae in distal half of rostrum, elevated above lateral margins in posterior half of rostrum, posterior end not widened; ventral surface rounded, unarmed. Submedian gastric carinae absent; lateral gastric carinae continuing from rostral lateral margins, diverging posteriorly. Antennal lobe obtuse.Anterolateral margin gently sinuous with broadly rounded pterygostomial margin. Cervical groove hardly discernible. Cardiac notch distinct.

Pleon ( Fig. 8B ) depressed dorsoventrally. Pleuron 1 ventrally rounded; pleuron 2 posteroventral angle weaky produced, sharply or subacutely pointed; pleura 3 and 4 truncate, posteroventrally square; pleuron 5 rounded; pleuron 6 triangular with acute apex, flared laterally. Tergites 1–6 all rounded. Pleomere 6 posterolateral process triangular with acute apex; posterodorsal margin with row of minute denticles. Telson 1.3 times as long as wide, widest at third length, then tapering slightly to posterolateral angles; lateral margin serrate with 5 or 6 tiny denticles, posterior margin broadly convex with small median spine; dorsal face with sparse short setae.

Eyestalk ( Fig. 8B, C ) reaching third length of rostrum; cornea globular, with brown pigmentation; ommatidia distinct.

Antennular peduncle ( Fig. 8B, C ) not reaching end of antennal peduncle article 4. Peduncular article 1 unarmed.

Antennal peduncle ( Fig. 8B, C ) with article 1 unarmed. Article 2 with distolateral angle produced into elongate triangular blade, reaching nearly distal margin of antennular peduncle article 3. Scaphocerite a vertical blade, reaching midlength of article 5. Article 3 lower margin with conspicuous distomesial spine. Article 5 about half-length of article 4.

Maxilliped 3 coxa ( Fig. 11A ) with small tubercle on lower surface distally. Basis also with minute spine on lower distal margin. Ischium crista dentata with row of obsolete teeth. 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 beyond mid-length of merus, flagellum-like, multi-articulate, longest proximal article noticeably curved.

Chelipeds (pereopods 1) massive, compressed laterally, usually dissimilar from left to right, but subequal in length. Major cheliped ( Figs. 9A , 10A ) with ischium bearing few obtuse tubercles or denticles on lower mesial margin. Merus upper margin bluntly carinate, noticeably convex in outline, with 0–3 minute denticles; lower margin sharply carinate, nearly straight, with 1 or 2 sharp denticles distally; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin rounded, unarmed; lower margin with 1 denticle (sometimes obsolescent). Chela 1.8 times as long as greatest width. Palm wider distally than at mid-point, 1.2 times as long as greatest width; upper margin sharply carinate, nearly straight, unarmed in adults or with few denticles in young specimens, terminating in small spine distally; lateral surface gently convex, with some small tubercles and short setae distally, and with distinct keel-like carina along lower margin, extending onto fixed finger, distolateral margin slightly produced into broad convexity; mesial surface with scattered low tubercles and short setae distally, distomesial margin also produced into broad convexity; lower margin faintly sinuous. Fixed finger about 0.6 times as long as upper palm, slightly curved, terminating in acute or subacute tip; mesial face with deep excavation along occlusal margin, delimited by distinct longitudinal ridge; occlusal margin with 2–4 low, blunt teeth in proximal half and row of tiny, often obsolescent teeth in distal half, without conspicuous notch or excavation. Dactylus distally curved, terminating in subacute tip crossed with tip of fixed finger; upper margin sharply carinate; lateral surface shallowly sulcate along midline at least in proximal half; mesial surface bluntly carinate along midline; occlusal margin with 1 blunt proximal tooth, otherwise faintly sinuous.

Minor cheliped ( Figs. 9B , 10B ) with ischium unarmed on lower margin. Merus upper margin bluntly carinate, noticeably convex, unarmed; lower margin with few minute denticles distally; lateral and mesial faces smooth, unarmed. Carpus distinctly wider than long; upper margin rounded, unarmed; lower margin with 1 small denticle. Chela twice as long as greatest width. Palm widened distally, almost as long as greatest width; upper margin nearly straight, sharply carinate, unarmed, terminating in small spine distally; lateral surface gently convex, without tubercles or spines, with distinct keel-like carina along lower margin, extending onto fixed finger, distolateral margin oblique, with distinct triangular tooth at base of dactylus; mesial surface also unarmed, with scattered tufts of setae, distomesial margin oblique, with tiny 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 slightly or faintly denticulate. Dactylus 1.5 times as long as upper palm, slightly curved, terminating in acute tip crossed with tip of fixed finger; upper margin sharply carinate; lateral surface bluntly elevated along midline; mesial surface nearly flat; occlusal margin with low, obtuse tooth proximally, otherwise faintly denticulate or crenulate. No hiatus between fingers when closed.

Pereopod 2 ( Fig. 11B ) with ischium unarmed on lower margin. Merus upper and lower margins unarmed. Carpus widened distally, subequal in length to palm upper margin. Palm 3.3 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. 11C ) with ischium and merus unarmed. Carpus shorter than propodus. Propodus with 6 or 7 transverse rows of spiniform setae on lateral surface adjacent to flexor margin, each of 2 or 3 setae. Dactylus ( Fig. 11D ) short (0.3 times as long as propodus), laterally compressed, ovate, spatulate, with about 10 closely spaced spiniform setae on convex flexor margin, plus unguis, and 2 or 3 facial spiniform setae on proximal part.

Pereopod 4 ( Fig. 11E ) shorter than, similar to pereopod 3. Propodus with 7 rows of spiniform setae, each of 2 or 3 setae. Dactylus ( Fig. 11F ) ovate, spatulate, with 7 or 8 spiniform setae on convex flexor margin, plus unguis, and 2 or 3 facial spiniform seta on proximal part.

Pereopod 5 ( Fig. 11G ) 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 ( Fig. 11H ). Dactylus ( Fig. 11H ) ovate, spatulate, with 7 or 8 spiniform setae on convex flexor margin, plus unguis, no facial spiniform setae.

Branchial formula as summarized in Table 2 .

Pleopod 1 absent in males; consisting of 2 articles, uniramous in females. Pleopod 2 with appendix masculina shorter than appendix interna in males ( Fig. 8G ). Pleopods 3–5 each with appendix interna.

Uropod ( Fig. 8F ) with protopod stout, unarmed. Endopod slightly overreaching telson posterior margin, elongate oval in shape, 2.1–2.3 times as long as broad; lateral margin serrated with 12–13 small teeth, distal angle not particularly produced; dorsal surface with faint longitudinal ridge and scattered long simple setae. Exopod reaching telson posterior margin, elongate oval in shape, 1.7–1.8 times as long as wide; lateral margin serrated with row of 14–20 teeth, increasing in size distally, over distal four-fifths; dorsal surface with faint longitudinal ridge.

Eggs large, c. 1.7 mm in diameter.

Coloration in life. Not available, but possibly similar to E. farreae .

Size. Largest male cl 5.5 mm; largest female cl 6.4 mm, ovigerous females cl 4.5–6.4 mm.

Distribution. Presently known only from Sagami Bay and adjacent waters, at depths of 113– 732 m.

Habitat. Found in association with Farrea sp.

Remarks. Eiconaxius mortenseni was described by Sakai (1992) based on three specimens from Sagami Bay, Japan, at depths of 366– 732 m. Since then, Komai (2011) recorded the species from the Sagami Sea off Izu-ohshima Island, Izu Islands.

Eiconaxius mortenseni is characterized by the rostrum with parallel proximal margins and rounded distal margin, the unarmed median gastric carina on the carapace, the absence of gastric submedian carinae, the possession of lateral gastric carinae, the tuberculated lateral and mesial faces of the major cheliped palm, the presence of a distinct proximal tooth on the major cheliped dactylus and the possession of a few corneous spinules on the outer face of the dactyli of pereopods 3–5. In the original description, Sakai (1992) compared E. mortenseni with E. demani , known from Indonesia, Papua New Guinea and New Caledonia ( Poore 2020). As Sakai (1992) noted, E. mortenseni is distinguished from E. demani by the lack of gastric submedian carinae and the absence of a prominent tooth on the occlusal margin of the major cheliped fixed finger. Additional differentiating characters between the two species are (cf. Poore 2020): the major cheliped palm distolateral margin is unarmed in the gape in E. mortenseni , rather than having two teeth in the gape in E. demani ; the occlusal margin of the major cheliped fixed finger is devoid of conspicuous notch in E. mortenseni , whereas there is a deep proximal notch in E. demani .

As Komai et al. (2010) discussed, E. kensleyi Komai, Lin & Chan, 2010 and E. rubrirostris Komai, Lin & Chan, 2010 , both described from Taiwan, are substantially similar to E. mortenseni . Nevertheless, E. mortenseni differs from E. kensleyi and E. rubrirostris in the broader, less acute rostrum with proximally parallel lateral margins and the possession of scattered tubercles on the lateral and mesial faces of the major cheliped palm. In E. kensleyi and E. rubrirostris , the rostrum is narrower, evenly tapering to a subacute or blunt apex; the major cheliped palm is devoid of tubercles on the lateral and mesial faces ( Komai et al. 2010).

Figures

FIGURE 8. Eiconaxius mortenseni Sakai, 1992, male (cl 5.5 mm), CBM-ZC 17526. 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 9. Eiconaxius mortenseni Sakai, 1992, male (cl 5.5 mm), CBM-ZC 17526. A, major (left) cheliped, lateral view; B, minor (right) cheliped, lateral view.

FIGURE 10. Eiconaxius mortenseni Sakai, 1992, male (cl 5.5 mm), CBM-ZC 17526. A, major (left) cheliped, mesial view; B, minor (right) cheliped, mesial view. Setae omitted.

FIGURE 11. Eiconaxius mortenseni Sakai, 1992, male (cl 5.5 mm), CBM-ZC 17526, 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.