Bouvieraxius keiensis Sakai 1992
Creators: name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Axiidae
Bouvieraxius
Bouvieraxius keiensis

description: Bouvieraxius keiensis Sakai, 1992
[New Japanese name: Bonin-Bouvier-ana-ebi]
(Figs. 1–5)
Bouvieraxius keiensis Sakai, 1992: 166, figs. 8, 9.— Sakai 2011: 80. –– Poore 2020: 277, fig. 1D, E.
Bouvieraxius rudis. — Sakai 1994: 177. Not Bouvieraxius rudis (Rathbun, 1906).
? Bouvieraxius michelae Poore, 2008: 162–164, fig. 1.
? Bouvieraxius keiensis. — Poore & Collins 2009: 244, figs. 15, 16, 41.
Material examined. CBM-ZC 16167, male (cl 7.1 mm), RV “Tansei-maru”, KT-09-2 cruise, stn TW-2-3, W of Chichi-jima Island, Ogasawara Islands, 27°03.03’N, 142°05.29’E, 165–167 m, 19 March 2009, biological dredge with 1 m width opening, coll. T. Komai.
Description of newly collected specimen. Body (Fig. 1) moderately slender; integument moderately firm.
Rostrum (Fig. 2 A–C) narrowly triangular with acute tip in dorsal view, directed forward, nearly straight, reaching slightly beyond distal margin of article 1 of antennular peduncle, about 0.5 times as long as distance between rostral base and cervical groove or 0.3 times as long as carapace; lateral margins elevated, each with 2 (right) or 3 (left) small, evenly spaced, asymmetrically arranged spines anterior to supraocular spine at rostral base, continuous with unarmed lateral gastric carina reaching midway between rostral base and cervical groove; dorsal surface shallowly concave. Carapace (Fig. 2A, B) generally smooth, with sparse, erect setae on gastric region, postcervical dorsum and lateral surface with scattered minute setae; dorsal profile in lateral view nearly straight, anterior gastric region slightly sloping down to rostrum; median gastric carina distinct, extending from anterior to level of supraocular spines to cervical groove, unarmed; submedian carinae consisting of 4 moderately spaced spines; intercarinal spaces without armature; no trace of postcervical carina; cervical groove distinct, extending to carapace anterolateral margin; suborbital lobe obtusely angular; pterygostomial margin slightly produced, rounded; cardiac notch deep.
Thoracic sternite 7 with shield (Fig. 2D) divided by deep median groove, lateral margins strongly elevated, subtriangular with sharply pointed tip.
Pleon (Fig. 2E) glabrous in anterior 4 pleomeres, pleomeres 5 and 6 with few paired erect setae. Pleomere 1 widening posteriorly in dorsal view, anterodorsal margin excavate; pleuron narrowly triangular with blunt tip, produced as far as ventral margin of pleuron 2. Pleomere 2 with pleuron slightly asymmetrical; ventral margin unarmed, rounded at either angle. Pleomeres 3–5 each with minute anteroventral spine; posterolateral angles rounded in pleuron 3, bluntly angular in pleuron 4, bearing tiny spine on pleuron 5. Pleomere 6 pleuron gently convex on ventral margin, bearing small posteroventral spine; posterolateral projection blunt.
Telson (Fig. 2F) subrectangular, 1.6 times as long as maximal width at anterolateral lobes; lateral margins nearly straight and subparallel, with conspicuous anterolateral lobe terminating posteriorly in small spine, and 2 pairs of small, widely spaced spines; posterior margin convex, with conspicuous posteromedian spine, fringed with numerous long setae and 4 or 5 minute spiniform setae, each posterolateral area with 1 strong spiniform setae; dorsal face shallowly sulcate medially, armed with 2 pairs of small spines, anterior spines located slightly anterior to midlength and posterior spines at about midlength of telson and distinctly lateral to former; long setae arising at bases of dorsal spines.
Eyestalk (Fig. 2A, B) reaching slightly beyond mid-length of rostrum, constricted at base of cornea; cornea hemispherical, subequal in length and width to eyestalk, pigmented.
Antennular peduncle (Fig. 2A, B, G) reaching midlength of antennal peduncle article 5, subcylindrical; statocyst lobe on article 1 unarmed; articles 2 and 3 combined shorter than article 1; flagella subequal in length to carapace.
Antennal peduncle (Fig. 2A, B, G) with article 1 bearing 1 small spine at ventrodistal margin; article 2 with straight dorsolateral distal spine reaching beyond mid-length of scaphocerite; scaphocerite simple, acuminate, falling short of distal end of article 4; article 3 with 1 small spine at ventromesial distal angle; article 4 subequal in length to article 2 (except for dorsolateral distal spine), slightly widened distally; article 5 about half-length of article 4; flagella subequal in length, about twice of carapace length, articles with setae of one to three article-length every 3 or 4 articles, each article with few minute setae (all setae arising distal margin).
Mouthparts not dissected. Maxilliped 3 (Fig. 3A, 5A) moderately slender. Coxa with conspicuous, anteriorly curved spine ventrally. Basis also with conspicuous spine at ventrodistal angle. Ischium with distomesial angle produced into strong, acutely pointed projection; crista dentata consisting of row of 18 sharp teeth diminishing in size proximally (Fig.); dorsolateral margin sharply keeled; ventral margin with 2 small spines in proximal half. Merus with 5 spines on ventral margin noticeably becoming larger distally; dorsolateral margin sharply keeled. Carpus with 1 small spine at flexor distal angle. Dactylus slightly shorter than propodus. Exopod not reaching distal margin of merus, its distal 0.3 flexible with multiple subdivisions.
Chelipeds (pereopods 1; Figs. 1, 4) subequal in length, right somewhat stouter than left; mero-carpal articulation with about 30° of torsion from perpendicular (left with clockwise torsion, right with counter-clockwise torsion).
Right (major) cheliped (Fig. 4 A–E; 5B) coxa bearing few spinules on distomesial margin. Basis unarmed. Ischium short, unarmed on upper margin; lower margin with distal tubercle and 1 small subdistal spine followed by 4 minute denticles. Merus generally widened distally, almost glabrous; upper margin gently arcuate in distal 0.4, sharply carinate, with 3 small subdistal spines; lateral face generally convex, distoventrally with deep excavation delimited by distinct ridge and fitting lower (flexor) margin of carpus, when cheliped flexed; distolateral angle with small articular condyle; mesial face somewhat flattened; lower margin sharply carinate, bearing 5 spines, becoming stronger toward distal, distalmost spine located at distal 0.8 of merus. Mero-carpal articulation with strong counterclockwise torsion of about 45° from perpendicular. Carpus short, as long as high, cup-shaped, unarmed. Chela large, elongate subovate with slightly convex lower margin, 2.8 times as long as high, leaving narrow hiatus between fingers; palm 1.6 times as long as high; upper margin with 1 small distal spine and row of about 30 small, blunt, truncate denticles on sharply delimited carina, no setae; lateral surface gently convex, covered with scattered numerous small tubercles (tubercles larger on lower side); mesial face less convex, more sparsely tuberculate, with very sparse, short setae; lower margin rounded in proximal half and distinctly keeled in distal half, keel extending onto fixed finger beyond midlength and bearing low, scale-like tubercles around base of fixed finger; fixed finger with irregular rows of tufts of setae on lateral and mesial faces, occlusal margin slightly concave in proximal 0.6, bearing row of small blunt teeth in distal 0.4, terminating in blunt tip. Dactylus 0.8 times as long as palm, with sparse setae becoming longer distally; upper margin carinate, with row of minute denticles in proximal half; lateral and mesial surfaces bluntly carinate along midline; occlusal margin with 2 obtuse teeth, distal half minutely denticulate.
Left (minor) cheliped (Fig. 4 F–H; 5C) with coxa to carpus generally similar to those of major cheliped. Ischium with 1 small subdistal spine followed by 6 minute denticles on lower margin. Merus with 3 subdistal spines on upper margin; lower margin with 5 spines, distalmost spine distinctly larger than others. Mero-carpal articulation with clockwise torsion of about 45° from perpendicular. Chela 3.3 times as long as high, lower margin slightly convex. Palm 1.5 times as long as high, upper margin keeled, with 1 distal spine and row of 26 small tubercles; lateral surface with covering small tubercles, those adjacent to lower margin largest. Fixed finger with sinuous occlusal margin, bearing row of minute, blunt to acute teeth over entire length; lateral and mesial faces with tufts of short to long setae. Dactylus 1.3 times as long as palm, with sparse setae; upper margin carinate, with row of denticles on proximal half; occlusal margin faintly sinuous, with row of minute teeth similar to those on fixed finger.
Pereopod 2 (Fig. 3B) slender, with setation as figured. Ischium unarmed. Merus with 4 small, widely spaced spines on lower margin. Carpus slightly widened distally. Chela 1.3 times as long as carpus; fixed finger nearly straight, slightly deflexed, occlusal margin with row of minute spiniform setae in distal half; dactylus 0.8 times as long as palm, slightly curved, terminating in slender corneous claw.
Pereopod 3 (Figs. 3C, 5D) slender, with sparse long setae. No female-type gonopore on either coxa (Fig. 2D). Ischium unarmed. Merus with 1 small spine at lower lateral distal angle, otherwise unarmed. Carpus about halflength of propodus, unarmed. Propodus with 8 evenly spaced, minute spiniform setae, increasing slightly in length toward distal, on lateral surface adjacent to lower (flexor) margin, lower distal margin with 2 minute spiniform setae. Dactylus 0.4 times as long as propodus, nearly straight, strongly compressed laterally, terminating in minute corneous unguis; lateral surface with 1 proximal spiniform seta adjacent to lower (flexor) margin; mesial surface unarmed; lower (flexor) margin with row of 11 minute, subequal spiniform setae.
Pereopod 4 (Fig. 3D, 5E) as slender as and slightly shorter than pereopod 3. Coxa with few spinules on mesial face (Fig. 2D). Ischium to carpus unarmed. Propodus lateral surface with row of 5 widely spaced minute spiniform setae adjacent to upper (extensor) margin and with 6 sets of 2 minute spiniform setae and 2 individual spiniform setae along lower (flexor) margin, distally with grooming apparatus consisting of cluster of stiff setae and 1 long spiniform seta on lower distal margin. Dactylus 0.6 times as long as propodus, nearly straight, terminating in corneous tip; lateral surface with row of 7 spiniform setae, increasing in length distally; lower (flexor) margin with row of 12 minute spiniform setae over entire length; mesial face unarmed.
Pereopod 5 (Figs. 3E, 5F, G) neither chelate nor semichelate. Coxae each with gonopore (Fig. 2D). Ischium to carpus unarmed. Propodus with grooming apparatus consisting of 1 minute spiniform seta on lower distal margin and cluster of setae extending from distal 0.3 of propodus, extending distally onto lateral surface; lateral surface unarmed; mesial surface with 1 subdistal set of 2 spiniform setae and 1 widely separated individual spiniform seta adjacent to lower (flexor) margin. Dactylus slender, nearly straight, 0.6 times as long as propodus, terminating in basally demarcate, acute unguis; upper (extensor) margin subterminally with 3 slender spiniform setae; mesial surface with 3 sets of 2 or 3 slender spiniform setae and subterminal, oblique row of 5 long spiniform setae; lower margin unarmed.
Male pleopod 1 (Fig. 5H, I) modified as gonopod, strongly flattened, articulation between 2 articles obscure; article 1 slightly widened distally; article 2 somewhat expanded mesially into roundly triangular lobe, bearing adhesive hooks proximomesially, distally divided into greatly unequal lobes; lateral lobes rounded distally, lower mesial portion vertically expanded; mesial lobe tapering into slender process far falling short of distal margin of outer lobe. Male pleopod 2 (Fig. 5J, K) with appendix masculina arising at midlength of endopod, elongate, about as long as endopod, extending beyond endopod by half its length, laterally compressed, with moderately long stiff setae on distal half of upper margin and distal 0.7 of lower margin; appendix interna also arising at midlength of endopod, rod-like, about 0.3 length of appendix masculina; endopod and exopod slender, sparsely setose, latter slightly longer than former. Pleopods 2–5 linear, without appendix interna.
Uropod (Fig. 2H) with endopod about 1.8 times as long as wide, nearly straight lateral margin with row of 3 small spines on posterior half (posterolateral spine largest); median ridge on dorsal surface with row of 3 spines, posteriormost spine far remote from posterior margin; posterior margin with row of slender spiniform setae. Exopod slightly longer than endopod; lateral margin straight, with 3 small spines, increasing in size posteriorly, on posterior half and with 1 strong spiniform seta just mesial to posterolateral spine; longitudinal row of 3 tiny spines lateral to midline; transverse suture serrate with row of 9 spinules; posterior margin.
Colour in life. Carapace dorsum orange-yellow, lateral surface whitish; cervical groove also whitish; pleon with white median stripe extending from pleomere 1 to 6, flanked by wide, orange-yellow longitudinal stripes, lateral surfaces each with white longitudinal stripe, pleura 1–6 paler orange-yellow; tail fan translucent, with tint of orange on telson and uropodal endopod; cornea grayish; antennular peduncle and flagella pale orange-yellow; antennal peduncle also pale orange-yellow, flagellum becoming reddish distally; cheliped meri translucent proximally, orange distally; carpi pale orange-yellow; chela dorsal parts orange (including dactyli of which dorsal margin white), ventral parts whitish; pereopods 2–5 and pleopods semi-translucent (Fig. 1).
Distribution. Previously known from Kai Islands, Banda Sea, Indonesia (type locality); Papua New Guinea; North-western Australia; Timor Sea; Vanuatu; Mauritius; Mozambique Channel; 73–750 m (Poore 2020). Newly recorded from Ogasawara Islands, Japan.
Remarks. Bouvieraxius keiensis was originally described based on material from two remote localities in the Indo-West Pacific, viz. Kai [sic Kei] Islands, Indonesia (type locality) and Mauritius (Sakai 1992). Sakai’s (1992) description was largely based on the holotype, supplemented by a brief description of the allotype, but his figures of the body and anterior cephalothorax was of the non-type specimen from Mauritius (Sakai 1992: fig. 8A–C), those of chelipeds were of the male holotype (Sakai 1992: fig. 8D, E) and that of the telson and left uropod was of the allotype (Sakai 1992: fig. 8F). None of these specimens was intact, and pereopods 3–5 were missing (Sakai 1992). Poore & Collins (2009) identified material from the region of Shark Bay, central Western Australia, as B. keiensis, documenting variations in the number of spines on the gastric submedian carina, spines on the cheliped merus and extent of tuberculation on the cheliped palm; they synonymised Bouvieraxius michelae Poore, 2008 under B. keiensis. They provided detailed illustrations of their material, including pereopods 2–5. Poore (2020) added further records of B. keiensis from Papua New Guinea, Vanuatu and Mozambique Channel, confirming the occurrence of the species in the western Indian Ocean; colour images of two specimens from Papua New Guinea were published, documenting the living colouration of the species for the first time.
There are some discrepancies between the present specimen and the previous accounts of B. keiensis (cf. Sakai 1992; Poore & Collins 2009; Poore 2020). The following minor differences are noted from the holotype (the condition in the holotype is noted in parentheses): the carapace lateral surface bears scattered minute setae (versus “smooth”); the pleonal pleuron 5 is sharply pointed at the posteroventral angle (versus rounded); the maxilliped 3 ischium is armed with only two spines on the lower margin (versus with three spines); the merus of each cheliped is armed with three subdistal spines on the upper margin (with four spines); tubercles adjacent to the lower margin of the cheliped palm lateral surface are distinctly larger than other tubercles (versus tubercles are similar in the size); the pleopod 1 distal article seems to be wider in the present specimen than in the holotype (cf. Fig. 5H, I versus Sakai 1992: fig. 9A); the pleopod 2 appendix masculina is less setose in the present specimen than in the holotype (cf. Fig. 5J, K versus Sakai 1992: fig. 9B–D). Furthermore, Sakai (1992) noted that the species was hermaphroditic, because every specimen has gonopores on both coxae of the pereopods 3 and 5, although the pleopods 1 and 2 were of gonochoristic form. The present specimen, attributed to a male, is much smaller than the holotype (cl 7.1 mm versus cl 20.0 mm), and those differences might be due to size-related variation. The minute setae on the carapace could be only observed with stain with methylene blue, and it is possible that those minute setae were overlooked in the original description.
Differences between the present specimen and the description by Poore & Collins (2009) include: the carapace lateral surface bears scattered minute setae (versus apparently glabrous); the pleonal pleuron 5 is sharply pointed at the posteroventral angle (versus rounded); the cheliped ischium lower margin is armed with five spines or spinules (versus armed with two to four spines); the pleopod 1 distal article is wider with more strongly expanded mesial margin in the present specimen (cf. Fig. 5H, I versus Poore & Collins 2009: fig. 15h); the transverse suture of the uropodal exopod is armed with nine spinules (versus armed with 16–20 spinules). Furthermore, the ornamentation of the cheliped palm lateral surface seems to be different. As noted above, in the present specimen, the lateral surface of the palm is covered with tubercles of different size, in particular, those adjacent to the ventral margin are distinctly larger and sharper than others (Fig. 4D, G). Poore & Collins (2009) stated: “lateral face tuberculate, especially distally near upper and lower margins”. Pereopods 2–5 of the present specimen are distinctly more slender than those illustrated by Poore & Collins (2009) (cf. Fig. 3 B–E versus Poore & Collins 2009: fig. 16a–d). Specimens studied by Poore & Collins (2009) are cl 6.0–10.0 mm, including ovigerous females of cl 8.0–10.0 mm, so those differences are not size-related.
Poore (2020) examined nine specimens (cl 5.0– 12.4 mm) from Papua New Guinea, Vanuatu and Mozambique Channel, all said to be hermaphroditic. No detailed description of those specimens was given. The present specimen is a male with gonopores only on the pereopod 5 coxae. It is remarkable that the colour and colour pattern are closely consistent between the present specimen and the two specimens from Papua New Guinea illustrated (cf. Fig. 1 and Poore 2020: fig. 1D, E), strongly suggesting the specific identity.
The relation between Bouvieraxius rudis (Rathbun, 1906) and B. keiensis is not clear. Sakai & de Saint Laurent (1989), who reexamined the female holotype from Molocai Island, Hawaii, identified specimens from Madagascar and New Caledonia as B. rudis. Sakai’s (1992; 2011) discrimination between B. keiensis and B. rudis relied chiefly on the number of spines on the submedian gastric carina, but Poore & Collins (2009) and Poore (2020) demonstrated that the number of spines ranges from three to five, even within a single individual, in specimens they referred to B. keiensis. Poore & Collins (2009) referred an ovigerous specimen from Western Australia that was identified with B. rudis by Sakai (1994) to B. keiensis. In the original description of B. rudis (as Axius), Rathbun (1906) specifically mentioned that “The carapace granulate but nearly naked.” Presence of such granules on the carapace has not been mentioned in previous accounts of B. keiensis, as well as the present specimen. For the time being, I regard the two taxa are specifically distinct, although future revisionary study is strongly recommended. The present specimen is provisionally identified as B. keiensis because of its similarity to the holotype and the consistency in the living coloration with that of specimens from Papua New Guinea illustrated by Poore (2020), geographically close to the type locality in the Banda Sea, Indonesia. Future study may eventually reveal that B. michelae is a valid species, represented by specimens from Western Australia.
Bouvieraxius is presently represented by four species (Sakai 2011; WoRMS Editorial Board 2020), including in addition to the two taxa mentioned above, B. longipes (Bouvier, 1905) from the Caribbean and B. springeri Kensley, 1996, from the Philippines. Bouvieraxius longipes resembles B. keiensis and B. rudis, but the non-tuberculate lateral surface of the cheliped palm immediately distinguishes B. longipes from the latter two species (Bouvier 1905, 1925). Bouvieraxius springeri is distinctive in the laterally unarmed rostrum and the highly crested cheliped merus, which bears a dense fringe of long setae (Kensley 1996).
description: Published as part of Komai, Tomoyuki, 2020, First record of Bouvieraxius keiensis Sakai, 1992 and Manaxius aurantiaca n. sp (Decapoda: Axiidea) from the waters around the Ogasawara Islands, Japan, pp. 369-386 in Zootaxa 4869 (3) on pages 370-378, DOI: 10.11646/zootaxa.4869.3.4, http://zenodo.org/record/4418750