Gebiacantha acanthochela ( Sakai, 1967 )

Komai, Tomoyuki, 2020, Redescription of a poorly known upogebiid mud shrimp Gebiacantha acanthochela (Sakai, 1967) and description of a new species of the genus from the Ryukyu Islands, Japan (Decapoda: Gebiidea), Zootaxa 4881 (2), pp. 307-322 : 308-314

publication ID	https://doi.org/ 10.11646/zootaxa.4881.2.5
publication LSID	lsid:zoobank.org:pub:7E570EDA-1A01-45AB-8ED2-79F8B8A6B9FE
DOI	https://doi.org/10.5281/zenodo.4328023
persistent identifier	https://treatment.plazi.org/id/03898797-FFE6-FF96-FF14-FCD5FE5EFB10
treatment provided by	Plazi
scientific name	Gebiacantha acanthochela ( Sakai, 1967 )
status

Treatment

Gebiacantha acanthochela ( Sakai, 1967) View in CoL

[New Japanese name: Tsuno-toge-ana-jyako]

( Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Upogebia acanthochela Sakai, 1967:44 View in CoL , pl. 4, fig. 2A–G; 2006: 83.—de Saint Laurent & Ngoc-Ho 1979: 63–65.— Itani, 2004: table 2 (list).— Sakai & Türkay 2014: 149 (key).

Upogebia (Upogebia) ceratophora View in CoL .— Sakai 1982: 49 (in part).

Upogebia (Upogebia) acanthochela View in CoL .— Sakai 1987: 306 (list).

Gebiacantha acanthochela View in CoL .— Ngoc-Ho 1989 a: 120 (key), 121 (list); 1994a: 198, table 1; 1994b: 60 (key); 2001: 54 (list).

Material examined. CBM-ZC 16175, 1 female (cl 9.1 mm), 1 ovigerous female (cl 8.2 mm), TRV “Toyoshio-maru”, 2009-03 cruise, stn 7, west entrance of Ohshima Strait , Amami Islands, Ryukyu Islands, 28°12.63'N, 129°10.31'E, 98–100 m, 21 May 2009, SM grab, coll. T. Komai GoogleMaps .

Type material. Holotype: ZLKU ( Zoological Laboratory , Faculty of Agriculture , Kyushu University) 12848, female (cl 7.3 mm), “Yellow Sea” (see “ Remarks ”), 100 m deep, trawl, 5 July 1962, coll. Hideo Yamashita. Not examined.

Paratypes: ZLKU 12847 , 1 male (cl 8.5 mm) collected with holotype ; ZLKU 9621 , 1 female (cl 7.8 mm), East China Sea (see “Remarks”), 29°02'N, 125°25'E, trawl, 29 June 1962, coll. H. Yamashita. Not examined GoogleMaps .

These type specimens are now preserved in the Kitakyushu Museum of Natural History, Kitakyushu, Japan.

Description of newly collected specimens. Rostrum ( Figs 1A View FIGURE 1 , 2A, B View FIGURE 2 ) subtriangular in dorsal view, reaching midlength of article 4 of antennal peduncle, 1.4 times as long as basal width, directed forward in lateral view, somewhat flattened dorsoventrally; dorsolateral margins each with 7–10 narrowly to moderately spaced, moderately small, subacutely or bluntly pointed tubercles (each tubercle directed anterodorsally), anteriormost pair subterminal in position; dorsal surface nearly flat, setose (setal field extending onto gastric region along lateral gastric ridges), with faint median sulcus proximally; ventral surface nearly straight, armed with 2 or 3 relatively small, unequal spines clustered in distal 0.2, those spines directed anteriorly or anteroventrally; rostral apex roundly truncate in lateral view, overreached by distalmost ventral spine. Carapace ( Figs. 1A View FIGURE 1 , 2A, B View FIGURE 2 ), somewhat compressed laterally; anterior part with lateral gastric ridges slightly diverging posteriorly, each terminating in small spine anteriorly and bearing row of 8 or 9 tubercles decreasing in size toward posterior; gastric region flanked by shallow grooves running along gastric lateral ridges and having 2 irregular, longitudinal rows of small tubercles, extending anteriorly to rostral base on either side; median naked area triangular, flat, unarmed; anterolateral margin with 4–6 spinules, including postocular spine; postorbital region with 1 or 2 minute granules; pterygostomial margin rounded, unarmed; linea thalassinica extending from anterolateral notch to posterodorsal end of carapace, interrupted on posterior part of carapace at midway between cervical groove and posterior carapace margin; posterior part with shoulder along cervical groove bearing 1 small spine; cervical groove extending to anterolateral notch; branchiostegite poorly calcified.

Pleon ( Fig. 1B View FIGURE 1 ) flattened dorsoventrally. Pleuron 1 narrow, demarcated from tergum by distinct longitudinal groove, posteroventral angle rounded; pleuron 2 asymmetrical, anterior part demarcated from tergum by distinct longitudinal groove reaching to midlength of somite, ventral margin slightly upturned. Pleomeres 3–5 each with short curved groove on anterior part; pleural margins with row of seta directed laterally, each posterolateral margin rounded. Pleomere 6 ( Fig. 2C View FIGURE 2 ) longest, 1.2 times as wide as long (greatest width at 0.7 length of somite); lateral margins parallel in anterior half, each with low convexity posterior to midlength, and then narrowing posteriorly; posterior margin nearly straight, smooth, with small notch on each lateral part. Telson ( Fig. 2D View FIGURE 2 ) subrectangular, 1.1 times as wide as long (greatest width at anterior 0.3); dorsal surface with blunt longitudinal ridges laterally, proximal part slightly elevated, though not forming distinct transverse carina; lateral margins slightly converging in posterior 0.7, unarmed; posterior margin bilobed with distinct median notch, fringed with fine long setae.

Ocular peduncle ( Fig. 2A View FIGURE 2 ) moderately stout, subcylindrical, unarmed, reaching midlength of rostrum, widened basally; cornea terminal, moderately large, lightly pigmented, corneal width subequal to diameter of eyestalk.

Antennular peduncle ( Fig. 2A, E View FIGURE 2 ) reaching distal margin of antennal peduncle article 4. Article 1 subequal in length to distal 2 articles combined, with prominent ventrodistal spine directed anteriorly; statocyst lobe slightly inflated. Article 2 shortest, cup-like. Article 3 slightly widened distally, unarmed. Upper flagellum shorter than peduncle consisting of 15–17 articles; lower flagellum much slenderer than upper flagellum.

Antennal peduncle ( Fig. 2A View FIGURE 2 ) with article 1 unarmed. Articles 2 with faintly granulate on dorsolateral margin proximally. Article 3 armed with 2 or 3 widely spaced spines on ventral margin. Article 4 with 2 or 3 spines on ventral margin, increasing in size distally. Article 5 less than half-length of article 4, unarmed. Scaphocerite clearly demarcated basally, with 2 unequal spines dorsodistally. Flagellum about twice as long as carapace, each article with thin setae of various length.

Mouthparts not dissected, though external observation made. Mandible without prominent tooth on mesial margin of incisor process. Maxillule and maxilla without distinctive features. Maxilliped 1 without epipod. Maxilliped 2 without distinctive features. Maxilliped 3 ( Fig. 3A View FIGURE 3 ) with endopod moderately stout, extending as far as distal end of antennal peduncle; ischium to dactylus with thick long setae on lower margins; ischium with 2 tiny proximal spines on mesial face; merus to propodus unarmed; dactylus nearly straight, slightly shorter than propodus, terminating in blunt tip; exopod slender, not reaching upper distal margin of ischium, flagellum consisting of 3 articles, with long terminal setae; epipod small, leaf-like.

Pereopod 1 ( Figs. 3B View FIGURE 3 , 4 View FIGURE 4 A–D) moderately robust, subchelate; setation typical of upogebiids. Coxa with 1 conspicuous pro-curved spine on ventral surface. Ischium with 1 small, recurved spine on lower margin. Merus with row of 6 or 7 evenly spaced, small, erect spines in proximal 0.6 of lower margin; upper margin nearly straight, armed with 1 subdistal spine. Carpus cup-shaped, widened distally, slightly more than half-length of palm; upper surface with spines of various size, arranged in 3 irregular rows (distomesial spine strongest); upper lateral surface with shallow longitudinal sulcus, lower lateral margin sharply carinate; mesial face with few small spines, upper mesial margin with 2 prominent, elongate spines; lower distal angle also with 1 small spine. Carpus-propodus articulation with clockwise torsion of about 20° from perpendicular in right side, vice versa in left side. Palm about 3.2 times as long as high; upper margin with row of 12–15 strong, slender spines of subequal size and sparse moderately long setae over entire length (distalmost spine subterminal); dactylar condyle on lateral face little developed; mesial face with numerous small to moderately strong spines arranged in 4 longitudinal rows; lower margin gently concave, with 2 prominent strong spines proximal to base of fixed finger (of two spines, proximal spine, located at midlength of palm, distinctly shorter than distal spine); fixed finger distinctly shorter than dactylus, slightly curved, occlusal margin unarmed; 1 small spine just superior to base of fixed finger on lateral side. Dactylus about half length of palm, nearly straight but with slightly arcuate upper margin, terminating in minute corneous claw; upper (extensor) margin bearing 5 minute denticles and row of numerous setae increasing in length proximally; lateral face with longitudinal carina adjacent to upper margin and 2 rows of setae along midline; mesial face with double row of setae superior to midline; occlusal margin carinate in proximal 0.7, terminating distally in minute denticle, distal 0.3 rounded.

Pereopods 2–5 relatively slender; setation typical of genus (omitted in figures). Pereopod 2 ( Fig. 3C View FIGURE 3 ) reaching base of dactylus of pereopod 1; coxa bearing some spinules, arranged in single row, on ventromesial face ( Fig. 3B View FIGURE 3 ); ischium unarmed; merus with small subdistal spine on upper margin, unarmed on lower margin; carpus slightly widened distally, upper margin with row of 6 small spines on distal 0.6 and 1 small subterminal spine on lower margin; propodus elongate subrectangular, subequal in length to carpus, narrowing distally, upper margin with 1 small proximal spine, lower proximal margin angular; dactylus tapering to minute corneous tip, about 0.7 times as long as propodus, lateral surface with naked median area flanked by dense setal fields, mesial face with 2 rows of stiff setae flanking midline. Pereopod 3 ( Fig. 3D View FIGURE 3 ) with coxa bearing several scattered spinules on ventromesial face anterior to gonopore ( Fig. 4B View FIGURE 4 ); ischium unarmed; merus with 1 small upper distal spine and row of 6 small spines, widely spaced, on lower margin; carpus widened distally, upper margin with 2 tiny spines adjacent to midlength, lower margin with 1 tiny distal spine; propodus shorter than carpus, with gently convex upper margin; dactylus ( Fig. 3E View FIGURE 3 ) slightly longer than propodus, slightly recurved distally, terminating in acute tip, lower (flexor) margin slightly sinuous, with row of about 10 minute spiniform setae distal to midlength. Pereopod 4 ( Fig. 3F View FIGURE 3 ) with coxa unarmed; merus to propodus unarmed; carpus cup-shaped; propodus slightly longer than carpus, with gently arcuate upper margin; dactylus ( Fig. 3G View FIGURE 3 ) longer than propodus, faintly recurved distally, terminating in acute tip, lower (flexor) margin slightly sinuous, with row of 8 minute spiniform setae in distal 0.3. Pereopod 5 ( Fig. 3H, I View FIGURE 3 ) subchelate, articles unarmed; no trace of gonopore on coxa; carpus subequal in length to merus and propodus; propodus slightly arcuate, with short fixed finger; dactylus curved, terminating in blunt tip.

Arthrobranchs of type C (cf. Ngoc-Ho 1981), composed of deeply divided, narrow lamellae on either side of rachis.

Pleopod 1 ( Fig. 1B View FIGURE 1 ) of 2 articles. Pleopods 2–5 similar; endopods small and slender, less than 0.3 length of respective exopod; exopods relatively slender ( Fig. 2F View FIGURE 2 ).

Uropod ( Fig. 2G View FIGURE 2 ) with both endopod and exopod reaching posterior margin of telson. Protopod with small spine on posterior margin. Endopod subtrapezoidal with rounded distomesial angle and somewhat produced, rounded distolateral margin, 1.2 times as long as wide; inner margin nearly straight, outer margin also nearly straight, with small knob-like tubercle proximally; dorsal surface with median carina. Exopod widened distally, subtriangular, 1.5 times as long as wide, slightly exceeding beyond endopod, distal margin roundly truncate; upper surface with 2 longitudinal carina.

Eggs 0.9 x 1.0 mm in non-eyed stage.

Coloration in life. Body generally orange-brown, cervical groove on carapace and sulci on pleon showing as white lines; rostrum whitish. Pereopod 1 dorsally orange, ventrally whitish; pereopods 2–4 generally whitish, with tinge of orange-brown on upper distal parts of meri; pereopod 5 entirely white; eggs orange-yellow ( Fig. 5 View FIGURE 5 ).

Remarks. Gebiacantha acanthochela was originally described on the basis of a female holotype and two paratypes (one male and one ovigerous female) by Sakai (1967; as Upogebia ). In his descriptive text, Sakai (1967: 45) indicated the type locality as “Yellow Sea”, but the given position for one of the paratypes (29°02'N, 125°25'E) is actually in the East China Sea (about 370 km west of Amami-ohshima Island) ( Itani 2004). Actually, in the Japanese summary of the same article, Sakai (1967: 39) stated that the collection locality was in the East China Sea. Sakai (2006) listed two additional specimens (as Upogebia ), but the locality was indicated as “probably Yellow Sea”; no detailed accounts or comments on those additional specimens were provided.

The present specimens agree with the original description of G. acanthochela except for a few minor details: spinules on the anterolateral margin of the carapace are four to six in the present specimens, whereas there are seven or eight spinules on that margin in the type material; dorsolateral margin of antennal peduncle article 2 only minutely granulate in the present specimens (versus having few spinules proximally; Sakai 1967: pl. 4, fig. B).

Species of Gebiacantha can be divided into two groups on account of the shape of the uropodal exopod (cf. Ngoc-Ho 1989, 1994a). Those characterised by a distally widened, subtriangular uropodal exopod (with a subtrun-cate distal margin) include G. acanthochela , G. albengai , G. arabica , G. dampieri , G. fortispinata n. sp., G. lifuensis , G. monoceros , G. multispinosa , G. plantae , G. poorei , G. priochela and G. talismani (cf. Ngoc-Ho 1989, 1994b, 2005, 2008). Those characterized by an oval-shaped uropodal exopod include G. acutispina , G. bermudensis , G. ceratophora , G. lagonensis , G. laurentae , G. reunionensis , G. richeri , and G. sagamiensis (cf. Ngoc-Ho 1989, 1994a, 1994b; Williams 1993; Komai 2017). Dworschak (2019) has reported variation in the number and size of the rostral ventral spines of G. laurentae and in armature on the antennal peduncle lower margin of G. multispinosa . The present study demonstrates a wider variation in the number of anterolateral spinules of the carapace in G. acanthochela . These variations diminish significance of some of the key characters employed in the identification keys of Ngoc-Ho (1989, 1994b).

Gebiacantha acanthochela seems to differ from all but G. fortispinata n. sp. and G. multispinosa in having more than 20 spines, arranged in three or four rows, on the mesial face of the female cheliped palm. In G. monoceros and G. albengai , the mesial face of the female pereopod 1 palm is unarmed ( Ngoc-Ho 1989, 2005); in the other nine species, there are fewer than 20 spines arranged in two or three rows ( Ngoc-Ho 1989, 1994a, 1994b, 2008; this study). Spines on the upper margin of the female pereopod 1 palm are generally more numerous in G. acanthochela than in other allied species, except for G. fortispinata n. sp., G. multispinosa and G. plantae (there are 11 or more spines versus 10 or less) ( Ngoc-Ho 1989, 1994a, 1994b, 2003, 2005, 2008). The two or three relatively small rostral ventral spines, clustered in the distal 0.2 of the rostrum, may distinguish G. acanthochela from the other 12 allied species. In G. albengai , G. arabica , and G. monoceros , the rostrum has only one ventral spine subterminally (in G. arabica , minute additional denticles may be present; see Ngoc-Ho 1989); in G. poorei , there are two ventral spines, both being much stronger than those of G. acanthochela , of which the posterior spine is located at the midlength of the rostrum (cf. Ngoc-Ho 1994a); in the other species, there are three or four moderately spaced ventral spines on the distal 0.3–0.5 of the ventral surface, and those spines are generally more pronounced than in G. acanthochela ( Ngoc-Ho 1989, 1994a, 1994b, 2003, 2008; this study). The proportionally narrower telson (1.1–1.2 times as long as wide) distinguishes G. acanthochela from G. lifuensis and G. multispinosa (1.5 times as long as wide; Ngoc-Ho 1994b). The rounded tip of the uropodal endopod distinguishes G. acanthochela from G. arabica , G. lifuensis , G. multispinosa , and G. plantae , in which the tip of the uropodal exopod is subacutely pointed ( Ngoc-Ho 1989, 1994a, 1994b).

Sakai (1982) synonymised G. acanthochela with G. ceratophora (as Upogebia ), but this synonymy was rejected by Ngoc-Ho (1989). Sakai (2006) recognised G. acanthochela as a valid species, although he continued to assign it to Upogebia .