Amakusaxius amakusanus (Miyake & Sakai, 1967)

Komai, Tomoyuki, Chan, Tin-Yam & Shy, Jhy-Yun, 2013, A redescription of a rare axiid shrimp, Amakusaxius amakusanus (Miyake & Sakai, 1967) (Crustacea: Decapoda: Axiidea) from new material collected off Taiwan, Zootaxa 3669 (4), pp. 490-502 : 492-501

publication ID	https://doi.org/ 10.11646/zootaxa.3669.4.4
publication LSID	lsid:zoobank.org:pub:7B3A771A-6DC5-48C5-867E-03A2B76369B3
DOI	https://doi.org/10.5281/zenodo.5697816
persistent identifier	https://treatment.plazi.org/id/03C32A02-1736-1E20-DBB1-F88AFD9AFD68
treatment provided by	Plazi
scientific name	Amakusaxius amakusanus (Miyake & Sakai, 1967)
status

Treatment

Amakusaxius amakusanus (Miyake & Sakai, 1967) View in CoL

( Figs 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Calocaris (Calastacus) amakusana Miyake & Sakai, 1967: 306 , fig. 2, pl. 4B. Axiopsis (Axiopsis) amakusana .—Sakai 1987: 303 (list).

Acanthaxius amakusana .—Sakai & de Saint Laurent 1989: 73; Kensley 1996b: 71 (list).

Amakusaxius amakusanus .—Sakai 2011: 45.

Material examined. Holotype: female (cl 9.4 mm), off Tomioka, Amakusa Island, Kyushu, Japan, 20–40 m, 22– 24 August 1956, coll. Sadayoshi Miyake, KMNH (formerly deposited at the Zoological Laboratory, Faculty of Agriculture, Kyushu University, registration number 4580).

Non-type: 1 male (cl 15.5 mm), 1 ovigerous female (cl 13.6 mm), Penghu Islands, Taiwan, commercial trawlers, about 50 m, 31 March 2011, NTOU A01349; same locality, April 2011, 1 male (cl 15.2 mm), 1 ovigerous females (cl 15.6 mm), NTOU A01350; same data, 1 ovigerous female (cl 13.4 mm), CBM-ZC 11570; same locality, January 2013, 1 male (cl 12.0 mm), NTOU AO 1351.

Redescription. Body moderately stout. Rostrum ( Figs 1 View FIGURE 1 A, B; 2A, B) 0.2 times distance between rostral base and cervical groove or 0.1 times as long as carapace, moderately widely triangular with acute tip in dorsal view; lateral margin with 1 or 2 (usually 2) small subacute spines and supraocular spine, not continuous with distinct lateral gastric carina on carapace. Carapace ( Figs 1 View FIGURE 1 A, B; 2A, B) fairly compressed laterally, sparsely granulate dorsally, nearly smooth or microscopically granulate laterally, with scattered short setae on dorsal surface; dorsal surface nearly straight, gastric region not sloping down to rostrum; gastric median carina distinct, extending beyond rostral base anteriorly and reaching cervical groove, with 6–9 small denticles or tubercles; submedian carinae divided into 4 short divisions, each terminating anteriorly in acute or subacute spine; lateral carinae divided into 2 unequal divisions, each terminating in acute to blunt spine; postcervical carina low, blunt; cervical groove deep, extending to pterygostomial region; suborbital margin broadly convex; pterygostomial margin broadly rounded.

Seventh thoracic sternite with shield ( Fig. 1 View FIGURE 1 C) divided into two sections by distinct transverse ridge; anterior section triangular, slightly depressed below; posterior section deeply divided by deep median groove, each lateral angle produced in blunt tooth directed ventrally. Precoxal plate on eighth thoracic sternite ( Fig. 1 View FIGURE 1 D) well calcified, divided into two unequal parts by oblique suture, bearing prominent, basally articulated process at anteroventral angle; posterior division of precoxal plate not expanded into prominent lobe.

First abdominal somite ( Figs 1 View FIGURE 1 E; 2C) with tergum bearing subrectangular plateau defined by shallow groove; pleuron triangular with blunt to acute ventral apex, lateral surface with distinct longitudinal carina posteriorly. Second pleuron ( Fig. 1 View FIGURE 1 E) asymmetrical; lateral surface shallowly depressed; ventral margin unarmed, rounded at either angle. Third to fifth pleura ( Fig. 1 View FIGURE 1 E) shallowly depressed; third pleuron rounded, unarmed (females) or armed with minute spine at anteroventral angle (male); fourth and fifth pleura ( Fig. 1 View FIGURE 1 E) each with minute spine at anteroventral angle (male and female holotype) or unarmed (ovigerous female), fourth pleuron bluntly angular, fifth pleuron subacutely (male) or bluntly (female) angular. Sixth pleuron ( Fig. 1 View FIGURE 1 E) acutely pointed ventrally, with truncate posterolateral projection. Telson ( Fig. 2 View FIGURE 2 D, E) subrectangular, approximately as long as broad; proximolateral part somewhat thickened, terminating in small marginal spine; lateral margin slightly converging posteriorly, bearing 1 or 2 small spines near posterolateral angle; posterior margin slightly convex, with small posteromedian spine, posterolateral area with 2 subequal, minute movable spines; dorsal face shallowly sulcate medially, submedian ridges each terminating posteriorly in small spine at anterior 0.4, dorsolateral ridges low, obsolete, each with 1 small spine located at about midlength of telson.

Eyestalk ( Fig. 2 View FIGURE 2 A, B) subcylindrical, exceeding beyond rostral apex by length of cornea; cornea distinctly shorter than eyestalk, slightly inflated, darkly pigmented. Antennular peduncle ( Fig. 2 View FIGURE 2 A, B) extending as far as antennal peduncle; statocyst lobe on first segment unarmed; flagella more than twice longer than carapace. Antennal peduncle ( Figs 1 View FIGURE 1 F; 2B) with first segment bearing 1 prominent spine on ventrolateral distal angle and 1 or 2 spinules on ventrodistal margin; second segment with dorsolateral distal spine curved inward and overreaching distal margin of third segment; scaphocerite acuminate, gently curved, reaching midlength of fourth segment; third segment with 3 spines, increasing in size distally, on ventromesial margin; fourth and fifth segments stout, cylindrical, combined length subequal to second segment; flagellum missing.

Third maxilliped ( Fig. 3 View FIGURE 3 A) moderately slender, overreaching antennal peduncle by length of distal two segments. Coxa with ventrodistal spine. Basis with 1 prominent spine ventrodistally. Ischium with sharp carina on lateral surface dorsally; crista dentata well developed, bearing about 15 slender spines (proximal spines noticeably decreasing in size proximally), distal prolongation curved mesially, reaching proximal 0.2 of merus ( Fig. 5 View FIGURE 5 A); ventral margin with 2 small spines in proximal half. Merus with 4 ventral spines increasing in size distally. Carpus with 1 small spine at ventrolateral distal angle. Dactylus 0.7 times as long as propodus. Exopod overreaching distal margin of merus.

Chelipeds ( Fig. 4 View FIGURE 4 A–D) slightly unequal and greatly dissimilar. Major cheliped ( Fig. 4 View FIGURE 4 A, B) with coxa bearing 2 small spines on mesial margin. Basis with 1 tiny tubercle on ventral margin proximally. Ischium with 3–6 main tubercles on ventral margin becoming stronger and more acute distally. Merus with dorsal margin fairly sinuous, non-carinate, with 1 small subterminal spine; lateral surface with 2 subterminal spines aligned to dorsal spine and some tiny tubercles bearing tuft of stiff setae around subterminal spines, otherwise nearly smooth, with scattered very short setae, ventrodistal part forming shallow excavation to receive proximoventral part of carpus, ventrolateral distal angle with spine-like tubercle; mesial face nearly smooth; ventrolateral margin unarmed, ventromesial margin with row of 6 or 7 small spines or tubercles. Carpus much higher than long; dorsal surface with 1 or 2 main spines mesially, followed by some small tubercles; lateral surface with scattered tufts of short stiff setae and some rounded tubercles dorsally, ventrolateral distal angle with small spine; mesial surface with scattered tufts of short setae; ventral surface with 1 small spine mesially. Chela massive, 2.4 times longer than high; ventral margin slightly sinuous; broad hiatus between fingers in proximal half. Palm 1.1–1.2 times longer than high, dorsal surface non-carinate, bearing 4 or 5 small spines or tubercles and scattered small rounded tubercles, these armature partially obscured by tufts of stiff setae arising from distal base of each tubercle; lateral face convex, covered with numerous rounded tubercles of various sizes, each tubercle bearing tuft of stiff setae on distal side (some tubercles adjacent to dorsal margin somewhat enlarged, subconical; 1 subterminal tubercle proximal to base of dactylus larger than others, spine-like); ventral surface forming broad, tuberculate ridge, becoming more clearly delimited distally on fixed finger, tubercles bordering ventral ridge sometimes acute, spine-like; mesial face also with numerous tubercles of various sizes, some tubercles proximal to base of dactylus somewhat enlarged. Fixed finger with tufts of short to long setae on surfaces; blunt but distinct median carina on each lateral and mesial surfaces, extending onto base of dactylus, each carina bearing some prominent tubercles proximally; cutting edge with row of molar-like calcareous teeth. Dactylus slightly curved, 1.1 times longer than palm, tapering distally to blunt calcareous apex, with numerous tufts of short to long stiff setae on lateral and mesial surfaces; dorsal margin with 2 spines in proximal 0.8 and sharply defined keel in distal 0.8; lateral surface with median carina becoming obsolete distally and bearing 4 rounded tubercles proximally; mesial surface also with median carina becoming obsolete distally and bearing 6 rounded tubercles proximally; cutting edge with molar-like calcareous teeth.

Minor cheliped ( Fig. 4 View FIGURE 4 C, D) much slenderer than major cheliped. Coxa bearing 2 small spines on mesial margin. Basis smooth on ventral margin proximally. Ischium with 5–7 small spines or tubercles on ventral margin increasing in size distally. Merus with dorsal margin gently sinuous, non-carinate, with 2 small spines in distal 0.3; lateral surface with 2 subterminal spines aligned to ultimate spine on dorsal margin, and some setae-bearing tubercles inferior to dorsal subterminal spines, ventrodistal part forming shallow excavation to receive proximoventral part of carpus, ventrolateral distal angle directed ventrally and terminating in acute spine; mesial face nearly smooth; ventral margin armed with row of 7 small spines increasing in size distally. Carpus higher than long; dorsal surface with 2 prominent spines mesially; lateral surface with scattered tufts of short stiff setae, ventrolateral distal angle with small submarginal spine; mesial surface with scattered tufts of short setae; ventral surface with 1 spine located distal to midlength. Chela elongate, 3.9 times longer than high; ventral margin nearly straight; narrow hiatus between fingers over entire length. Palm slightly becoming higher distally, 1.2 times longer than high, dorsal surface non-carinate, bearing 4 prominent, equidistant spines and short to long setae; lateral face gently convex, with scattered tufts of stiff setae, longitudinal row of 4 spines proximal to base of dactylus and row of 4 prominent, forwardly directed spines adjacent to ventral margin; mesial surface also gently convex, with numerous scattered tufts of short to long setae and 1 small spine proximal to base of dactylus; ventral surface forming broad ridge becoming more distinct on fixed finger. Fixed finger with tufts of short to long setae on surfaces, in particular, those adjacent to cutting edge obscuring armature; cutting edge with row of small teeth becoming obsolescent distally; tip normally acuminate. Dactylus nearly straight, only slightly curved near tip, 2.4– 2.5 times longer than palm, with numerous tufts of short to long stiff setae on lateral and mesial surfaces; dorsal margin non-carinate, with 2 or 3 prominent spines in proximal 0.5–0.6; cutting edge with row of small acute teeth in proximal 0.6 and faintly to microscopically denticulate in distal 0.4; tip normally acuminate.

Second pereiopod ( Fig. 3 View FIGURE 3 B) overreaching antennal peduncle by half length of chela. Coxa unarmed, with shallow concavity on mesial face. Ischium with small ventrodistal spine. Merus with 3 small spines on ventral margin, increasing in size distally. Carpus 0.9 times as long as chela; ventrodistal angle somewhat produced. Palm becoming slightly higher distally. Fingers each with row of minute corneous spinules on cutting edge; dactylus about 1.4 times longer than palm.

Third pereiopod ( Fig. 3 View FIGURE 3 C) overreaching antennal peduncle by length of dactylus. Coxa with mesial face slightly concave. Ischium unarmed. Merus with 3 spines on ventral margin, increasing in size distally. Carpus unarmed. Propodus with 6 or 7 transverse sets of corneous spinules on lateral surface ventrally (spines becoming longer ventrally), including one on ventrodistal margin; lateral surface distally with additional 3 sets of corneous spinules superior to midline. Dactylus ( Fig. 5 View FIGURE 5 D) half-length of propodus, gently curving, terminating in corneous claw, with tufts of stiff setae on surfaces; lateral surface with row of 5 or 6 corneous spinules increasing in size distally; mesial surface unarmed; ventral (flexor) margin with row of minute corneous spinules in distal half.

Fourth pereiopod ( Fig. 3 View FIGURE 3 D) slightly overreaching antennal peduncle by half-length of dactylus. Coxa with minute denticle on mesial surface. Ischium unarmed. Merus with 3 spines on ventral margin, increasing in size distally. Carpus unarmed. Propodus with 7 or 8 transverse sets of corneous spinules on lateral surface ventrally (including that on ventrodistal margin); lateral surface with additional 3 or 4 sets of corneous spinules in distal half; no development of grooming apparatus. Dactylus ( Fig. 5 View FIGURE 5 E) about 0.4 times as long as propodus, tapering distally to corneous claw, gently curving; lateral surface with row of 7 or 8 corneous spinules increasing in size distally; mesial face unarmed; ventral (flexor) margin with row of minute corneous spinules laterally.

Fifth pereiopod ( Figs 3 View FIGURE 3 E; 5F) semichelate with distinctly developed ventrodistal process on propodus opposed to dactylus. All segments without conspicuous spines. Propodus with obliquely longitudinal line of grooming setae distally on lateral surface ( Fig. 5 View FIGURE 5 G); mesial face with 2 or 3 transverse sets of corneous spinules distally, ultimate set located at base of fixed finger; fixed finger rounded, margins bordered by microscopic corneous spinules. Dactylus ( Fig. 5 View FIGURE 5 G) lanceolate, terminating in corneous claw; outer margin somewhat expanded proximally; flexor surface excavated proximally; inner margin with row of minute corneous spinules. Well developed gonopores present.

Gill formula summarized in Table 1 View TABLE 1 . Podobranchs on third maxilliped to third pereiopod prominent, but devoid of lamellae.

Maxillipeds Pereiopods First pleopod absent in males; female first pleopod uniramous, 2-articulated, protopod about 0.3 length of ramus. Second to fifth pleopods moderately narrow, each with well-developed appendix interna. Appendix masculina on second pleopod slightly longer than appendix interna, rod-like, with numerous setae on apex to dorsal margin ( Fig. 2 View FIGURE 2 F).

Uropod ( Fig. 2 View FIGURE 2 G) with protopod subtriangular, with deep notch on posterior margin to accommodate proximodorsal knob of exopod. Endopod narrow; lateral margin slightly concave, with distinctly delimited proximal angle; mesial margin gently convex, with peak proximal to midlength, bearing row of minute corneous spinules; lateral carina on dorsal surface distinct, with 2 prominent spines in posterior half and produced posterolaterally in strong spine; middorsal carina also distinctly delimited, with 4 or 5 prominent spines, including posterior marginal one. Exopod exceeding beyond endopod; lateral margin convex, with 5 or 6 prominent spines and sometimes interspersing spinules; mesial margin slightly convex, with row of minute corneous, movable spinules in posterior half; distal suture oblique, bearing 5 spines increasing in size mesially; movable spine just lateral to terminal flap very strong, slightly curved laterally; terminal flap small, subsemicircular; dorsolateral carina with 4 or 5 prominent spines; middorsal carina arcuate, unarmed, terminating posteriorly in spine in series on distal suture; proximodorsal knob terminating in spine.

Coloration. Body generally reddish pink ( Fig. 6 View FIGURE 6 ). Dorsal carapace mostly yellowish. Abdomen with dorsal surface with mosaic of white and reddish pink color, ventral margin of pleura with thick white bands, hinges between somites and spines on tail fan somewhat whitish. Eyes blackish brown. Antennular and antennal flagella pale yellowish. First pereiopods with chelae and carpi dorsally orangish and ventrally pale pink to whitish on lateral side and pale yellowish on mesial side, proximal segments reddish pink. Posterior pereiopods reddish pink with hinges somewhat pale colored. Eggs orangish.

Distribution. Japan and Taiwan; at depths of 20– 50 m.

Remarks. The holotype female is still in good condition, though the right major cheliped is missing, as Miyake & Sakai (1967) mentioned. Although the six specimens from Taiwan are all larger than the holotype, they agree well with the latter and there is little doubt that they are conspecific.

The gill formula reexamined is different from that of Miyake & Sakai (1967: 307), but the discrepancy is due to the different interpretation of the structure of the epipods and podobranchs on the third maxilliped and pereiopods. Miyake & Sakai (1967) counted the numbers of epipods on each third maxilliped to third pereiopods as two, but this is an error. The anterior branches on those epipods actually represent podobranchs devoid of gill lamellae (e.g., Poore 1994; Komai 2000).