Formosaxius
Creators: name: Lin, Tomoyuki Komai Feng-Jiau
name: Chan, Tin-Yam
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Axiidae
Formosaxius

description: Formosaxius dorsum n. sp.
(Figs. 1–3, 13A, B)
Type material. Holotype: female (cl ca. 12.0 mm), TAIWAN 2005, stn CP 290, 8 August 2005, 24o57.301’N, 122 o5.030’E, 249–255 m, (NTOU A01087).
Paratype: female (cl 12.6 mm), TAIWAN 2001, stn CP 95, 18 May 2001, 24°55.80’N, 122°5.73’E, 269– 360 m (NTOU A00023).
Description of holotype. Dorsum of carapace damaged in posterior part, left cheliped, right second, left third, right fourth and both fifth pereopods missing. Rostrum (Fig. 1 A, B) 0.3 times of distance between rostral base and cervical groove, triangular with acute tip in dorsal view; lateral margin with 4 small spines anterior to rostral base, continuous with distinct, unarmed lateral gastric carina on carapace; dorsal surface shallowly concave. Carapace (Fig. 1 A, B) nearly smooth on surface; dorsal surface weakly convex, gastric region sloping down to rostrum; no clearly differentiated supraocular spine; median gastric carina distinct, reaching to cervical groove, with 2 small spines anteriorly and 1 obtuse convexity anterior to midway between rostral base and cervical groove; submedian carina consisting of longitudinal row of 6 small spines and 2 minute tubercles (left) or 7 small spines (right); lateral gastric carina extending beyond midway between rostral base and cervical groove; blunt postcervical carina apparent at least in posterior part (Fig. 1 C); cervical groove distinct, extending to pterygostomial region; pterygostomial margin rounded.
Seventh thoracic sternite with thoracic shield (Fig. 1 D) deeply divided in midline over posterior twothirds and slightly produced anteriorly in obtuse apex. Eighth sternite (not figured) with setose semicircular flap on anterior face at base of leg.
First abdominal pleuron (Fig. 1 E) shallowly depressed on lateral surface with slightly upturned posterior margin, ventral margin rounded. Second pleuron asymmetrical (i.e., anterior and posterior parts unequal); lateral surface with fairly deep longitudinal depression accompanied dorsally with blunt ridge; ventral margin unarmed, rounded at either angle. Third and fourth pleura each with shallow depression on lateral surface, ventral margin rounded. Fifth pleuron also with shallow depression on lateral surface, ventral margin rounded. Sixth pleuron broadly rounded ventrally, with rounded posterolateral projection. Telson (Fig. 1 F) 1.4 times as long as broad, lateral margin with 4 minute spines, posterior margin convex, without posteromedian spine, posterolateral angle with 2 minute, marginal spiniform setae; dorsal face shallowly sulcate medially, left dorsolateral ridge unarmed, right dorsolateral ridge with 2 spines in posterior one-third.
Eyestalk (Fig. 1 A, B) about 0.8 length of rostrum; cornea shorter than eyestalk, darkly pigmented. Antennular peduncle (Fig. 1 A, B) reaching midlength of fourth segment of antennal peduncle; statocyst lobe on first segment with distal spine. Antennal peduncle (Fig. 1 A, B) with first segment bearing 2 spinules at ventromesial distal angle and 1 slender spine on ventrodistal margin; second segment with straight dorsolateral distal spine reaching nearly midlength of scaphocerite; scaphocerite simple, straight, reaching midlength of fourth segment; third segment with 1 prominent spine at distomesial angle; fourth segment slightly longer than second segment; fifth segment less than half length of fourth segment.
Third maxilliped (Fig. 2 A) moderately slender; basis with 1 spine distomesially; crista dentata on ischium with 17 corneous-tipped teeth increasing in size distally; merus with 3 spines on ventral margin (distal spine largest); carpus with 1 small distal spine on ventral margin; propodus slightly tapering distally; exopod slightly overreaching distal margin of first segment of antennal peduncle.
Only right cheliped remaining (Fig. 2 C). Coxa with 2 ventromesial spines. Basis unarmed. Ischium with 3 spines on ventral margin (proximal one minute); merus with dorsal margin sinuous, sharply carinate, with 1 small spine subdistally, lower margin with row of 5 spines in proximal 0.7, lateral and mesial faces smooth. Carpus 1.1 times longer than high, dorsal margin smooth, ventral margin also unarmed, lateral and mesial faces smooth. Palm 1.1 times longer than high, dorsal margin slightly concave, sharply carinate, with 1 small subdistal spine (Fig. 2 D), ventral margin (including fixed finger) slightly sinuous; lateral face slightly convex, nearly smooth, with tufts of long stiff setae adjacent to dorsal and ventral margins and at base of dactylus, sharply carinate along ventral margin. Fixed finger 1.3 times longer than palm; lateral surface faintly elevated in midline, with row of tufts of long setae adjacent to cutting edge; cutting edge slightly sinuous, with row of minute corneous spinules (Fig. 2 E). Dactylus weakly curved, crossing with fixed finger at tip when closed, with numerous tufts of long stiff setae on lateral and mesial faces; both lateral and mesial faces slightly elevated in midline as blunt ridge in proximal half; dorsal margin unarmed; cutting edge without conspicuous teeth, but with row of minute corneous spinules.
Second pereopod (Fig. 2 F) moderately slender; ischium unarmed; merus with 3 ventral spine; carpus slightly shorter than chela; fingers subequal in length to palm, each with row of minute corneous spinules on cutting edge. Third pereopod (Fig. 2 G) unarmed; propodus with sparse setae; dactylus (Fig. 2 H, I; tip broken off) subconical, slightly twisted, lateral surface with row of tufts of setae on midline and ventrally with thick covering of setae, mesial face also with few tufts of setae. Fourth pereopod (Fig. 2 J) moderately slender; propodus with grooming apparatus consisting of thick cluster of setae and several stout, setulose setae located subdistally (Fig. 2 K, L); dactylus (Fig. 2 K, L) about 0.4 times as long as propodus, subconical, slightly twisted, lateral surface with 4 long, slender spiniform setae along extensor margin, obscured by thick long setae.
First pleopod uniramous, two-segmented, ramus flexible, longer than protopod. Second to fifth pleopods moderately narrow, each with well-developed appendix interna (Fig. 1 G).
Uropodal endopod (Fig. 1 H) 1.5 times as long as wide, with 1 lateral spine at posterolateral position; longitudinal ridge on dorsal surface with row of 8 (left) or 7 (right) spines. Uropodal exopod (Fig. 1 H) with straight, unarmed lateral margin, posterolateral angle with 1 tiny spine; dorsal ridge unarmed; transverse suture with row of minute spinules.
Note on paratype. Both chelipeds, left third to fifth pereopods missing. Rostrum (Fig. 3 A, B) 0.17 times as long as carapace and 0.3 times of distance between rostral base and cervical groove, with 3 lateral spines. Carapace (Fig. 3 A, B) with median gastric carina with 2 small spines anteriorly and 1 very low convexity anterior to midway between rostral base and cervical groove; submedian carina consisting of longitudinal row of 5 small spines and 3 tiny tubercles (left) or 7 small spines (right). Telson with lateral margin unarmed, posterolateral angle with 2 subequal, minute spiniform setae; dorsal face with 2 pairs of small spines medially, anterior pair on submedian ridges and posterior pair on dorsolateral ridges. Eyestalk about half length of rostrum; cornea shorter than eyestalk, darkly pigmented. Antennal peduncle (Fig. 3 B) with scaphocerite far overreaching midlength of fourth segment. Third maxilliped moderately slender; basis with 1 spine distomesially; ischium with 2 minute denticles on ventral margin; merus with 3 spines on ventral margin increasing in size distally; carpus unarmed on ventral margin. Second pereopod with merus unarmed (left) or armed with 1 ventral spine arising slightly distal to midlength. Fifth pereopod (Fig. 3 C) more slender than third and fourth pereopods; propodus with grooming apparatus consisting of short transverse rows of stiff setae, ventrodistal projection bearing terminal cluster of 4 spiniform setae; dactylus lanceolate, outer surface slightly excavate. Uropodal endopod unarmed on lateral margin, middorsal ridge with row of 6 spinules (left) or unarmed (right).
Coloration. Body (Fig. 13A, B) generally pinkish brown (holotype) to pale brown (paratype), ventral parts and appendages lighter in color; corneas dark brown.
Distribution. Known only from northeastern Taiwan, 249–360 m deep.
Remarks. As is apparent from the above description, variations are observed in the armament of various body structures, including the rostrum, gastric submedian carinae, telson, third maxilliped, chelipeds, second pereopods, and uropods, and the length of the scaphocerite.
Etymology. The name “ dorsum ” alludes to the distinct middorsal carina on the posterior 0.2 of the carapace in the new species. Used as a noun in apposition.
description: Published as part of Lin, Tomoyuki Komai Feng-Jiau & Chan, Tin-Yam, 2010, Five new species of Axiidae (Crustacea: Decapoda: Axiidea) from deep-water off Taiwan, with description of a new genus, pp. 1-28 in Zootaxa 2352 on pages 3-8, DOI: 10.5281/zenodo.193489