Axianassa ngochoae, Anker, 2010

Anker, Arthur, 2010, The mud-shrimp genus Axianassa Schmitt, 1924 (Crustacea, Decapoda, Axianassidae) in the Indo-West Pacific, with description of a new species from French Polynesia, Zootaxa 2557 (1), pp. 49-59 : 50-58

publication ID	https://doi.org/ 10.11646/zootaxa.2557.1.5
DOI	https://doi.org/10.5281/zenodo.5308750
persistent identifier	https://treatment.plazi.org/id/E34F87C2-8024-9813-FF1A-FE8CE0EF329B
treatment provided by	Felipe
scientific name	Axianassa ngochoae
status	sp. nov.

Treatment

Axianassa ngochoae n. sp.

( Figs. 1–8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

Type material. Holotype, male, CL 6.7 mm ( FLMNH UF Arthropoda 23329), French Polynesia, Society Islands , Moorea, Pihaena, lagoon, near shore, muddy bottom near living and dead coral heads, depth: 0.3–1 m, bait suction (yabby) pump, coll. A. Anker, 21 October 2009 [fcn BMOO-06380] . Paratypes: 1 female, CL 8.7 mm ( FLMNH UF Arthropoda 23328), same collection data as for holotype [fcn BMOO-06377] ; 1 female, CL 5.3 mm (MNHN-Th 1572), same collection data as for holotype [fcn BMOO-06381] ; 1 male, CL 6.8 mm ( FLMNH UF Arthropoda 23330), French Polynesia, Society Islands , Moorea, Pihaena, lagoon, near shore, muddy bottom near living and dead coral heads, depth: 0.5–1 m, bait suction (yabby) pump, coll. A. Anker and V. Liao, 18 November 2009 [BMOO-09173] .

Description. Carapace with straight linea thalassinica and well-defined, crescent-shaped cervical groove ( Fig. 1a View FIGURE 1 ; see also Fig. 7a View FIGURE 7 , 8a View FIGURE 8 ); branchiostegial margin somewhat elevated; pterygostomial region rounded, not conspicuously protruding, fringed with setae; dorsal surface carapace with long, stiff, irregularly scattered setae ( Fig. 1a, b View FIGURE 1 ). Rostrum broad at base, rounded, reaching slightly beyond anterior margin of eyestalks ( Fig. 1c, d View FIGURE 1 ). Abdomen thinly sclerotised, smooth; dorsal surface of tergites with long stiff setae; rows of long setae present along ventral margin of tergites of second to sixth somites ( Fig. 1a View FIGURE 1 ); first abdominal somite with pleuron produced ventrally into blunt process adjacent to first pleopod base in females ( Figs. 1a View FIGURE 1 , 7b View FIGURE 7 ), into strong acute process in males ( Figs. 6f View FIGURE 6 , 8b View FIGURE 8 ); posterior somites without dense lateral fringes of plumose setae. Telson broad, tapering posteriorly, posterior margin broadly rounded, without armature ( Fig. 6c View FIGURE 6 ).

Eyestalks rounded or with rounded anteromesial bump; cornea moderately large compared to eyestalk, in lateral-subterminal position ( Fig. 1d View FIGURE 1 , 6e View FIGURE 6 ), pigmented blackish in alcohol, white-yellowish on living individuals ( Figs. 7 View FIGURE 7 , 8 View FIGURE 8 ). Antennular peduncle with third article subcylindrical, slender, reaching half-length of fourth article of antenna ( Fig. 1c View FIGURE 1 ); ventral flagellum about 3/5 length of dorsal flagellum. Antennal acicle dagger-like, relatively broad at base, tapering distally, not reaching mid-length of third article of antennular peduncle; fourth antennal article subcylindrical, elongate, robust, about twice as long as third article of antennular peduncle, with numerous long setae on lateral and ventrolateral surface ( Fig. 1b, c View FIGURE 1 ); flagellum well developed, reaching well beyond chelipeds.

Mouthparts typical for genus (cf. Kensley & Heard 1990, fig. 2D-I; Rodrigues & Shimizu 1992, figs. 4– 8). Mandible with triarticulated palp; molar and incisor processes partly fused; molar edge with nine smaller blunt teeth; incisor edge with five larger and one smaller acute teeth ( Fig. 2a View FIGURE 2 ). Maxillule with bisegmented palp, coxal and basal endites very setose ( Fig. 2b View FIGURE 2 ). Maxilla with undivided endopod; scaphognathite very broad, with five long, flexible setae on ventral (= posterior or near-basal) margin ( Fig. 2c View FIGURE 2 ). First maxilliped with broad, paddle-shaped endopod; exopod tri-segmented, basal segment broad, paddle-shaped [exopod missing on right side in dissected specimen, probably damaged during collection]; epipod and podobranch reduced to small rounded lobe; arthrobranch rudimentary ( Fig. 2d, e View FIGURE 2 ). Second maxilliped typical for genus, with elongate epipod bearing well-developed podobranch; endopod robust, with apical “head” formed by propodus and dactylus; exopod trisegmented ( Fig. 2f View FIGURE 2 ); two arthrobranchs. Third maxilliped ( Fig. 2g –k View FIGURE 2 ) pediform; epipod bifid, with well-developed podobranch; basis usually bearing one medium-sized, sharp tooth on distodorsal margin ( Fig. 2j View FIGURE 2 ); ischium with crista dentata bearing at least 17 teeth ( Fig. 2k View FIGURE 2 ); merus, carpus, propodus and dactylus with bands of fusiform setae mesially ( Fig. 2h View FIGURE 2 ) and with long setae along ventral margin and on dactylar apex ( Fig. 2g View FIGURE 2 ); two arthrobranchs.

First pereiopods (chelipeds) allometrically variable. Chelipeds of female paratype ( Fig. 3 View FIGURE 3 , 4 View FIGURE 4 ) stout, asymmetrical in shape, slightly unequal in size; major cheliped ( Fig. 3 View FIGURE 3 ) very robust; ischium with three sharp teeth on ventral margin, latter also bearing long setae ( Fig. 3a, d View FIGURE 3 ); merus inflated, with strongly convex dorsal and ventral margins, ventral margin with row of nine small teeth ( Fig. 3b, d View FIGURE 3 ); carpus cup-shaped, unarmed; chela ovate, somewhat compressed laterally; palm with large area of minute granules near base of pollex on both mesial and lateral sides ( Fig. 3a–c View FIGURE 3 ); fingers about 3/5 length of palm, stout; tips nearly crossing; cutting edges armed with irregular blunt teeth ( Fig. 3c View FIGURE 3 ); ventral margin of palm and pollex and dorsal and lateral margin of dactylus fringed with numerous setae; minor cheliped ( Fig. 4 View FIGURE 4 ) slightly smaller and less robust than major cheliped; ischium with two strong teeth on ventral margin ( Fig. 4a, b View FIGURE 4 ); merus and carpus similar to those of major cheliped; chela distinctly more slender than in major cheliped, ovate; palm with small area of granules near pollex on both mesial and lateral side ( Fig. 4a–c View FIGURE 4 ); fingers about as long as palm, tips fully crossing; cutting edge of pollex armed with subtriangular, irregularly spaced teeth, including two conspicuously larger teeth ( Fig. 4c View FIGURE 4 ); cutting edge of dactylus with small rugosities only. Chelipeds of male holotype ( Fig. 6 View FIGURE 6 ) slightly asymmetrical, almost equal in size, both major ( Fig. 6g View FIGURE 6 ) and minor ( Fig. 6h View FIGURE 6 ) chelipeds overall more similar to minor cheliped of female (cf. Fig. 4 View FIGURE 4 ); major cheliped with ischium unarmed or armed with one sharp tooth; merus with about seven small teeth on ventral margin ( Fig. 6g View FIGURE 6 ); carpus cupshaped; chela smooth, without granulations; fingers close to 4/5 of palm length, with crossing tips, armed with subtriangular teeth as illustrated ( Fig. 6g View FIGURE 6 ); minor cheliped similar to major cheliped except for palm and fingers being somewhat more slender and fingers being as long as chela.

Second pereiopod pediform, robust; merus, carpus and propodus with long flexible setae along ventral margin ( Fig. 5a View FIGURE 5 ); dactylus less than half as long as propodus, simple, with crenulated ventral margin and numerous setae ( Fig. 5b View FIGURE 5 ). Third pereiopod robust, ischium, merus and carpus smooth, moderately setose; propodus with distoventral brushes of very stiff setae ( Fig. 5c View FIGURE 5 ); dactylus as long as propodus, somewhat sickle-shaped; dorsal margin bearing around nine stout corneous spines (some broken off); distoventral margin slightly expanded, carrying row of small spiniform setae ( Fig. 5d View FIGURE 5 ); distal portion of dactylus with tuft of stiff setae. Fourth pereiopod very similar to third pereiopod, slightly more slender ( Fig. 5e, f View FIGURE 5 ). Fifth pereiopod generally more slender than third and fourth pereiopods; propodus subchelate, ending in short fixed tooth (hidden among setae); distal 2/3 of propodus occupied by broad band of short stiff setae; dactylus less sickle-shaped, subspatulate ( Fig. 5g, h View FIGURE 5 ).

First female pleopod bisegmented, distal segment fringed with setae along margins ( Fig. 6d View FIGURE 6 ); first pleopod absent in males. Second to fifth pleopods similar, biramous, typical for genus. Uropods with broadly ovoid exopod and endopod ( Fig. 6a View FIGURE 6 ); lateral margin of exopod with four teeth, most-distal tooth largest ( Fig. 6b View FIGURE 6 ).

Gill/exopod formula as described for genus (see Kensley & Heard 1990).

Size. Medium-sized mud-shrimp, at CL 6.7–6.8 mm in males, 8.7 mm in female.

Colour in life. Male holotype and paratype uniform hyaline white, with yellowish to pinkish tinge, especially on chelipeds; eyes conspicuosly whitish-yellow; female paratype partly covered with thin reddish, possibly iron-containing coating ( Figs. 7 View FIGURE 7 , 8 View FIGURE 8 ).

Etymology. This new species is named after Dr. Nguyen Ngoc-Ho (MNHN), in recognition of her invaluable taxonomic work on Axiidea and Gebiidea.

Ecology. All specimens of A. ngochoae n. sp. were found in a near-shore, protected, somewhat muddy area of the Moorea lagoon, in burrows on mud or muddy sand bottom, not far from living and dead coral heads and large rocks, less than 1 m deep.

Taxonomic remarks. Axianassa ngochoae n. sp. differs from each of the other six species of Axianassa by at least two characters, for instance, from A. intermedia , A. jamaicensis , A. canalis and A australis by the absence of a mesial tooth on the antennal acicle; from A. intermedia and A. jamaicensis by the presence of a spiniform process on the first abdominal somite in males; from A. jamaicensis and A. australis by the less granulated chelipeds; specifically from A. intermedia by the less spinose ventral margin of the cheliped merus; from A. mineri by the elongate, non-bifid antennal acicle, the absence of a movable spine on the lateral margin of the uropodal exopod, and the absence of two sharp dorsal teeth on the uropodal endopod; from A. arenaria by the significantly shorter antennal acicle (not reaching mid-length of antennular peduncle), the ventrally rounded pleura of the second to fifth abdominal somites (vs. produced into a small tooth in A. arenaria ), the more faintly toothed lateral margin of the uropodal exopod, and the distinctly stouter chela of the minor cheliped, with fingers subequal to palm (much longer than palm in A. arenaria ); from A. canalis by the less projecting rostrum, the larger, stouter eyestalks, and the absence of a dense row of fusiform setae on the ventral surface of the ischium; from A. australis by the ventrally smooth chelipeds (rugose in A. australis ) and the absence of dense fringes of plumose setae on the flanks of the third to fifth abdominal somites (see Kensley & Heard 1990; Rodrigues & Shimizu 1992).

Axianassa ngochoae n. sp. is presently the only species of Axianassa known from the central-western Pacific, which is part of the vast Indo-West Pacific province. Based on two key morphological features of Axianassa , the shape of the antennal acicle (bifid — dagger-shaped, without mesial tooth — dagger-shaped, with mesial tooth) and the presence/absence of a spiniform ventral process on the first abdominal somite, A. ngochoae n. sp. appears to be closest to A. arenaria from the Gulf of Mexico. Both species have a dagger-like antennal acicle, lacking a mesial tooth, and the first abdominal somite produced into a strong spiniform process ventrally, especially in males, but differ by several important features mentioned above.