Axianassa Schmitt, 1924

Komai, Tomoyuki, 2014, A New Species of the Mud Shrimp Genus Axianassa (Crustacea: Decapoda: Gebiidea: Axianassidae) from Japan, Species Diversity 19, pp. 141-149: 141-147

publication ID 10.12782/sd.19.2.141

persistent identifier

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scientific name

Axianassa Schmitt, 1924

sp. nov.

Genus Axianassa Schmitt, 1924   Axianassa japonica   sp. nov. [New Japanese name: Nihon-suna-shako-ebi] ( Figs 1–5 View Fig View Fig View Fig View Fig View Fig )

Material examined. Holotype: male (cl 3.8 mm), Andono-hana, Shionomisaki, Kushimoto , Wakayama Prefecture, 15 m, under rock on sand bottom, 30 October 1996, SCUBA diving, coll. K. Nomura, CBM-ZC 12479.  

Description. Body ( Fig. 1 View Fig ) with sparse long, erect setae on dorsal surface; integument rather soft.

Carapace ( Figs 1 View Fig , 2A View Fig ) with straight linea thalassinica extending along entire length and well-defined cervical groove passing beyond midlength of carapace; anterolateral margin with rounded lobe just inferior to end of linea thalassinica; pterygostomial margin rounded, fringed with setae increasing in length ventrally; anterior part with short dorsolateral ridges, all beginning at base of eyestalks and slightly diverging posteriorly. Rostrum ( Fig. 2B, C View Fig ) flattened dorsoventrally, slightly broadened basally, distinctly longer than broad, reaching far beyond anterior margin of eyestalks to midlength of second segment of antennular peduncle, terminating in sharp tooth; lateral margins each with 4 denticles increasing in size distally; dorsal surface slightly channeled, with short longitudinal ridge extending from base of second lateral denticle to beyond rostral base on either side of midline.

Pleon ( Fig. 1 View Fig ) slightly depressed dorsoventrally. First pleomere with subtriangular pleuron terminating in blunt point ventrally. Second to fifth pleomeres all lacking dense lateral fringe or patch of plumose setae; all pleura marginally rounded, unarmed. Sixth pleomere with posterolateral angle not markedly produced, ventrolateral margin sinuous. Telson ( Fig. 2D View Fig ) 1.5 times longer than broad, greatest width at anterior 0.4, narrowing posteriorly; posterior margin broadly rounded, unarmed; dorsal surface at widest point with pair of small spines.

Eyestalks ( Fig. 2B, C View Fig ) reaching beyond midlength of rostrum; cornea occupying entire terminal portion of eyestalk, darkly pigmented in alcohol-preserved condition.

Antennular peduncle ( Fig. 2B, C View Fig ) with third segment subcylindrical, slender, not reaching midlength of fourth segment of antennal peduncle. Dorsal flagellum stouter and longer than ventral flagellum ( Fig. 2C View Fig ).

Antennal peduncle ( Fig. 2B, C View Fig ) with fourth segment elongate, subcylindrical, about 0.6 of carapace length, with sparse short to long setae; fifth segment about 0.2 times as long as fourth segment. Antennal acicle dagger-like with straight lateral margin and noticeably convex mesial margin, tapering distally to acute tip, about twice as long as wide, reaching to about 0.2 length of third segment of antennular peduncle. Flagellum reaching well beyond extended chelipeds.

Mandible ( Fig. 3A, B View Fig ) with apparently 2-articulated palp (first 2 articles fused); distal article with dense setae on extensor margin, most setae brown-blackish in color; molar and incisor processes partly fused; molar edge with 1 subacute tooth; incisor edge with row of acute or subacute teeth. Maxillule ( Fig. 3C View Fig ) with 2-articulated palp, distal article slightly recurved, directed proximally (angle about 90°); proximal endite broken off during dissection; distal endite with double row of spine-like setae in addition to slender setae. Maxilla ( Fig. 3D View Fig ) with moderately broad scaphognathite, latter bearing 5 long setae at tip of posterior lobe, these setae extending into branchial chamber; endopod simple, gradually tapering distally; proximal endite bilobed, distal lobe much narrower than posterior lobe; distal endite also unequally bilobed. First maxilliped ( Fig. 3E View Fig ) with broad, paddle-shaped endopod; exopod broadened distally, paddle-shaped, reaching distal margin of endopod; exopodal flagellum simple, slender, with a few apical setae; distal endite subovate; epipod small, subsemicircular, devoid of podobranch. Second maxilliped ( Fig. 3F View Fig ) with endopod slender, 4-segmented (ischium-merus fused segment longest); row of fine setae on mesial margins of coxa to ischium-merus); exopod long, with simple flagellum; epipod directed laterally, terminating in slender, acute lobe, with large podobranch consisting of numerous elongate lamellae (longest lamellae subequal in length to exopod).

Third maxilliped ( Fig. 5A View Fig ) slender, pediform. Coxa with small subdistal spine on dorsal surface. Basis very short. Ischium widened distally in dorsal view; crista dentata with row of 14 acute teeth, distalmost tooth longest ( Fig. 5B View Fig ). Merus longest, with prominent subdistal spine on ventral margin. Carpus short, not widened distally. Propodus more than twice length of carpus. Dactylus about half length of propodus, gradually tapering distally to blunt tip. Exopod absent. Epipod ( Fig. 3G View Fig ) large, distally bilobed, outer lobe broad, marginally multidenticulate, partially embracing podobranch, inner lobe slender, rod-like, with sparse setae; podobranch well developed; mastigobranch slender, rodlike (not visible in Fig. 3G View Fig ). Ventral margins of ischium to propodus with row of long setae.

Chelipeds (first pereopods) subequal in length, left stout- er than right. Major left cheliped ( Fig. 4A, B View Fig ) moderately robust. Ischium widened distally, with row of 5 small teeth on ventral margin; mesial surface with minute granules adjacent to ventral margin ( Fig. 4C View Fig ). Merus with dorsal margin inflated, unarmed; ventral margin slightly convex, with row of 4 small teeth (distalmost one, located at distal 0.4, strongest). Carpus cup-shaped, widened distally, unarmed. Chela about 0.9 times as long as carapace. Palm subrectangular, about 1.3 times as long as wide; dorsal surface rounded, slightly granular; lateral and mesial surfaces smooth, with few setae; ventral surface elevated into low, flat ridge with both lateral and mesial edges slightly tuberculate or crenulate, each edge with row of long setae extending onto fixed finger. Fixed finger terminating in slightly curved, acute tip, with row of tufts of setae on lateral surface adjacent to ventral margin; lateral surface with blunt longitudinal carina adjacent to cutting edge; occlusal margin compressed, with row of several teeth. Dactylus subequal in length to palm, terminating in curved, acute tip crossing tip of fixed finger; dorsal surface flat, flanked by distinct carinae, with 2 rows of long setae; occlusal margin compressed, with a few low, obtuse teeth.

Minor right cheliped ( Fig. 4D View Fig ) moderately stout. Ischium widened distally, with 4 minute denticles on ventral margin. Merus with dorsal margin gently convex, unarmed; ventral margin faintly convex, with minute denticle proximally and 2 small spines at about midlength. Carpus cup-shaped, widened distally, unarmed. Chela about 0.9 times as long as carapace. Palm subrectangular, slightly widened distally, about 1.7 times as long as wide, width about 0.8 that of palm of major cheliped; dorsal surface with single row of minute granules; lateral and mesial surfaces smooth, with few setae; ventral surface almost rounded, with 2 rows of minute granules. Fixed finger terminating in slightly curved, acute tip; lateral surface slightly elevated medially; occlusal margin with row of moderately spaced, small, unequal, acute or subacute teeth. Dactylus 1.2 length of palm, terminating in curved, acute tip crossing tip of fixed finger; dorsal surface carinate laterally; occlusal margin nearly smooth, without conspicuous teeth. Setation generally similar to that of major cheliped.

Second to fifth pereopods decreasing in length posteriorly.

Second pereopod ( Fig. 5C View Fig ) non-chelate, moderately robust, each segment unarmed. Articulation between ischium and merus strongly oblique. Merus with straight dorsal and gently convex ventral margins. Carpus cup-shaped. Propodus narrowing distally. Dactylus ( Fig. 5D View Fig ) about 0.8 times as long as propodus, gradually tapering distally to acute tip, with scattered setae on lateral surface and row of minute spiniform setae on ventral margin. Dorsal and ventral margins of merus to propodus with row of long setae (ventral setae generally longer than dorsal setae).

Third pereopod ( Fig. 5E View Fig ) moderately slender. Ischium, merus, and carpus unarmed, with sparse setae on margins (dorsal setae on merus very short); ventral margin of merus slightly sinuous. Propodus with distoventral cluster of stiff setae, possibly forming grooming apparatus ( Fig. 5F View Fig ). Dactylus ( Fig. 5F View Fig ) slightly shorter than propodus, strongly compressed laterally, terminating in slender unguis, bladeshaped with straight dorsal and gently convex ventral margins; dorsal margin bearing row of 6 small, movable spines increasing in length distally; ventral margin with comb-like row of minute spiniform setae extending from proximal 0.3 to distal 0.4 of length.

Fourth pereopod ( Fig. 5G View Fig ) generally similar to third pereopod. Propodus with distoventral cluster of stiff setae, but setae shorter and fewer than in third pereopod. Dactylus ( Fig. 5H View Fig ) with row of 8 small, movable spines on dorsal margin.

Fifth pereopod ( Fig. 5I View Fig ) slightly more slender than third or fourth pereopods, semichelate. Propodus somewhat widened distally, ventromesial distal margin produced into short, blunt process bearing small terminal movable spine ( Fig. 5J View Fig ). Grooming apparatus consisting of dense short setae on ventrodistal margin of propodus and longitudinal row of longer setae on mesial side of same segment. Dactylus ( Fig. 5K View Fig ) subspatulate, strongly twisted, recurved, terminating in slender, acuminate unguis; inner surface excavated; dorsal margin unarmed; ventral margin forming thin edge.

Gill/exopod/setobranch formula summarized in Table 1. Pleurobranchs absent. Arthrobranchs including 1 on first maxilliped, 2 each on second maxilliped through fourth pereopods, all well-developed, multilamellate; gills trichobranchiate, lamellae slender, rod-like. Epipods on mouthparts as described above. Epipods on first to third pereopods (cf. Fig. 3H View Fig ) similar in structure, becoming slightly smaller in size; each distal part divided into 2 unequal rod-like processes (inner process distinctly longer than outer); mastigobranchs slender, also rod-like, slightly tapering distally, subequal in length to distal outer process; podobranchs all multilamellate. Epipod on fourth pereopod ( Fig. 3I View Fig ) smaller than preceding ones, consisting of 2 slender, unequal rod-like processes; no podobranch or mastigobranch. Setobranchs absent. No exopods on pereopods.

First pleopod absent ( Fig. 1 View Fig ). Second to fifth pleopods ( Fig. 1 View Fig ) similar to each other, slender, biramous, devoid of appendices internae.

Uropod ( Fig. 2E View Fig ) with short, unarmed protopod. Exopod oval, with distinct transverse suture bearing 4 widely spaced teeth (second inner one strongest, other three minute); lateral margin with 3 tiny teeth including posterolateral tooth, and movable spinule just mesial to base of posterolateral tooth; dorsal surface with median ridge. Endopod oval, subequal in length to exopod, slightly overreaching posterior margin of telson, with short transverse suture slightly posterior to midlength, this not reaching to median ridge; lateral margin with small tooth slightly posterior to midlength; dorsal median ridge with minute tooth at about midlength.

Distribution. Known only from the type locality, Shionomisaki, Kushimoto, Wakayama Prefecture, at a depth of 15 m.

Ecology. The holotype was found under a rock on a sandy bottom. It may be assumed that A. japonica   is a bur- rower like other congeneric species ( Kensley and Heard 1990; Rodrigues and Shimizu, 1992; Anker 2010, 2011).

Remarks. The present new species is assigned to Axianassa   because it displays the following features: third segment of antennular peduncle elongate; scaphocerite not reduced, spiciform; third maxilliped without exopod; and second pereopod simple. However, Axianassa japonica   sp. nov. disagrees with the generic diagnosis given by Kensley and Heard (1990) in having a complete transverse suture on the uropodal exopod and an incomplete suture on the uropodal endopod, the latter suture originating from the base of a posterolateral tooth. A complete transverse suture on the uropodal exopod is also seen in A. heardi   (cf. Anker 2011), although the uropodal endopod is devoid of a suture in that species. The new species shares with A. heardi   one more character heretofore unique for the genus, viz., marginal denticles on the rostrum.

In spite of the possible close relationship between the present new species and A. heardi   , there are many differentiating characters between the two (cf. Anker 2011): (1) the rostrum is relatively narrower and terminates acutely in A. japonica   , not in a blunt tip as in A. heardi   ; (2) the carapace is provided anteriorly with two pairs of short longitudinal carinae in A. japonica   , whereas such ridges are absent in A. heardi   ; (3) the first pleuron is blunt ventrally in A. japonica   sp. nov., not terminating in an acute tooth as in A. heardi   ; (4) the telson is armed with a pair of small teeth on the dorsal surface in A. japonica   , but is unarmed in A. heardi   ; (5) the teeth of the crista dentata on the third maxilliped ischium increase in size distally in A. japonica   , the reverse of A. heardi   ; (6) the number of ventral teeth on the major cheliped ischium is fewer in A. japonica   than in A. heardi   (four versus about eight); (7) the lateral margin of the uropodal exopod is weakly serrate in A. japonica   , but smooth in A. heardi   ; and (8) the transverse suture on the uropodal exopod bears only three minute, unequally spaced teeth in A. japonica   , in contrast to about 12 subequally spaced denticles in A. heardi   . Both A. heardi   and A. japonica   are linked to Saintlauretiella heterocheir (Le Leouff and Intès, 1974)   , currently assigned to Laomediidae   , by the possession of a transverse suture on the uropodal exopod (Le Leouff and Intès 1974). Prior to the discovery of A. heardi   , the absence of transverse sutures on the uropodal rami was one of the diagnostic features of Axianassa   , discriminating it from other laomediid genera. Nevertheless, S. heterocheir   differs from all species of Axianassa   in the shortness of the third segment of its antennular peduncle.

Etymology. Named after the country from which the present new species was discovered.