Axianassa christyi, Anker, Arthur & Pachelle, Paulo P. G., 2016

Anker, Arthur & Pachelle, Paulo P. G., 2016, Mud-shrimps of the genus Axianassa Schmitt, 1924 from Panama, with description of two new species (Decapoda: Gebiidea: Laomediidae), Zootaxa 4111 (2), pp. 101-125: 117-121

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Axianassa christyi

sp. nov.

Axianassa christyi   sp. nov.

( Fig. 12–14 View FIGURE 12 View FIGURE 13 View FIGURE 14 )

Type material. Holotype: 1 female (cl 12.6 mm), MZUSP 34093, Pacific coast of Panama, Las Perlas Archipelago, Isla Casayeta, small bay with mud flat fringed by rocks and mangroves, 0.3 m, in burrow, coll. A. Anker, 20.iv. 2015.

Description. Carapace smooth, with some scattered erect setae, more numerous on dorsal surface near posterior margin; rostrum triangular, pointed distally, not reaching beyond anterior margin of eyestalks, lateral margins entire, fringed with setae; linea thalassinica almost straight, running entire length of carapace; cervical groove deep, crescent-shaped in dorsal view; pterygostomial region rounded, not protruding, fringed with setae ( Fig. 12 View FIGURE 12 A –C).

Pleon thinly sclerotised, smooth; dorsal surface with scattered erect setae of various length; lateral surface of first pleuron smooth, ventral margin blunt in female, condition in males currently unknown; second to sixth pleura with ventrolateral surface smooth, ventral margin of each pleuron more or less rounded, furnished with dense rows of setae ( Fig. 12 View FIGURE 12 D, 14 B). Telson broad, convex proximally, smoothly tapering posteriorly, posterior margin broadly rounded, neither lateral nor posterior margin with armature ( Fig. 12 View FIGURE 12 E).

Eyestalks triangular, tapering distally; cornea small compared to eyestalk, in terminal position, poorly pigmented ( Fig. 12 View FIGURE 12 A, B). Antennular peduncle with third article elongate, subcylindrical, slender, reaching halflength of fourth article of antenna; ventral flagellum slender, less than half-length of much stouter dorsal flagellum ( Fig. 12 View FIGURE 12 A). Antennal acicle dagger-like, relatively narrow at base, tapering distally, with tip (broken on both sides in holotype) reaching at least 0.25 length of fourth article of antennal peduncle, mesial margin straight, without tooth; fourth article of antennal peduncle subcylindrical, elongate, much more robust than third article ( Fig. 12 View FIGURE 12 A, F).

Mouthparts typical for genus. Third maxilliped pediform; coxa with small sharp mesiodorsal tooth; basis with minute dorsomesial spinule on distal margin; ischium slightly shorter than merus, with well-developed crista dentata composed of 14 teeth, proximal four teeth being much smaller; merus without specific features; carpus vase-shaped, about half as long as merus; propodus as long as merus; dactylus about 0.6 length of propodus; ventral margin of all articles with long fine setae ( Fig. 12 View FIGURE 12 G –J).

First pereiopods (chelipeds) moderately stout, slightly unequal in size, asymmetrical in shape ( Fig. 13 View FIGURE 13 A, C); male chelipeds currently unknown (probably similar but stouter and larger). Major cheliped fairly robust; ischium with three widely spaced sharp teeth on ventrolateral margin; merus inflated, with strongly convex dorsal margin and slightly convex ventromesial and ventrolateral margins; ventromesial margin with row of widely spaced small tubercles or denticles, one of them developed into much more conspicuous, projecting, medium-sized tooth; carpus cup-shaped, with unarmed ventral margin; chela ovate, compressed laterally; palm 1.9 times as long as high in female, smooth on mesial and lateral surfaces, ventral margin smooth proximally; fingers almost as long as palm, moderately stout, pollex slightly shorter than dactylus; cutting edge of pollex with several blunt teeth in proximal half, distal-most stoutest, numerous smaller rounded teeth in distal half, two of them conspicuously larger, especially more proximal tooth fitting into hiatus on opposed cutting margin of dactylus; cutting edge of dactylus with few very low blunt teeth in proximal half, one much larger rounded tooth at about mid-length, followed by short hiatus, and numerous small rounded teeth in distal half ( Fig. 13 View FIGURE 13 A, B).

Minor cheliped slightly smaller and distinctly more slender than major cheliped; ischium, merus and carpus generally similar to those of major cheliped, ischium with two teeth on ventrolateral margin; chela more slender compared to major chela; fingers noticeably longer than palm; cutting edge of pollex with small rounded teeth and three much larger triangular sharp teeth at about 0.3, 0.6 and 0.8 length, respectively; cutting edge of dactylus serrated with small blunt teeth, with one tooth at about mid-length being somewhat larger than others ( Fig. 13 View FIGURE 13 C, D).

Second pereiopod stout; merus, carpus and propodus smooth, with numerous long thin setae along ventral margin; dactylus about half as long as propodus, with feebly crenulated ventral margin ( Fig. 13 View FIGURE 13 E). Third pereiopod moderately robust; ischium, merus and carpus smooth, moderately setose; propodus with distoventral brush of stiff setae; dactylus subequal to propodus, dorsal margin with row of corneous spines, distoventral margin slightly expanded, with comb-like row of minute spiniform setae ( Fig. 13 View FIGURE 13 F). Fourth pereiopod similar to third in general configuration, slightly more slender ( Fig. 13 View FIGURE 13 G). Fifth pereiopod more slender than third and fourth; propodus subchelate, ending in short blunt tooth, latter partly concealed by dense stiff setae; dactylus subspatulate, somewhat twisted and depressed mesially, with row of minute setae on edge subdistally ( Fig. 13 View FIGURE 13 H).

First pleopod in females consisting of short base and longer distal article, latter fringed with setae along margins. Second to fifth pleopods similar, biramous; protopods unarmed. Uropod with broadly ovoid exopod and endopod, both unarmed dorsally; exopod without diaeresis, distolateral margin with two small posteriorly directed teeth situated at some distance from each other, distal tooth stronger than proximal one; distal margins of exopod and uropod with slender spiniform setae ( Fig. 12 View FIGURE 12 K, L). Gill/exopod formula typical for genus (cf. Kensley & Heard 1990; Komai 2014); first maxilliped without podobranch.

Colouration. Pale yellowish with reddish-pinkish frontal region of carapace, antennular and antennal peduncles, and chelipeds; inner organs visible by translucence bright orange ( Fig. 14 View FIGURE 14 ).

Etymology. The new species is named after our colleague, Dr. John Christy (Smithsonian Tropical Research Institute) for his important contributions on ecology and behaviour of Decapoda   .

Type locality. Isla Casayeta, Las Perlas Archipelago, Pacific coast of Panama.

Distribution. Eastern Pacific: presently known only from Panama (Las Perlas Archipelago).

Ecology. Shallow subtidal (less than 0.5 m) mud flats near mangroves; in burrows.

Remarks. Axianassa christyi   sp. nov. is morphologically closest to the western Atlantic A. arenaria   , the western Pacific A. ngochoae   and A. sinica   , and the eastern Pacific A. linda   sp. nov., based on the shape of the antennal acicle (variable in the latter species), the absence of a diaeresis on the uropods, the non-dentate rostrum, as well as several other morphological features (cf. Figs. 8–11 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 11 ; Kensley & Heard 1990; Anker 2010, 2011a; Liu & Liu 2010; Komai 2014). The new species differs from A. arenaria   by the ventrally unarmed second to fifth pleura (vs. each armed with a small tooth in A. arenaria   ) and a more triangularly projecting rostrum (vs. being more rounded, with a small apical point, in A. arenaria   ); from both A. ngochoae   and A. linda   sp. nov. by the more projecting, distally subacute rostrum (vs. being broadly rounded in A. ngochoae   and A. linda   sp. nov.); from A. ngochoae   , A. sinica   , and A. linda   sp. nov. by the presence of a small tooth at about mid-length of the ventromesial margin of the cheliped merus (vs. finely denticulate, without conspicuous teeth in A. ngochoae   and A. linda   sp. nov. or with a much larger, more distally positioned tooth in A. sinica   ); from both A. ngochoae   and A. linda   sp. nov. by the pale reddish-pink colour pattern (vs. whitish or pale-yellowish, without reddish chromatophores in A. ngochoae   and A. linda   sp. nov.); from A. sinica   by the rostrum not reaching the end of the eyestalks (vs. by far overreaching the eyestalks in A. sinica   ); and specifically from A. linda   sp. nov. by the much longer antennal acicle, reaching to about 0.3 length of the fourth article of the antennal peduncle (vs. not reaching 0.2 length in A. linda   sp. nov.), the major cheliped carpus with a smooth ventral margin (vs. with a conspicuous blunt ventral projection in A. linda   sp. nov.), the pollex of the minor cheliped chela armed with three sharp teeth on the cutting edges, in addition to numerous smaller teeth (vs. armed only with small teeth in A. linda   sp. nov.); and the third maxilliped merus and ischium without thick fusiform setae (always present on the merus and sometimes also on the ischium in A. linda   sp. nov.).

Axianassa christyi   sp. nov. can be distinguished from the remaining eastern Pacific species of Axianassa   , for instance from A. mineri   , A. canalis   and A. darrylfelderi   by the dagger-shaped, mesially unarmed antennal acicle (vs. distally bifurcating in A. mineri   or armed with a mesial tooth in A. canalis   and A. darrylfelderi   ); from A. canalis   and A. darrylfelderi   by the ventrally unarmed first pleuron, at least in females (vs. armed with a subacute projection in both sexes in A. canalis   and A. darrylfelderi   ); from A. mineri   and A. canalis   also by the pale yellowreddish colouration (vs. whitish or pale-yellowish in A. mineri   and A. canalis   ); specifically from A. mineri   by the presence of a single row of corneous spinules on the dactyli of the third and fourth pereiopods (vs. with several rows in A. mineri   ); and specifically from A. canalis   by the absence of thick fusiform setae on the third maxilliped ischium (vs. with thick fusiform setae in A. canalis   ) and the ventral margin of the cheliped merus with a small, barely projecting tooth (vs. with a very strong tooth in A. canalis   ) (cf. Kensley & Heard 1990; Anker & Lazarus 2015; see also Figs. 1 –5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 7 View FIGURE 7 ).

Axianassa christyi   sp. nov. can be also separated from the remaining western Atlantic species of the genus, viz. A. jamaicensis   , A. australis   and A. intermedia   , by the distally pointed, triangular rostrum (vs. distally rounded in the other three species) and the mesially unarmed antennal acicle (vs. armed with a tooth in the other three species); specifically from A. jamaicensis   by the major cheliped carpus ventrally smooth (vs. with bumps or blunt teeth in A. jamaicensis   ); specifically from A. australis   by the first pleuron unarmed ventrally (vs. with a sharp process in A. australis   ); and specifically from A. intermedia   by the absence of thick fusiform setae on the third maxilliped merus (vs. with fusiform setae in A. intermedia   ) (cf. Kensley & Heard 1990; Rodrigues & Shimizu 1992). The new species is easily distinguishable from the western Pacific A. heardi   and A. japonica   , using the same morphological criteria as for A. linda   sp. nov. (see above and Anker 2011 a; Komai 2014).


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