Axianassa linda sp. nov.

(Fig. 8–11)

Type material. Holotype: 1 male (cl 5.3 mm), MZUSP 34082, Pacific coast of Panama, Playa El Agallito, intertidal mud flat near mangroves, in burrow, coll. A. Anker, J.F. Lazarus, T. Kaji, 22.iii.2015. Paratypes: 1 male (cl 5.0 mm), 1 female (cl 8.1 mm), MZUSP 34400, same collection data as for holotype; 1 male (cl 4.5 mm), MZUSP 34401, same collection data as for holotype.

Additional material. 1 male (cl 6.3 mm), MZUSP 34402, 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 occasional erect setae; rostrum subtriangular, broadly rounded distally, reaching well beyond anterior margin of eyestalks, lateral margins not toothed, fringed with setae; linea thalassinica straight, running entire length of carapace; cervical groove deep, crescent-shaped in dorsal view; branchiostegial margin slightly elevated; pterygostomial region rounded, not protruding, fringed with setae (Fig. 8 A–C).

Pleon thinly sclerotised, smooth; dorsal surface with scattered setae of various length; lateral surface of first pleuron with curved, broad, posteroventrally directed depression, ventral margin produced into small subacute process in males, with blunt lobe in females; second to sixth pleura with ventrolateral surface bearing broadly U-shaped depression, most conspicuous on second and third pleura, ventral margin unarmed, almost straight, fringed with some stiff setae locally (Fig. 8 D). Telson broad, convex proximally, smoothly tapering posteriorly, posterior margin broadly rounded, neither lateral nor posterior margin with armature (Fig. 8 E).

Eyestalks rounded distally; cornea moderately developed compared to eyestalk, in subterminal position, moderately pigmented (Fig. 8 B). Antennular peduncle with third article elongate, subcylindrical, slender, reaching half-length of fourth article of antenna; ventral flagellum slender, about half-length of much stouter dorsal flagellum (Fig. 8 A). Antennal acicle relatively broad at base, tapering distally, short, with tip not reaching 0.2 length of fourth article of antennal peduncle, mesial margin smooth or with variously developed tooth; fourth article of antennal peduncle subcylindrical, elongate, much more robust than third article (Fig. 8 A, F, 10E, G).

Mouthparts typical for genus (cf. Kensley & Heard 1990; Rodrigues & Shimizu 1992; Anker 2011a; Komai 2014). Third maxilliped pediform; coxa with projecting sharp dorsomesial tooth; basis with minute dorsomesial spinule on distal margin; ischium about as long as merus, with well-developed crista dentata consisting of about 13 teeth, proximal-most tooth much smaller, ventral margin occasionally with thick fusiform setae; merus with several rows of thick fusiform setae on distoventral surface; carpus vase-shaped, about half as long as merus; propodus as long as merus; dactylus about half-length of propodus; ventral margin of all articles with long fine setae (Fig. 8 G–J, 10F, H, I).

First pereiopods (chelipeds) stout, somewhat unequal in size, asymmetrical in shape (Fig. 9), weaker in females (Fig. 11 C). Major cheliped robust; ischium with several widely spaced minute tubercles or denticles on ventrolateral margin, without strong teeth; 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; carpus cupshaped, ventral margin with large blunt projection; chela ovate, somewhat compressed laterally; palm about 1.8 times as long as high in males, covered with minute granules near base of pollex and dactylus, on both mesial and lateral surfaces, ventral margin rugose proximally; fingers about 0.6 length of palm, very stout, pollex slightly shorter than dactylus; cutting edge of pollex with one very stout tooth proximal to mid-length and some rugosities or very low teeth in proximal half; cutting edge of dactylus with shallow hiatus at about mid-length and several blunt teeth distal to this hiatus (Fig. 9 A–C, G). Minor cheliped slightly smaller and less robust than major cheliped; ischium and merus similar to those of major cheliped; carpus without conspicuously projecting ventral margin; chela somewhat more slender compared to major chela; palm with granules present only on mesial side; fingers slightly shorter than palm; cutting edges of pollex and dactylus with blunt, irregularly shaped teeth, most rounded or subtriangular, without large and protruding teeth (Fig. 9 D–F, H).

Second pereiopod stout; merus, carpus and propodus smooth, with numerous long thin setae along ventral margin; dactylus about half as long as propodus, with crenulated ventral margin (Fig. 10 A). Third pereiopod relatively robust; ischium, merus and carpus smooth, with few setae; propodus with distoventral brush of stiff setae; dactylus slightly shorter than propodus, dorsal margin with row of corneous spines, distoventral margin slightly expanded, with comb-like row of minute spiniform setae (Fig. 10 B). Fourth pereiopod similar to third in general configuration, more slender (Fig. 10 C). Fifth pereiopod more slender than third and fourth; propodus subchelate, ending in short blunt tooth, latter concealed by dense stiff setae; dactylus subspatulate, somewhat twisted and excavated mesially, with row of minute setae on edge subdistally (Fig. 10 D).

First pleopod absent in males; 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 or three posteriorly directed teeth, distal-most strongest (Fig. 8 K). Gill/exopod formula typical for genus (cf. Kensley & Heard 1990; Komai 2014); first maxilliped without podobranch.

Colouration. Hyaline white with pale straw-yellowish tinge; inner organs yellowish or reddish (Fig. 11).

Etymology. The new species’ name is derived from the Spanish word “ linda ”, meaning pretty or beautiful, referring to its elegant appearance; used as a noun in apposition.

Type locality. Playa El Agallito, Azuero Peninsula, Pacific coast of Panama [note: accidentally misspelled as “Playa El Aguillito” in the original descriptions of Leptalpheus azuero Anker, 2011 and L. hendrickxi Anker, 2011, in Anker (2011b)].

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

Ecology. Intertidal and shallow subtidal (less than 0.5 m) mud flats near mangroves or mangrove creeks; in burrows in mud.

Remarks. Axianassa linda sp. nov. appears to be variable in one important character commonly used in the taxonomy of the genus, which is the presence or absence of a tooth on the mesial margin of the antennal acicle (Fig. 8 F, 10E, G). The new species can be easily separated from the other three eastern Pacific species of the genus, viz. A. canalis, A. darrylfelderi and A. mineri, by the presence of thick fusiform setae on the distoventral margin of the third maxilliped merus (absent in the other three species); from A. canalis and A. darrylfelderi by the ventrally unarmed first pleuron in females (vs. with a strong ventral process in both sexes in A. canalis and A. darrylfelderi); specifically from A. canalis by the ventromesial margin of the cheliped merus finely denticulate (vs. with a stout sharp tooth in A. canalis); specifically from A. darrylfelderi by the significantly shorter antennal acicle, not reaching 0.2 length of the fourth article of the antennal peduncle (vs. reaching 0.3 length of this article in A. darrylfelderi); the ventrolateral margin of the cheliped ischium finely denticulate (vs. armed with several strong sharp teeth in A. darrylfelderi); and the pale-yellowish colour (vs. reddish pink in A. darrylfelderi); and specifically from A. mineri by the dagger-shaped antennal acicle (vs. distally bidentate in A. mineri); 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 the third maxilliped merus and carpus unarmed ventrally (vs. armed with sharp teeth on ventral margin in A. mineri) (cf. Kensley & Heard 1990; Anker & Lazarus 2015; see also Figs. 1–5, 7).

Axianassa linda sp. nov. also differs from its four western Atlantic congeners, viz. A. jamaicensis, A. australis, A. arenaria Kensley & Heard, 1990, and A. intermedia Schmitt, 1924 . For instance, the new species can be separated from A. jamaicensis, A. australis and A. arenaria by the presence of thick fusiform setae on the distoventral margin of the third maxilliped merus and sometimes ischium (absent in the other three species); from A. australis and A. arenaria by the first pleuron ventrally unarmed in females (vs. armed with a strong ventral process in both sexes in A. australis and A. arenaria); from A. jamaicensis, A. australis and A. arenaria by the ventrolateral margin of the cheliped ischium finely denticulate, without strong teeth (vs. armed with strong teeth in the other three species); from A. jamaicensis, A. arenaria and A. intermedia Schmitt, 1924 by the ventrolateral margin of the cheliped merus finely denticulate (vs. denticulate and additionally with a small top medium-sized tooth in A. jamaicensis and A. arenaria or with rough distal serrations in A. intermedia); from A. jamaicensis and A. australis by the pale-yellowish colour (vs. reddish pink in A. jamaicensis and A. australis); specifically from A. arenaria by the ventrally unarmed second to fifth pleura (vs. each armed with a small tooth in A. arenaria) and the lateral margins of the telson without a small notch proximally (with such a notch in A. arenaria); and specifically from A. intermedia, to which it has most resemblance, by the crista dentata of the third maxilliped bearing several conspicuously larger teeth among smaller teeth (vs. bearing all small, and also more numerous, teeth in A. intermedia); and the comparatively longer major cheliped fingers in males, being at least 0.6 times as long as palm (vs. less than 0.5 times in A. intermedia) (cf. Kensley & Heard 1990; Rodrigues & Shimizu 1992; see also Fig. 6).

The new species can be separated from the four western Pacific species of Axianassa, most easily from A. heardi Anker, 2011 and A. japonica Komai, 2014, by the uropodal exopod lacking a toothed diaeresis (vs. with a toothed diaeresis in A. heardi and A. japonica) and the lateral margins of the rostrum without teeth (vs. conspicuously dentate in A. heardi and A. japonica). It differs from A. sinica Liu & Liu, 2010 and A. ngochoae Anker, 2010 by the shorter antennal acicle, not reaching 0.2 length of the fourth article of the antennal peduncle (vs. reaching or overreaching 0.25 length of this article in A. ngochoae and A. sinica), and the major cheliped carpus bearing a blunt ventral projection (absent in the other two species); and specifically from A. sinica by the broadly rounded rostrum (vs. distinctly pointed in A. sinica) (cf. Anker 2010, 2011a; Liu & Liu 2010; Komai 2014).

It is interesting to note that the peculiar fusiform (or villiform) setae are present on the third maxillipeds of A. linda sp. nov., A. intermedia and A. canalis . However, they are present on different articles of the third maxilliped, i.e. on the merus and sometimes also on the ischium in A. linda sp. nov. (Fig. 8 G, H, 10F, H, I), on the merus only in A. intermedia (de Man 1928: fig. 2a–c; Kensley & Heard 1990: fig. 2J), and on the ischium only in A. canalis (Fig. 3 B; see also Kensley & Heard 1990: fig. 7D). A similar dense field of thickened setae was also observed in the snapping shrimp Alpheus villus Kim & Abele, 1988, where it is found on the penultimate (= carpal) article of the third maxilliped (Kim & Abele 1988: fig. 34d). Their function in these four taxa remains enigmatic.