Austinixa marianae, Ayón-Parente, 2021

Austinixa marianae View in CoL sp. nov.

( Figs. 1–3 View Figure 1 View Figure 2 View Figure 3 )

Zoobank: urn:lsid:zoobank.org:act:9024A9C9-37B0-4222-A0B2-A212679FECA1

Material examined. All from Marina R iviera

Nayarit at La Cruz de Huanacaxtle , Nayarit

(20°45’N 105°24’W). Holotype: male, CW 5.7, CL 2.2 mm ( ICML-EMU 12530 ), intertidal, fine sand, 2 September 2018, coll. R . García de Quevedo , ARH, MAP and JSB . Paratypes: 1 male CW 6.7, CL 2.4 mm and 1 ovigerous female, CW 6.8, CL 2.6 mm ( ICML-EMU 12531 ), same collection data as in the holotype. 1 male, CW 6.5, CL 2.1 mm ( LEMA-CCR 650 ), 27 May 2020, coll. MAP . 2 males CW 4.3–5.4, CL 1.7–1.9 mm and 1 ovigerous female, CW 7.1, CL 2.9 mm ( ICML-EMU 12532 ), 22 August 2020, coll. R . García de Quevedo and ARH , 2 males CW 4.4–6.0, CL 1.8–2.1 mm and 1 ovigerous female, CW 7.9, CL 2.7 mm ( ICML-EMU 12533 ), 23 August 2020, coll. R . García de Quevedo and ARH .

Size. Males, CW 4.3–6.7, CL 1.7–2.4 mm (N = 7); ovigerous females, CW 6.8–7.9, CL 2.6–2.7 mm (N = 3)

Diagnosis. Carapace transverse ridges on branchial regions nearly reaching orbit and turning towards posterior before reaching lateral margins; male carapace with dorsal patch of setae anterior to cardiac ridge; P4 propodus opposable margin bicarinate; P4 merus with bare depression on posterodistal half; P5 dactylus triangular in sectional view, margins serrated; male pleon triangular, telson rounded, longer than sixth pleonite.

Description. Carapace ( Fig. 3A–B View Figure 3 ) smooth, punctate, 2.7–2.8 times wider than long, high, cardiac crest extending from side to side across cardiac region, above posterior margin; sharp, non-tuberculate branchial ridges, not extending to orbit and turning laterally towards posterior end before reaching lateral margin. Male carapace ( Fig. 3A View Figure 3 ) with large patch of setae anterior to cardiac crest, narrower towards the central part. Female carapace ( Fig. 3B View Figure 3 ) slightly depressed in mid-back, with no setose dorsal patch. Rostrum with low anterior median depression, two lateral grooves between rostrum and orbital regions. Orbits approximately 0.6 times width of rostrum.

Antennae about 1.3 times longer than width of front, ( Fig. 3A–B, D View Figure 3 ) with 9 articles, third being the longest.

Third maxilliped ( Fig. 3C View Figure 3 ) ischiomerus fused, elongate; carpus almost as long as propodus; propodus and dactylus elongate, with long marginal setae, dactylus longer than propodus. Exopod with median protuberance on outer margin, f lagellum two-segmented ending in long setae.

Chelipeds of males and female ( Fig. 3F–I View Figure 3 ) similar in shape, but stouter in males. Chelae strong, stout, smooth but with a line of long plumose setae decreasing in size on internal surface, near and subparallel to inferior margin, extending from proximal margin of palm up to distal margin of pollex; palm dorsal margin with ridge along and continuing on dactylus exterior margin, nearly reaching tip, ventral margin nearly straight, with smooth concavity on distal third; pollex straight, about third to half as long as palm, cutting edge serrated, triangular tooth on proximal third followed by low concavity with a series of small teeth in males and a proximal tooth followed by a concavity and a plateau with tiny teeth in female gape very setose; dactylus almost as long as palm, def lexed downward, unarmed, cutting edge medially convex, serrated.

Pereopods2–5 ( Fig. 4A–E View Figure 4 ) slender, relative lengths P4> P3> P2> P5; P2 with flexor margin of merus proximally convex, dactylus longer than propodus, almost straight, short setae on tip; P3 similar to P2, dactyl curved, short setae on tip; P4 the strongest, merus with crest on extensor margin following to carpus, with dorsodistal depression of about one third length of merus, f lexor margin bicarinate, anterior carina serrated, covered with short setae, propodus bicarinate, anterior carina serrated and setose, margin of posterior carina with minute teeth,dactylus curved carinae on anterior and posterior faces, anterior wider and setose, posterior thinner and shorter, on distal half of dactylus; P5 dactylus almost straight, with deflected tip, triangular in sectional view, all margins serrated.

Male pleon ( Fig. 3E View Figure 3 ) with 6 non-fused pleonites plus telson, tapering distally, short marginal setae from third to sixth pleonite, longer on telson; pleonite 1 subtrapezoidal, pleonites 2–6 trapezoidal, second pleonite about half length of third, pleonites 3–6 similar in width, telson longer than sixth pleonite, distally rounded. Ovigerous female pleon ( Fig. 4J View Figure 4 ) wider than long, margins rounded, with 6 unfused pleonites plus telson, pleonite 1 about 0.8 pleonite 2 length, pleonites 3–5 of about same length, pleonite 6 slightly shorter than pleonite 5; telson shorter than pleonite 6, distal margin sinuous, apex slightly elevated.Male first gonopod( Fig.3G, H View Figure 3 )as illustrated. Male second gonopod ( Fig. 3L View Figure 3 ) much smaller than first, as illustrated.

Distribution. Only known from the marina at La

Cruz de Huanacaxtle, Nayarit, Mexico ( Fig. 1 View Figure 1 ).

Etymology. The species name honors Mariana Salgado, the beloved daughter of the first author, in thanks for her invaluable support with the illustration of the new species.

Remarks. Austinixa marianae sp. nov. is the third species of Austinixa recorded in the eastern Pacific coast. The new species can be separated from the other two species in this zoogeographical region ( A. felipensis and A. cuestai ) by several morphological differences: A. marianae sp. nov. has large branchial ridges that are absent in the other two species; the males of A. marianae sp. nov. and A. cuestai have a large dorsal patch of setae on carapace, anterior to the cardiac crest that is absent in A. felipensis , but the carapace of males and females of A. cuestai also have setose lateral regions, whereas in the new species these regions are bare. The P4 propodus is ventrally bicarinate in all three species, but only A. marianae sp. nov. has P4 with a posterodistal depression in carpus. The new species is more similar to A. roblesi , from Belize and the Atlantic coast of Panama, than to the rest of Austinixa species. Austinixa marianae sp. nov. shares all the diagnostic characteristics indicated for A. roblesi by Palacios Theil and Felder (2020a): “Carapace with each branchial region transversed by ridge, nearly reaching orbit, turning laterally sharply towards posterior; male carapace with dorsal patch of setae anterior to cardiac ridge; P4propodus opposable margin bicarinate; P4 merus with depression on posterior half of distal end of dorsal surface, depression not continuing into posterior surface”, but, in addition to the fact that the A. marianae sp. nov. and A. roblesi are distributed in two different zoogeographic regions ( Fig. 1 View Figure 1 ), they can be separated by several differences. Chelae of both males and females of A. marianae sp. nov. are similar but those on males are more robust than in females. On the other hand, in A. roblesi the fixed finger of chelae in males and females have a triangular median tooth on the inner margin that is absent in males of the new species. The dorsodistal depression in merus of P4 is setose in A. roblesi while in the new species it is bare. Dactyli of P4 and P5 of the two species could also be different, as Palacios Theil and Felder (2020a) indicated that, in A. roblesi , both P4 and P5 have dactyli with anterior and posterior ridges, but the authors did not mention any further details about those ridges. In A. marianae sp. nov. the anterior ridge of P4 is much wider than the posterior, surrounded by small setae and the posterior one is thinner. Besides, dactylus of P5 is triangular in sectional view and all three margins are serrated ( Fig. 3C–G View Figure 3 ). The serration of the P5 dactylus was not mentioned by Palacios Theil and Felder (2020a) but in their drawing of P5 (Fig. 8F), they illustrated a posterior ridge serrated in the proximal half. We could not examine specimens of A. roblesi and there is a possibility that the P4 and P5 dactyli of both species are similar. Perhaps the most obvious difference between A. roblesi and A. marianae sp. nov. is in the shape of the male pleon and telson. In A. roblesi the pleonites 2–6 are subrectangular, slightly decreasing in width, and the telson is semi-ellipsoidal ( Fig. 3P View Figure 3 ), similar in length to the sixth pleonite while the male pleon of A. marianae sp. nov. is tapering, the pleonites clearly decrease in width and the telson is much longer than the sixth pleonite and is distally rounded ( Fig. 3E View Figure 3 ). The female telson in the new species seems to be much wider than that in A. roblesi but this difference may be due to a difference in maturity of the organisms used for illustration. Gonopods, recognized as an important tool to differentiate species of brachyurans ( Martin and Abele, 1986; Manning and Felder, 1989), are also different in both species. The apex of the first male gonopod in A. roblesi is composed of two concave plaques, one a little longer than the other ( Fig. 3N, O View Figure 3 ), while in the new species the gonopod ends in an elongated structure on one side, longer than a distally truncated plate on the other side ( Fig. 3J, L View Figure 3 ).

In the same way as A. roblesi , the new species can be separated from the other species by the differences that Palacios Theil and Felder (2020a) found between A. roblesi and the rest of the species. That is, with the exception of A. chacei , Austinixa beherae (R.B. Manning and Felder, 1989) , and A. roblesi , A. marianae sp. nov. can be distinguished from the rest of the Austinixa species because the members of these species have branchial ridges that fall near orbits and bend backward before reaching lateral margins, however, unlike Austinixa chacei (Wass, 1955) and A. beherae , males of A. roblesi and A. marianae sp. nov. have a setal patch anterior to the cardiac crest and a depression on the posterodistal surface of merus of P4.