Ambidexter cochensis, Rodríguez & Lira, 2022

Rodríguez, Pedro & Lira, Carlos, 2022, A new species of shrimp, genus Ambidexter Manning & Chace, 1971 (Decapoda Processidae), from southeastern Caribbean Sea, Venezuela, with key to genus, Zootaxa 5219 (3), pp. 287-294 : 288-293

Ambidexter cochensis sp. nov.

( Figs. 1–2 )

Ambidexter sp. Rodríguez et al. 2020: 195, fig. 10a–f.

Ambidexter symmetricus Márquez, 1988: 48 , fig. 37 (?); Vera-Caripe & Lira 2019: 21, plates 15A–C (?).

Type material. Venezuela: holotype: male (cl 3.2 mm), MBUCV-XI-5559, El Amparo beach, Coche Island, shallow bed of the seagrass T. testudinum , 10 m from the coast (10°44’9.17’’N 63°55’1.90’’W), depth: 0, 60 m, nocturnal net sample, col. P. Rodríguez, D. Morales, 08.10.2018 ; paratype: ovig. female (cl 5.5 mm), MBUCVXI-5560, same collecting data as the holotype .

Additional material: Venezuela: 2 males (cl 2.7–3.95 mm), GIC-938, El Amparo beach, Coche Island, shallow seagrass bed of T. testudinum , 70 m from the coast (10°44’7.37’’N 63°55’1.68’’W), depth: 0.50 m, nocturnal net sample, col. P. Rodríguez, J. Rojas, 23.06.2018 ; 13 males (cl 2.4–5.2 mm), 1 female (cl 4.9 mm), 5 ovig. females, (cl 5.7–6.8 mm), MBUCV-XI-5561, same collecting data as the type material ; 1 male (cl 3.2 mm), 2 ovig. female, (cl 4.6–5.9 mm), GIC-914, in Polychaeta reef, 2009, without any more data; 1 male (cl 2.6 mm), GIC-606, El Manglillo, Margarita Island , without any more data .

Description. Rostrum short, not overreaching anterior margin of eye ( Fig. 1A, B ), slightly deflexed, unarmed, apex bifid, lower tooth longer than the upper tooth; there are a few simple setae inserted in the bifurcation between both teeth. Distal portion of the ventral margin of rostrum almost straight, proximal portion slightly convex and with small setae ( Fig 1C ). Antennal spine present. Anterolateral margin of carapace rounded. Carapace smooth, without granules and no other spines are present. Eyes large, cornea well pigmented. Ventral margins of abdominal pleurae fringed with fine setae (not in drawing). Fifth abdominal somite with a small subacute projection on the posterolateral margin, sixth abdominal somite 1.3 times as long as fifth, posterolateral margin projected in a strong spine ( Fig. 1D ). Telson 1.7 times as long as sixth somite and 2.6–2.7 times as long as wide, with two pair of dorsal spines; transverse row of setae placed between anterior margin and anterior pair of dorsal spines and three longitudinal rows of setae, one central and one on each side, at the level of the dorsal spines, extending from the posterior margin of the transverse row of setae to nearly the posterior margin of telson; distance between the anterior margin of telson and anterior pair of dorsal spines about 0.3–0.4 times the distance between both pair of dorsal spines ( Fig. 1E ). Apex of telson produced into a sharp median point; two pair of distal spines, mesial pair stronger than either the lateral pair or the median point. There are a pair of long plumose setae and two pairs of small simple setae adjacent to the median point ( Fig. 1F ).

Antennular peduncle extends beyond the rostrum by slightly more than half of the basal article. Basal article over three times as long as the penultimate which is subequal or slightly shorter than the ultimate article and armed with a small ventral spine set about midlength. Stylocerite slightly broad; distal margin subtruncate, nearly straight; lateral margin armed with a small spinule, and with a line of setae posterior to spinule ( Fig. 1G ). Inner flagellum near twice the carapace length, outer flagellum slightly over half the carapace length. Thickened setigerous portion consists of 13–16 articles and the slender portion consists of 5–9 articles.

Scaphocerite about 5–6 times as long as wide, extends to the distal margin of the ultimate article of the antennular peduncle; anterior margin blunt angled; anterolateral spine not overreaching the blade ( Fig. 1H ). Antennal peduncle slightly overreaching the distal margin of penultimate article of antennular peduncle. Antennal flagellum slightly longer than the body.

Mouthparts not dissected, appearing typical for the genus in external view. Third maxilliped ( Fig. 1I ) overreaching scaphocerite by the length of the ultimate article and extending beyond the antennular peduncle by the length of the ultimate article and the distal half of penultimate. Antepenultimate article slightly longer than the combined length of the penultimate and ultimate articles. Penultimate article subequal to ultimate; mesially armed with two strong narrow spines on the distal margin. Ultimate article with distal half compressed, armed with short and strong spines along both margins, those of the inner margin a little larger than those of the outer margin, and with seven long strong movable spines placed four on the compressed half and three on the proximal half of the article ( Fig. 1J ). Exopod well developed.

First pair of pereiopod symmetrical both chelate; palm 1.5–1.6 times as long as fingers; chela about 2.5 times as long as the carpus; merus subequal or slightly shorter than the chela and carpus combined ( Fig. 2A ). Second pair of pereiopod symmetrical, both chelate; palm 1.3–1.4 times as long as fingers; carpus four times as long as chela; merus 2.3–2.6 times as long as chela; ischium subequal to merus. Carpus subdivided into 9 to 11 articles. Merus divided into four articles (quite difficult to see on some specimens after preservation) ( Fig. 2B ).

Third pereiopod slender; propodus 3–4 times as long as dactylus; carpus 1.5–1.7 times as long as propodus; merus 1.5 times as long as propodus and subequal to carpus, armed with 4 or 5 movable spines on the outer surface; ischium 0.8 times as long as propodus and 0.5 times as long as merus, armed with two movable spines on the outer surface. Combined lengths of propodus and carpus subequal or slightly longer than combined lengths of merus and ischium ( Fig. 2C ). Fourth pereiopod slender, longer than the third and fifth; propodus three times as long as dactylus; carpus 1.5 times as long as propodus; merus 1.2–1.4 times as long as propodus and subequal or slightly longer than carpus, armed with 3 or 4 movable spines on the outer surface; ischium 0.5 times as long as merus, armed with two movable spines on the outer surface. Combined lengths of propodus and carpus slightly longer than combined lengths of merus and ischium ( Fig. 2D ). Fifth pereiopod slender; propodus 3 to 4.4 times as long as dactylus; carpus 0.7 times as long as propodus; merus 1.15 times as long as carpus; ischium 0.5 times as long as merus. Combined lengths of propodus and carpus subequal to combined lengths of merus and ischium; merus and ischium unarmed ( Fig. 2E ).

Endopod of female first pleopod less than half as long as the exopod ( Fig. 2F ). Endopod of male first pleopod ( Fig. 2G ) with tip rounded, about half as long as the exopod. Appendix interna indistinctly fused to the endopod. Second pleopod of male with appendix masculina, more than twice as long as the appendix interna ( Fig. 2H ), and armed with four apical setae; other setae similar in size to the apicals is located posterior to these and a small seta is set at about three fourths of the tip ( Fig. 2I ).

Uropods overreaching the posterior margin of telson. Uropodal exopod with lateral margin straight, ending in a strong tooth, with a strong movable spine, adjacent to the tooth; diaeresis extends across the exopod. Uropodal endopod elongated with the lateral margin rounded, upper surface sparsely setose ( Fig 1E ).

Color in life. Body semitransparent, with small red-orange chromatophores. Ovigerous mass pale orange.

Type locality. El Amparo beach, Coche Island , Venezuela.

Distribution. Presently known with certainty only from Coche and Margarita Islands, Venezuela.

Etymology. This new species is named after the type locality, Coche Island, Venezuela.

Ecology. All the specimens from the type locality were collected only in seagrass beds of T. testudinum , depth less than 1m. The field notes of some specimens deposited at the GICUDONE seems to indicate that they inhabit Polychaeta reefs too.

Remarks. Ambidexter cochensis sp. nov. can be distinguished from all other species of the genus by a combination of morphological characters (see Table 1 and below).

This new species is morphologically closer to A. swifti from the eastern Pacific, with which it shares the stylocerite armed with a spinule on the lateral margin, rostrum with apex bifid and the relative length of the scaphocerite (5–6 times as long as wide). However, they can be separated from each other by the number of carpal articles of the second pereiopods (9–11 in A. cochensis sp. nov. versus 12–13 in A. swifti ), another difference between these species is the number of articles of both the thickened and the slender portion of the outer antennular flagellum (13–16 articles on the thickened portion and 5–8 on the slender portion in A. cochensis sp. nov. versus 12–13 articles on the thickened portion and 9–10 on the slender portion in A. swifti ). The other eastern Pacific species, A. panamensis , also possess the stylocerite armed with a spinule on the lateral margin, however it may be easily distinguished from this new species by the rostrum with a simple apex ( Abele 1972).

This new species may be differentiated from the amphi-american species A. symmetricus by having the stylocerite armed with a spinule on the lateral margin while the stylocerite is rounded and laterally unarmed in A. symmetricus ( Manning & Chace 1971; Santana-Moreno et al. 2016; Moraes et al. 2018), and by the relative length of the scaphocerite (5–6 times as long as wide in A. cochensis sp. nov. versus 4.3 times as long as wide in A. symmetricus ) ( Manning & Chace 1971).

Another difference between these four species is the setation pattern on the telson (transverse row of setae between the anterior pair of spines and three longitudinal row of setae, one central and one lined across both pair of dorsal spines in A. cochensis sp. nov. versus only the transverse row of setae between the anterior pair of spines in all other species of the genus) ( Manning & Chace 1971; Abele 1972). This setation pattern on the telson has been used as a taxonomic character that allow one to distinguish the processid shrimp Processa manningi De Grave & Felder, 2012 from related species like P. famelica Manning & Hart, 1991 and P. vossi Manning, 1992 ; and from less related species like P. guyanae Holthuis, 1959 , P. hemphilli Manning & Chace, 1971 and P. vicina Manning & Chace, 1971 ( De Grave & Felder 2012; Santana-Moreno et al. 2013). A final difference is the number and disposition of setae on the appendix masculina of the male second pleopod. There are only four apical strong setae in A. symmetricus and A. swifti ( Manning & Chace 1971; Abele 1972; Rasch & Bauer 2016a). Besides these four apical setae, there are four proximal weaker lateral setae subequally spaced from the distal tip of the appendix interna in A. panamensis ( Abele 1972) . In A. cochensis sp. nov., there are only two, one similar in size to the apicals is located posterior to these and a small setae is set at about three fourths of the tip.

Only A. symmetricus had been reported from insular and eastern regions in Venezuela ( Rodríguez 1980; Márquez 1988; Vera-Caripe & Lira 2019). This species was found at the El Saco Lagoon, Coche Island (less than 5 km away from the type locality of A. cochensis sp. nov.) by Vera-Caripe & Lira (2019), on the basis of a single specimen collected from burrows of Upogebia omissa Gomes Corrêa. However , in the diagnosis made by the authors, there was no mention of the stylocerite structure. Because there is some overlapping with the rest of morphological features of A. cochensis sp. nov., it may be possibly that the previous record of A. symmetricus from Coche Island actually correspond with this new species.

Hernández-Ávila et al. (2007), reported from Cubagua Island, Venezuela, some specimens identified as Ambidexter sp. ; however, they did not explain why they could not identify the sample past species. A re-examination of those specimens may help to determinate whatever they belong to this new species, to other known species or to another species not described yet.

Figures

FIGURE 1. Ambidexter cochensis sp. nov., holotype, male (cl 3.2 mm), from El Amparo beach,Coche Island, Venezuela (MBUCV-XI-5559): A, frontal region of carapace, dorsal view; B, frontal region of carapace, lateral view; C, apex of the rostrum; D, abdomen in lateral view; E, telson and uropod in dorsal view; F, detail of the distal portions of telson; G, antennular peduncle; H, scaphocerite; I, third maxilliped; J, ultimate article of third maxilliped. Scale bars: A, B, D = 2 mm, C, E, G–J = 1 mm, F = 0.5 mm.

FIGURE 2. Ambidexter cochensis sp. nov., holotype, male (cl 3.2 mm), from El Amparo beach, Coche Island, Venezuela (MBUCV-XI-5559): A, first pereiopod; B, second pereiopod; C, third pereiopod; D, fourth pereiopod; E, fifth pereiopod; F, female (paratype MBUCV-XI-5560) First pleopod; G, male first pleopod; H, male second pleopod with appendix masculina and appendix interna; I, tip of appendix masculina. Scale bars: A–H = 1 mm, I = 0.1 mm.