Euryrhynchus pemoni Pereira, 1985

Pachelle, Paulo P. G. & Tavares, Marcos, 2018, The freshwater shrimp family Euryrhynchidae Holthuis, 1950 (Crustacea: Decapoda: Caridea) revisited, with a taxonomic revision of the genus Euryrhynchus Miers, 1878, Zootaxa 4380 (1) : 48-55

publication ID	https://doi.org/ 10.11646/zootaxa.4380.1.1
publication LSID	lsid:zoobank.org:pub:9DC29ECD-8C44-4F42-BA0E-9B0C830A7C73
DOI	https://doi.org/10.5281/zenodo.5694249
persistent identifier	https://treatment.plazi.org/id/03D987F9-FF95-8577-A4D4-F7E263C6B96B
treatment provided by	Plazi
scientific name	Euryrhynchus pemoni Pereira, 1985
status

Treatment

Euryrhynchus pemoni Pereira, 1985 View in CoL

( Figs. 31–37 View FIGURE 31 View FIGURE 32 View FIGURE 33 View FIGURE 34 View FIGURE 35 View FIGURE 36 View FIGURE 37 , 64A View FIGURE 64 )

Euryrhynchus pemoni Pereira, 1985: 619 View in CoL , fig. 5.

Euryrhynchus pemoni View in CoL — Magalhães 1988: 51; Pereira & García 1995: 128 (tab. 1); Pereira 1997: 3, tab. 6, figs. 1, 9d; De Grave 2007: 194; Magalhães & Pereira 2007: 114, tabs. 1–3; De Grave & Fransen 2011: 309.

Material examined. Paratypes: 1 ♂ (cl 3.2 mm), 2♀ (cl 5.3, 4.7 mm), USNM 216242 About USNM , Venezuela, between San Rafael and Salto Kamá, creek in La Gran Sabana road, coll. G. Pereira & A. Paolillo, 27.iii.1983. GoogleMaps Additional material: 1♂ (cl 5.8 mm), OUMNH.ZC.2013-05-0047, French Guiana, Cayenne , 15 Km south of Kourou , Montagne des Singes , 05.0718°N 52.6928°W, coll. O. Helke, 2012 GoogleMaps ; 1♂ (cl. 5.0 mm), MZUSP 33666 View Materials , Guyana, Potaro-Siparuni, tributary of Kuribrong River , 05°23'48''N 59°32'00''W, coll. F.C.T. Lima et al., 21.iv.2010. GoogleMaps

Type locality. Creek in La Gran Sabana road, between San Rafael and Salto Kamá ( Venezuela).

Distribution. Venezuela (La Gran Sabana), Guyana (Potaro-Siparuni) and French Guiana (Cayenne) ( Pereira 1985; present study) ( Fig. 64A View FIGURE 64 ).

Redescription. Carapace smooth, non-setose. Branchiostegite smooth, non-granulated, anterior margin produced beyond infra-orbital angle, branchiostegal groove weakly marked. Pterygostomial region angular or produced anteriorly into blunt, broad tooth. Antennal spine conspicuous, placed at same level than infra-orbital angle, partially obscuring infra-orbital angle. Hepatic and branchiostegal spines absent. Rostrum triangular in dorsal view, depressed dorsally, almost reaching or slightly overreaching distal margin of eyes, with row of few long simple setae along each dorsolateral margin ( Figs. 31A–C View FIGURE 31 , 32 View FIGURE 32 ).

Fourth thoracic sternite with transversal ridge produced into acute lobe medially. Fifth thoracic sternite with transversal ridge produced into broadly acute lobe medially. Sixth and seventh thoracic sternites with transversal ridge incomplete, interrupted medially. Eigth thoracic sternite with transverse ridge complete, median region produced anteriorly, V-shaped ( Fig. 31D, E View FIGURE 31 ).

Pleon smooth, non-setose. First to fifth pleurae with postero-ventral margin rounded. Second pleura expanded in both sexes, overlapping both first and third pleurae by almost half width. Third to fifth pleurae with long simple setae on antero-ventral margin. Sixth pleura with postero-ventral margin angular, ventromesial margin with fringe of plumose setae. First to third sternites of males and immature females with median process, third one smallest, sometimes inconspicuous. Fourth to sixth sternites smooth, unarmed. Pre-anal plate smooth, lacking longitudinal carina, distally straight.

Telson broad, up to twice as long as wide. Lateral margins of telson nearly straight, parallel, not noticeably tapering towards distolateral angle. Distal region of telson broadly rounded, fringed with numerous long, annulate, plumose setae. Distolateral margins of telson with row of few simple setae of variable length. Distolateral angle of telson with pair of cuspidate setae, mesial seta about twice as long as lateral seta. Dorsal surface of telson with two pairs of cuspidate setae, anterior pair placed on proximal third of telson length, posterior pair placed on medial third of telson length, inserted more mesially than anterior pair. Lateral margin of telson with few long, simple setae. Anal tubercles absent.

Eyes short, not overreaching proximal half of basal article of antennular peduncle. Cornea somewhat kidneyshaped in dorsal view, occupying most of distal region and lateral regions of ocular peduncle, basal line weakly marked, ommatidia hexagonal, ocellar spot (“ocellus”) absent. Ocular peduncles nearly immobile, basal articulation reduced, inconspicuous ( Figs. 31A–C View FIGURE 31 , 32A–C, E, F View FIGURE 32 ).

Antennular peduncle with stylocerite blunt, not produced distally, with cluster of long, simple setae on distodorsal region. Basal article with distolateral angle produced into sharp tooth, reaching or slightly overreaching distolateral projection of medial article, mesial margin fringed with plumose setae, proximal third with ventromesial sharp spine. Medial article almost as long as wide, fringed with plumose setae on both mesial and lateral margins, distolateral and distomesial angles bluntly produced. Distal article quadrate. Lower antennular flagellum long and uniramous. Upper antennular flagellum divided into two rami fused at base by one article; main ramus similar to lower antennular flagellum; accessory ramus shorter and thicker than other antennular flagella, consisting of 3 to 4 free articles, increasing in number in large specimens, length of articles variable, aesthetascs restricted to distal margin of apical article ( Figs. 31A, C, G View FIGURE 31 , 32A, C View FIGURE 32 ).

Antenna with scaphocerite broad, about 1.5 as long as wide, slightly overreaching antennular peduncle, lamella fringed with plumose setae, lateral margin straight or slightly convex, with sharp distal tooth slightly overreaching lamella. Carpocerite about 3 times as long as wide, reaching distal third of scaphocerite. Basicerite with sharp distolateral tooth reaching proximal fourth of carpocerite, ventral margin of basicerite produced anteriorly into broad, triangular tooth ( Figs. 31A, C View FIGURE 31 , 32A, C View FIGURE 32 ).

Mouthparts typical for genus. Third maxilliped pediform. Coxa with broad lateral plate, single arthrobranch present. Basis short, about 1/3 length of antepenultimate article of endopod. Endopod with 3 articles, furnished laterally with long simple setae; antepenultimate article longest, furnished mesially with simple setae; penultimate article about 0.7 times length of antepenultimate article, furnished mesially with rows of serrate setae; ultimate article shortest, about 0.8 times length of penultimate article, furnished mesially with rows of serrate setae. Exopod long, reaching proximal third of penultimate article of endopod, fringed with long plumose setae ( Fig. 31H View FIGURE 31 ).

First pereopod slender, short, carpus and chela overreaching scaphocerite when fully extended. Merus about twice as long as ischium. Carpus slightly longer than merus. Chela about 0.7 times length of carpus, distal half furnished ventrally with tufts of long serrulate setae, fingers equal in length with palm, fingertips corneous ( Fig. 31I View FIGURE 31 ).

Second pereopod stout, long, pair similar in form, equal or subequal in size. Surface of ischium to propodus finely granulated. Merus fused with ischium, distoventral angles with single subdistal spine, placed on mesial angle. Carpus stout in dorsal view, approximately twice as long as wide, reaching distal third of palm, distomesial angle unarmed, smooth or produced into blunt process. Chela with proximal transverse constriction near articulation with carpus, fingers with pair of blunt teeth on proximal half of each cutting edge, fingertips corneous ( Figs. 33 View FIGURE 33 , 34 View FIGURE 34 ).

Third pereopod stouter than fourth and fifth pereopods. Merus about 1.5 as long as ischium. Carpus about 0.5 as long as merus. Propodus about 1.7 as long as carpus, ventral margin with 7 to 13 cuspidate setae, dorsal margin without cuspidate setae. Dactylus biunguiculate, at least 0.4 as long as propodus, dorsal margin indented, with pair of cuspidate setae ( Fig. 35A, B View FIGURE 35 ).

Fourth pereopod similar to third pereopod, but thinner. Propodus with ventral margin furnished with 10 to 14 cuspidate setae, dorsal margin usually with single dorsomesial cuspidate seta on distal third, distodorsal angle usually with cuspidate seta. Dactylus dorsal margin indented, with subdistal pair of cuspidate setae ( Fig. 35C–E View FIGURE 35 ).

Fifth pereopod similar to fourth pereopod, but longer. Carpus about 0.75 as long as merus. Propodus about 1.4 as long as carpus, ventral margin furnished with 8 to 10 cuspidate setae, distal third with 4 to 6 rows of serrate setae, dorsal margin without cuspidate seta. Dactylus about 0.4 as long as propodus, dorsal margin indented, with subdistal pair of cuspidate setae ( Fig. 35F, G View FIGURE 35 ).

Male first pleopod protopodite furnished with short row of cuspidate setae on distomesial margin. Exopod at least twice as long as endopod, fringed with few plumose setae. Endopod furnished with cuspidate setae along distomesial margin, plumose setae absent, appendix interna absent. Second pleopod exopod shorter than endopod, fringed with plumose setae. Endopod elongated, straight, modified into gonopod, apex rounded, dorsomesial region with 3 rows of cuspidate setae, mesial row with longer setae, starting at level with the appendix interna and almost reaching apex of endopod, dorsal rows shorter, restricted to the distal half of endopod, not reaching mesial row distally, blocking exopod mesially, appendix interna developed, appendix masculina absent. Third to fifth pleopods protopodites furnished with few long setae on lateral margin. Endopod shorter than exopod, both fringed with plumose setae, appendix interna present on all pleopods, not reaching tip of endopod ( Fig. 37A–F View FIGURE 37 ).

Female first and second pleopod endopods slightly shorter than exopods, margins fringed with plumose setae, appendix interna absent. Third to fifth pleopod protopodites furnished with few long setae on lateral margins. Endopods shorter than exopods, both fringed with plumose setae, appendix interna absent ( Fig. 37G–K View FIGURE 37 ).

Uropod broad. Protopodite with well-developed lateral process, at least twice as long as mesial process, curving mesially, furnished distodorsally with transverse row of long simple setae, distomesial angle produced into triangular tooth. Endopod narrower than exopod, fringed with long, annulate, plumose setae, distolateral margin with few long simple setae. Exopod fringed with long, annulate, plumose setae, distal margin somewhat truncated, straight, with cluster of few long simple setae on distolateral margin, diaeresis incomplete, with 4 to 10 cuspidate setae, growing in size towards mesial margin, increasing in number with age ( Fig. 31J View FIGURE 31 ).

Remarks. Typically, males and females of Euryrhynchus share the same pleopodal formula in terms of the occurrence of the appendices internae on the pleopods 3 to 5 ( Table 2 View TABLE 2 ). Indeed, males and females of E. burchelli , E. tomasi and E. wrzesniowskii have appendices internae on pleopods 3 to 5; males and females of E. tuyuca sp. nov. have appendix interna on pleopod 3, but not on pleopods 4 and 5, whilst males and females of E. amazoniensis and E. taruman sp. nov. lack appendices internae on pleopods 3 to 5. However, Euryrhynchus pemoni is the only species in the genus in which males and females differ from each other as to the occurrence of appendices internae on pleopods 3 to 5. Males of E. pemoni present appendices internae on pleopods 3 to 5, whereas the females lack appendices internae on the pleopods 3 to 5.

The male from Cayenne (OUMNH.ZC.2013-05-0047) presents smooth cutting edges on the second pereopod fingers ( Fig. 33B, E View FIGURE 33 ) instead of having the usual pair of proximal teeth on each finger, which might be result of cheliped regeneration or an unusual variation. The male from Guyana (MZUSP 33666) is herein assigned to E. pemoni on account of the armature of the second pereopod: carpus lacking a spine on distomesial angle, and merus with a single spine distoventrally, placed on the mesial angle. However, the male (MZUSP 33666) differs from other specimens of E. pemoni in having the ocular peduncles remarkably widened in dorsal view ( Fig. 32E View FIGURE 32 , compare to Fig. 31A View FIGURE 31 ) and blunt antennal spines on the infraorbital angle ( Fig. 32E, F View FIGURE 32 ) (instead of acute antennal spines, Fig. 32B, C View FIGURE 32 ).

Prior to the present study, E. pemoni was known only from the type locality, suggesting that it was an endemic and rare species from the La Gran Sabana region ( Venezuela). The discovery of two specimens from Guyana and French Guiana showed that the species has a much broader distribution than previously assumed. Noteworthy, a recent environmental assessment in southeast Venezuela did not find specimens of Euryrhynchus ( Mora-Day et al. 2009: 100) , suggesting that the species may still be rare. Pereira’s (1985) description states that the type series was collected in the La Gran Sabana plateau (“ The material comes from La Gran Sabana, a large highland plateau in the southeast Venezuela …”), whilst the GPS coordinates provided by Pereira (06°15'N 60°01'W) actually refers to Guyana Esequiba, currently known as Cuyuni-Mazaruni ( Guyana). Judging from the data in the original labels (“... creek in La Gran Sabana road, between Sn. Rafael Town and Kama Fall, Venezuela...” and “... creek near Chirimata indigenous town, La Gran Sabana, Venezuela...”), the validity of the GPS position should be called into question. The type locality of E. pemoni is indicated on Fig. 64A View FIGURE 64 (location 1).