Euryrhynchus tuyuka, Pachelle & Tavares, 2018

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) : 72-78

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.5694255
persistent identifier	https://treatment.plazi.org/id/03D987F9-FFFD-8502-A4D4-F3936300BD18
treatment provided by	Plazi
scientific name	Euryrhynchus tuyuka
status	sp. nov.

Treatment

Euryrhynchus tuyuka View in CoL sp. nov.

( Figs. 50–54 View FIGURE 50 View FIGURE 51 View FIGURE 52 View FIGURE 53 View FIGURE 54 , 65A View FIGURE 65 )

Material examined. Holotype: ♂ (cl 6.5 mm), MZUSP 16908 View Materials , Brazil, Amazonas, São Gabriel da Cachoeira , right bank of Rio Negro, Igarapé Barixia, 00°07'24.6''S 67°08'04.8''W, in submerged leaflitter, coll. J.M. Cunha, E. Trajano & J. Zuanon, 14.xii.2005 GoogleMaps . Paratypes: Brazil: 11♂ (cl 6.4– 3.4 mm) + 14♀ (cl 5.4– 3.3 mm), MZUSP 34327 , same collection data as for the holotype; 4♂ (cl 7.6– 6.8 mm), 4♀ (cl 5.8– 5.1 mm), 1♀ ov (cl 5.6 mm), MZUSP 34201 View Materials , Amazonas, São Gabriel da Cachoeira , left bank of Rio Negro , Igarapé Sabure, in submerged leaflitter, coll. J. Zuanon, J.M. Cunha & E. Trajano, 15.xii.2005 ; 2♂ (cl 6.6, 5.1 mm), 2♀ (cl 5.2, 4.3 mm), MZUSP 34202, same collection data as previous lot; 11♂ (cl 8.0– 4.3 mm), 11♀ (cl 6.4– 4.5 mm), INPA 2177, same collection data as previous lot; 3♂ (cl 7.1– 6.9 mm), 2♀ (cl 5.6, 5.1 mm), OUMNH.ZC.2016-01-026, same collection data as previous lot.

Type locality. Igarapé Barixia , São Gabriel da Cachoeira, Amazonas ( Brazil).

Distribution. Currently known only from the type locality ( Fig. 65A View FIGURE 65 , blue circle).

Description. Carapace smooth, non-setose. Branchiostegite finely granulated in large specimens, anterior margin produced beyond infra-orbital angle, branchiostegal groove weakly marked. Pterygostomial region rounded 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. 50A–C View FIGURE 50 , 51A View FIGURE 51 ).

Fourth thoracic sternite with transversal ridge slightly deepening medially, not produced. 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. 50D, E View FIGURE 50 ).

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 margins. 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, sometimes varying in length, 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 usually placed on proximal third of telson length, posterior pair usually 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 ( Figs. 50F View FIGURE 50 , 51B, C View FIGURE 51 ).

Eyes short, not overreaching proximal half of basal article of antennular peduncle. Cornea somewhat kidneyshaped in dorsal view, occupying the entire distal region and most of lateral region of ocular peduncle, basal line weakly marked, ommatidia hexagonal, ocellar spot (“ocellus”) absent. Ocular peduncles nearly immobile, basal articulation reduced, inconspicuous ( Fig. 50A–C View FIGURE 50 ).

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, with 3 to 6 free articles, increasing in number in large specimens, length of articles variable, aesthetascs restricted to distal margin of apical article ( Fig. 50A, C, G View FIGURE 50 ).

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 reaching or 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 ( Fig. 50A, C View FIGURE 50 ).

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. 50H View FIGURE 50 ).

First pereopod slender, short, carpus and chela overreaching scaphocerite when fully extended. Merus about twice as long as ischium. Carpus about same length or 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. 50I View FIGURE 50 ).

Second pereopod stout, long, pair similar in form, equal or subequal in size in both sexes. Articles varying in size with age, usually slender in small individuals and stout in large individuals. Surface of ischium to propodus (sometimes also proximal region of dactylus) finely granulated, more conspicuous in large specimens. Merus fused with ischium, distoventral angles unarmed, smooth. Carpus in adults stout in dorsal view, approximately twice as long as wide, about same length or slightly shorter than palm, distomesial angle with distal spine. Chela with transverse constriction near articulation with carpus, fingers with pair of teeth on proximal half of each cutting edge, teeth varying in shape and size with age, fingertips corneous ( Fig. 52 View FIGURE 52 ).

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 10 to 14 cuspidate setae, some more closely spaced on distal third of propodus, dorsal margin usually without cuspidate setae. Dactylus biunguiculate, at least 0.4 as long as propodus, dorsal margin indented, with single cuspidate seta, placed on mesial side ( Fig. 53A, B View FIGURE 53 ).

Fourth pereopod similar to third pereopod, but thinner. Propodus with ventral margin furnished with 8 to 14 cuspidate setae, dorsal margin usually with single dorsomesial cuspidate seta on distal third, distodorsal angle without cuspidate seta. Dactylus dorsal margin indented, with subdistal pair of cuspidate setae ( Fig. 53C, D View FIGURE 53 ).

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 7 to 13 cuspidate setae, distal third with 3 to 7 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. 53E, F View FIGURE 53 ).

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 longer than endopod, fringed with plumose setae. Endopod stout, twisted, modified into gonopod, distal half carinate dorsoventrally, tapering into triangular apex, mesial region with 3 rows of cuspidate setae, median row longer than ventral row, almost reaching distal third of endopod, dorsal row continuing on lateral margin of dorsal carina, setae curve irregularly as row approaches apex of endopod, blocking exopod mesially, mesial margin of dorsal carina with triangular lobe, appendix interna reduced, 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 only on third (rarely also fourth) pleopod, not reaching tip of endopod ( Fig. 54A–F View FIGURE 54 ).

Female first and second pleopod endopods shorter than exopods, margins smooth or fringed with fewer plumose setae than exopod, appendix interna present on second pleopod. Third to fifth pleopod protopodites furnished with few long setae on lateral margins. Endopods shorter than exopods, both fringed with plumose setae, appendix interna present only on third (rarely also fourth) pleopod, not reaching tip of endopod ( Fig. 54G–K View FIGURE 54 ).

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 rounded or angular (sometimes produced into small 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 5 to 9 cuspidate setae, growing in size towards mesial margin, increasing in number with age ( Fig. 50J View FIGURE 50 , 51D View FIGURE 51 ).

Etymology. The specific epithet “ tuyuka ”, a noun in apposition, refers to the Tuyuka indigenous tribe from Amazonas State ( Brazil), who perform the ceremonial dance "Dasia Basa" (= shrimp dance) during certain rituals.

Remarks. Euryrhynchus tuyuka sp. nov. resembles E. amazoniensis and E. taruman sp. nov. in having (i) the second pereopod carpus with a distal spine on the distomesial angle ( Fig. 52D View FIGURE 52 ), (ii) the third pereopod dactylus with single cuspidate seta on the dorsal margin, placed on mesial side ( Fig. 53B View FIGURE 53 ), (iii) the fifth pereopod dactylus with pair of cuspidate setae on the dorsal margin ( Fig. 53F View FIGURE 53 ), (iv) the male gonopod stout, twisted, not overreaching exopod, with appendix interna inconspicuous ( Fig. 54B, C View FIGURE 54 ), and (v) the fourth and fifth pleopods with endopod overreaching mid-length of exopod ( Fig. 54E, F, J, K View FIGURE 54 ). Nevertheless, E. tuyuka sp. nov. can be readily recognized by the presence of appendices internae on the second and third (rarely also fourth) pleopods of males and females, Fig. 54B–D, H, I View FIGURE 54 (versus appendix interna present only on second male pleopod, whereas the female pleopods lack appendix interna in both E. amazoniensis and E. taruman sp. nov., Figs. 17 View FIGURE 17 , 43 View FIGURE 43 ). Euryrhynchus tuyuka sp. nov. further differs from E. amazoniensis in the pterygostomial region of the carapace being rounded or angular ( Figs. 50C View FIGURE 50 , 51A View FIGURE 51 ), not produced anteriorly into a sharp tooth as in E. amazoniensis (cf. Figs. 9C View FIGURE 9 , 10A–C View FIGURE 10 ). Euryrhynchus tuyuka sp. nov. also differs from E. taruman sp. nov. in having the second pereopod carpus stout in dorsal view, about 1.5–2 times as long as wide in large specimens, Fig. 52 View FIGURE 52 (versus second pereopod carpus elongated, about 3 or more times as long as wide in large specimens in E. taruman sp. nov., Fig. 40 View FIGURE 40 ).

Tiefenbacher (1978) reported specimens of E. amazoniensis from two localities near São Gabriel da Cachoeira (previously named Uaupés, see localities 3 and 4 in Tiefenbacher, 1978: 179): ZSM 407/10 and ZSM 407/11 ( Fig. 62 View FIGURE 62 , green circles, locations 18 and 19). Because São Gabriel da Cachoeira is near the type locality of E. tuyuca n. sp. (Igarapé Barixia), we expected that these specimens would probably also belong to E. tuyuca n. sp. However, examination of the ZSM specimens revealed that all of them indeed belong to E. amazoniensis , suggesting that E. tuyuka sp. nov. might be a geographically restricted species.