Euryrhynchina Powell, 1976

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) : 9

Genus Euryrhynchina Powell, 1976

Euryrhynchina Powell, 1976: 894 . Gender feminine.

Euryrhynchina — Powell 1977: 650; Holthuis 1993: 183; Pereira 1997: 3, tab. 5; De Grave 2007: 193; De Grave et al. 2008: 291; De Grave et al. 2009: 16; De Grave & Fransen 2011: 309; De Grave et al. 2015: 4; De Grave et al. 2017: 121.

Recognition characters. Rostrum smooth, non-dentate on both dorsal and ventral margins. Distomesial region of ocular peduncles produced anteriorly, reaching or overreaching distal margin of cornea. Distolateral margin of stylocerite smooth, without cluster of setae. Accessory ramus of antennule with aesthetacs restricted to distal article. Third maxilliped without arthrobranch. Third and fourth pereopod carpus without cuspidate seta on distoventral margins. Third to fifth pereopod dactyli without cuspidate setae on dorsal margins. Male second pleopod with endopod spatulate, not modified into gonopod, fringed with plumose setae, appendix masculina present. Uropodal exopod with 1 to 3 cuspidate setae on diaeresis, increasing in size towards lateral margin.

Type species. Euryrhynchina edingtonae Powell, 1976 , by monotypy.

Species included. Euryrhynchina edingtonae and Euryrhynchina puteola De Grave, Piscart, Tuekam Kayo & Anker, 2017 .

Distribution. Nigeria (Edo State, Delta State, Rivers State) and Cameroon (Littoral province) ( Powell 1976; Victor & Ogbeibu 1985; Pereira 1997; Ogbeibu & Oribhabor 2002; Ikomi et al. 2005; Olomukoro 2009; Olomukoro & Dirisu 2014; De Grave et al. 2017; present study) ( Figs. 2 , 62B , yellow and orange circles).

Remarks. The Euryrhynchina are the smallest representatives of the family Euryrhynchidae , with adult specimens up to 4.1 mm of carapace length (based on known specimens). Euryrhynchina is unique within the family in having short ocular peduncles with mesial margin produced anteriorly, absence of arthrobranch on the third maxilliped, male second pleopod with spatulate endopod, and uropodal diaeresis with up to 3 cuspidate setae. Upon the discovery of a second species in the genus, E. puteola , the presence of a cluster of setae on the distomesial region of ocular peduncles, the shape of scaphocerite and the presence of spiniform seta on third to fifth pereopod merus are no longer diagnostic for the genus, as postulated previously by Powell (1976). The West African genus Euryrhynchina and the South American genus Euryrhynchus share two exclusive diagnostic characters, such as the smooth, non-dentate rostrum and the accessory ramus of antennule with aesthetascs restricted to the distal article ( Figs. 3 A , 9 A, C , 10D–G ). Curiously, Euryrhynchina does not share a single exclusive diagnostic character with the also West African Euryrhynchoides , granted that the presence of an appendix interna on the second female pleopod (a character until now supposedly restricted to these genera, see Powell 1976: figs. 3I, 7H) also occurs in one of the Euryrhynchus species (see Euryrhynchus tuyuka sp. nov.).

Figures

FIGURE 2. Distribution map of the family Euryrhynchidae Holthuis, 1950, illustrating the known geographic distribution of the genera Euryrhynchina Powell, 1976 (yellow circles) and Euryrhynchoides Powell, 1976 (blue circles) in West Africa, and Euryrhynchus Miers, 1878 (green circles) in South America.

FIGURE 3. A–H, Euryrhynchina edingtonae Powell, 1976: male (cl 3.0 mm), Rumokoroshe, Rivers, Nigeria (USNM 171376). (A) Anterior region of the body, dorsal view; (B) Fourth sternite of pereon, median region, ventral view; (C) Fifth sternite of pereon, median region, ventral view; (D) Right second pereopod, lateral view; (E) Same, chela and carpus, dorsal (mesial) view; (F) Same, carpus and distal regionof merus, mesial view, setaeand granules omitted; (G) Left second pereopod, lateral view; (H)Same, chela and carpus, dorsal (mesial) view.

FIGURE 9. A–I, Euryrhynchus amazoniensis Tiefenbacher, 1978: (A–H) male (cl 7.5 mm), Barcelos, Amazonas, Brazil (MZUSP 20014); (I) female (cl 5.7 mm), Igarapé Japiina, Amapá, Brazil (MZUSP 21431). (A) Anterior region of the body, dorsal view; (B) Same, eye and part of frontal margin of carapace, setae omitted; (C) same, lateral view; (D) Pereon, fourth to eighth sternites, ventral view; (E) Same, fourth sternite of pereon, median region, vental view; (F) Same, fifth sternite of pereon, median region, vental view; (G) Pleon, lateral view, setae omitted; (H) Same, sixth sternite of pleon, ventral view; (I) Pleon, lateral view, setae omitted.

FIGURE 10. A–C, Euryrhynchus amazoniensis Tiefenbacher, 1978: (A, F) male holotype (cl 5.0 mm), Ilha do Careiro, southeast of Manaus, Amazonas, Brazil (ZSM 406/1); (B, G) male (cl 2.5 mm), Igarapé Santa Fé, Amazonas, Brazil (MZUSP 34520); (C) male (cl 8.4 mm), tributary of Rio Mavaca, Amazonas, Brazil (USNM 221874); (D, E, H) male (cl 7.5 mm), Barcelos, Amazonas, Brazil (MZUSP 20014). (A–C) Anterior region of the body, lateral view; (D) Right antennule, mesial view; (E) Same, ventral view; (F, G) Same, main and accessory rami, ventral view; (H) Right antena, ventral view, setae on scaphoceriteomitted.

FIGURE 62. Distribution maps for the African euryrhynchids. (A–B) Euryrhynchoides holthuisi Powell, 1976 (blue circles). (B) Euryrhynchina edingtonae Powell, 1976 (yellow circles) and Euryrhynchina puteola De Grave, Piscart, Tuekam Kayo & Anker, 2017 (orange circle).The corresponding localities for each point on the maps are indicated on the Appendix 1A–C.