Family Euryrhynchidae Holthuis, 1950

Euryrhynchidae Holthuis, 1950a: 2 .

Euryrhynchidae—Pereira & García 1995: 131; Martin & Davis 2001: 46, 72; De Grave 2007: 194; Magalhães & Pereira 2007: 112, tabs. 1–4; Bracken et al. 2009: 297, tab. 1, fig. 2; De Grave et al. 2009: 16; Mora-Day et al. 2009: 90; Shibuya et al. 2009: 470; Valência & Campos 2010: 222; De Grave & Fransen 2011: 309; Botello & Alvarez 2013: 775; Kou et al. 2013: 502, tab. 1, figs. 1, 2 (tree); Vogt 2013: 88; De Grave & Goulding 2011: 288, tabs. 1–2; Moscoso 2012: 43; Pimentel & Magalhães 2014: 1302; Ashelby et al. 2015: 4, tab. 1; De Grave et al. 2015: 4, figs. 2, 5; Magalhães et al. 2016: 304; Vogt 2016: 171; Wehrtmann et al. 2016: 271; De Grave et al. 2017: 121; Santos et al. 2018: 23.

Euryrhynchinae Holthuis, 1950a: 2.

Euryrhynchinae—Holthuis 1951: 3; Chace 1954: 323; Holthuis 1955: 43, 76; Holthuis 1959: 100; Holthuis 1966: 6; Powell 1976: 884; Powell 1977: 650; Tiefenbacher 1978: 177, fig. 1 (map); Pereira 1985: 619; Holthuis 1986: 591; Magalhães 1988: 39; Ramos-Porto & Coelho 1990: 108; Pereira 1991: 83; Chace 1992: 71; Bruce 1993: 41; Chace & Bruce 1993: 3; Holthuis 1993: 20, 91, 183; Delgado et al. 1997: 22; Pereira 1997: 2, tabs. 1, 4–6, fig. 1 (map); López & Pereira 1998: 77; García-Dávila & Magalhães 2003: 665; Melo 2003: 320; Vieira 2003: 57; De Grave et al. 2008: 289, tab. 1.

Euryrhychinae—Vieira 2003: 59 [lap. cal.].

Euryrhynchindae—Vieira 2008: 67 [lap. cal.].

Euryrhynchinidae—Pereira 1997: 36; Vieira 2008: 68, tab. 5.1 [lap. cal.].

Euryrhynchynidae—Vieira 2008: 18 [lap. cal.].

Euryrynchidae—Ikomi et al. 2005: tab. 2 [lap. cal.].

Euryrhynchydae—Olomukoro 2009: 310, tabs. 1, 4 [lap. cal.].

Recognition characters. Eyes short, not reaching distal margin of first article of antennular peduncle; peduncle poorly articulated, almost immobile; cornea pigmented, ommatidia hexagonal, ocellar spot (“ocellus”) absent. Rostrum short, triangular in dorsal view, not reaching or slightly overreaching distal margin of cornea. Antennal spine present. Branchiostegal, hepatic and epigastric spines absent. Branchiostegite produced anteriorly, overreaching infraorbital angle. Branchiostegal groove present, poorly delimited. Stylocerite broadly rounded or slightly angular, not produced into lateral spine. First article of antennular peduncle with distolateral margin produced into acute tooth. Upper antennular flagellum with accessory ramus fused to main ramus at base by single article; accessory ramus much shorter and broader than main ramus. Mandible without palp. Maxillipeds with well developed exopods. Third maxilliped without pleurobranch; arthrobranchs varying from 0–2. Pereopods without exopods; second pereopod with 2 teeth on proximal region of each cutting edge, surface of ischium to dactylus finely granulated (except in Euryrhynchus burchelli); dactyli of third to fifth pereopods biunguiculate. First pleopod of males and females without appendix interna. Uropodal protopodite with lateral process more developed than mesial process, curving mesially towards endopod; both endopod and exopod fringed with long, annulate, plumose setae. Telson broad, not tipping towards distolateral region; distal margin broadly rounded, furnished with long, annulate, plumose setae; dorsal surface with 2 pairs of cuspidate setae; distolateral angle with pair of cuspidate setae, mesial seta about twice as long as lateral seta.

Genera included. Euryrhynchina Powell, 1976, Euryrhynchoides Powell, 1976 and Euryrhynchus Miers, 1878 .

Distribution. Freshwater habitats in tropical South America ( Euryrhynchus) and West Africa ( Euryrhynchoides and Euryrhynchina) (Fig. 2). South America: Peru, Colombia, Venezuela, Guyana, Suriname, French Guiana and Brazil (Tiefenbacher 1978; Pereira 1991; García-Dávila & Magalhães 2003; Valência & Campos 2010). West Africa: Sierra Leone, Nigeria and Cameroon (Powell 1976; Nwadiaro 1984; De Grave et al. 2017).

Remarks. The euryrhynchid genera are easily distinguishable from one another, not only in rostral morphology, but especially so in respect to the morphology of the male second pleopod. In Euryrhynchina the appendix masculina is individualized (as in the norm in carideans) (see Powell 1976: fig. 7J, K), whereas in Euryrhynchoides and Euryrhynchus an appendix masculina is lacking and the endopod modified into a complex structure (herein termed gonopod), which varies morphologically in both genera. In Euryrhynchoides the gonopod is twisted and longer than the exopod, with an accessory branch on the dorsal region and no discernible appendix interna (Fig. 5D, E [arrows]). In Euryrhynchus the gonopod is either stout, twisted, and shorter than the exopod ( E. amazoniensis, E. taruman sp. nov. and E. tuyuka sp. nov.) (Figs. 17B–E, 23) or elongated, straight, and longer than the exopod ( E. burchelli, E. pemoni, E. tomasi and E. wrzesniowskii) (Fig. 29B, C, 30). In Euryrhynchus, both forms of gonopods do have an appendix interna on the mesial margin of the gonopod, but no accessory branch as in Euryrhynchoides .

Several authors have speculated about the origin and evolution of the gonopod in euryrhynchids. Gordon (1935) was the first to describe and illustrate the pleopods of an euryrhynchid ( E. wrzesniowskii), considering the gonopod as an elongated endopod with a reduced appendix interna but devoid of appendix masculina. Gordon’s (1935) definition of the gonopod was used subsequently by Holthuis (1950a, 1951, 1955). However, the discovery of the genera Euryrhynchina and Euryrhynchoides led Powell (1976) to the conclusion that the gonopod in Euryrhynchus is actually the appendix masculina in an endopod lacking its distal part, but provided with appendix interna. Furthermore, Powell (1976) speculated that the biramous gonopod in Euryrhynchoides is formed by the modification of both endopod and appendix masculina (= accessory branch located dorsally, Fig. 5D, E [arrows]), with the appendix interna lacking. Kensley & Walker (1982) were the first to compare both forms of gonopods in Euryrhynchus, referring to the gonopod of E. amazoniensis as an endopod ( sensu Gordon 1935), although mentioning the suggestion of Chace (pers. comm. to Kensley and Walker) that the real endopod of Euryrhynchus was lost and replaced by the appendix masculina, thus supporting, in part, Powell’s (1976) hypothesis. The idea that the gonopod in Euryrhynchus represents a modification of the endopod (instead of a developed appendix masculina) has been accepted by numerous subsequent authors, such as Pereira (1991, 1997), García-Dávila & Magalhães (2003), De Grave (2007) and Valência & Campos (2010). Mistakenly, García-Dávila & Magalhães (2003) refer to the appendix interna on the gonopod of E. amazoniensis as a reduced appendix masculina. De Grave (2007) speculated that the appendix masculina ( sensu Powell 1976; herein termed accessory branch) on the gonopod of Euryrhynchoides could be the result of a modification on the appendix interna (individualized on the gonopod of Euryrhynchus) or even the appendix interna and masculina coalesced. Typically, the appendix masculina carries cuspidate setae distally (cf. Pereira 1997: fig. 34; Powell 1976: fig. 7J, K) and is, as a rule, inserted on the mesial surface of the endopod, thus located between the appendix interna and the endopod. In our perspective the presence of cuspidate setae on the mesial surface of the gonopod in Euryrhynchoides and Euryrhynchus (Figs. 5D, E, 17B–E, 23, 29B, C, 30) may be regarded as an indication that the gonopod is formed by the coalescenced appendix masculina and endopod. In Euryrhynchoides, the accessory branch on the gonopod was referred as to “appendix masculina” by Powell (1976). We instead use the term “accessory branch”, since it can be recognized neither as an appendix interna nor as an appendix masculina due to the lack of cincinulli and cuspidate setae, respectively, but possessing instead a series of ridges on the apical region (Fig. 5D, E).

The branchial formula in Euryrhynchidae is similar among the genera, except for the number of arthrobranchs on the third maxilliped. In Euryrhynchina the third maxilliped has no arthrobranchs; in Euryrhynchoides there are 2 arthrobranchs; and in Euryrhynchus there is only 1 arthrobranch (Table 1).

The fourth and fifth thoracic sternites in Euryrhynchidae present a transversal carina, whose median region varies in shape. In Euryrhynchoides the carina on the fourth sternite bears a well developed lanceolate median process (Fig. 5B), whereas the carina on the fifth sternite presents a reduced lobular process (Fig. 5C). In Euryrhynchina the carinae of both sternites carry a reduced lobular process (Fig. 3 B, C), whereas in Euryrhynchus the median process on the carinae of both sternites can be absent or variable in size, ranging from a low to a distinct, acute process (not as strong as in Euryrhynchoides) (Figs. 9D–F, 18D, E, 24D, E, 31D, E, 38D, E, 45D, E, 50D, E, 55D, E).

Taxonomic key for identification of genera and species of Euryrhynchidae

1a. Ocular peduncles with distomesial region produced anteriorly, reaching or overreaching distal margin of cornea (Fig. 3A). Third maxilliped without arthrobranch. Third to fifth pereopod dactyli without cuspidate setae on dorsal margins (Fig. 4B, D, E, G). Male second pleopod with endopod spatulate, not modified into gonopod, fringed with plumose setae, appendix masculina present (Powell, 1976: fig. 7J, K)............................................ 2 [ Euryrhynchina Powell, 1976]

1b. Ocular peduncles with distomesial region not produced anteriorly, not reaching distal margin of cornea (Figs. 9A, B, 56). Third maxilliped with at least 1 arthrobranch. Third to fifth pereopod dactyli with at least 1 cuspidate seta on dorsal margin (Fig. 16B, E, F, I). Male second pleopod with endopod not spatulate, modified into gonopod, fringed with series of cuspidate setae mesially, appendix masculina lacking (Figs. 5D, E, 17B–E, 23, 29B, C, 30)........................................................................................ 3 [ Euryrhynchoides Powell, 1976 and Euryrhynchus Miers, 1878]

2a. Ocular peduncles with distomesial region setose (Fig. 3 A). Scaphocerite with lateral tooth greatly overreaching distal margin of blade (Fig. 3 A). Third to fifth pereopod merus with cuspidate seta on lateral margin (Fig. 4 A, C, F). Male second to fifth pleopods with appendix interna........................................... Euryrhynchina edingtonae Powell, 1976

2b. Ocular peduncles with distomesial region non-setose (De Grave et al. 2017: fig. 1A). Scaphocerite with lateral tooth not reaching distal margin of blade (De Grave et al. 2017: fig. 1E). Third to fifth pereopod merus without cuspidate seta on lateral margin (De Grave et al. 2017: fig. 3E, G). Male second to fifth pleopods without appendix interna.................................................................... Euryrhynchina puteola De Grave, Piscart, Tuekam Kayo & Anker, 2017

3a. Rostrum dentate dorsally. Accessory ramus of antennule with aesthetacs present on more than one article (Fig. 5 A). Third maxilliped with 2 arthrobranchs. Third and fourth pereopod carpus with cuspidate seta distoventrally (Fig. 7 A, C). Male gonopod with accessory branch mesially, appendix interna lacking (Fig. 5D, E)......... Euryrhynchoides holthuisi Powell, 1976

3b. Rostrum smooth, non-dentate dorsally. Accessory ramus of antennule with aesthetacs restricted to the distal article (Fig. 1 0D– G, 18H). Third maxilliped with 1 arthrobranch. Third and fourth pereopod carpus without cuspidate seta distoventrally (Fig. 16 A, D). Male gonopod without accessory branch mesially, appendix interna present (Figs. 17B–E, 23F, 29B, C, 30E).................................................................................... 4 [ Euryrhynchus Miers, 1878]

4a. Second pereopod merus with distoventral angles unarmed, smooth (Fig. 14C). Third pereopod dactylus with 1 cuspidate seta on the dorsal margin, placed on mesial side (Fig. 16B). Fourth pereopod propodus usually without cuspidate seta on distodorsal angle (Fig. 16E, F)................................................................................. 5

4b. Second pereopod merus with 1 or 2 spines on the distoventral angles (Figs. 25D, 34C). Third pereopod dactylus with pair of cuspidate setae on the dorsal margin (Fig. 27B). Fourth pereopod propodus usually with cuspidate seta on distodorsal angle (Fig. 27D)........................................................................................... 8

5a. Second pereopod carpus with distomesial angle unarmed, smooth (Fig. 57D). Fifth pereopod dactylus with 1 cuspidate seta on dorsal margin, placed on lateral side (Fig. 59G, H). Male gonopod elongated, straight, overreaching exopod, appendix interna distinct (Fig. 60B, C, L). Fourth and fifth pleopods with endopod short, not reaching half length of exopod, appendix interna reaching or overreaching distal margin of endopod (Fig. 60E, F, J, K)............ Euryrhynchus wrzesniowskii Miers, 1878

5b. Second pereopod carpus with spine on the distomesial angle (Figs. 14C, 20G). Fifth pereopod dactylus with pair of cuspidate setae on dorsal margin (Fig. 16I). Male gonopod stout, twisted, not overreaching exopod, appendix interna inconspicuous (Fig. 17B–E, 23). Fourth and fifth pleopods with endopod long, reaching or overreaching half length of exopod, appendix interna (if present) not reaching distal margin of endopod (Fig. 17G, H, L, M).............................................. 6

6a. Appendix interna present on second and third (rarely also fourth) pleopods of both sexes (Fig. 54B, D, H, I).......................................................................................... Euryrhynchus tuyuka sp. nov.

6b. Appendix interna present only on second pleopod of male, female without appendix interna on pleopods (Figs. 17, 23)... 7

7a. Carapace with pterygostomial region produced anteriorly into acute, triangular tooth (Figs. 9C, 10 A –C, 18 A, B). Large individuals with second pereopod carpus stout in dorsal view, up to 2 times as long as wide (Figs. 14B, 15B).............................................................................. Euryrhynchus amazoniensis Tiefenbacher, 1978

7b. Carapace with pterygostomial region rounded or broadly angular, not produced anteriorly (Figs. 38C, 39C, 41A). Large individuals with second pereopod carpus elongated in dorsal view, about 2.5 to 3 times as long as wide (Fig. 40B, E)..................................................................................... Euryrhynchus taruman sp. nov.

8a. Second pereopod merus with single spine, placed on the distomesial angle (Fig. 34C, E). Third to fifth pleopods of female without appendix interna (Fig. 37I –K)......................................... Euryrhynchus pemoni Pereira, 1985

8b. Second pereopod merus with pair of spines, one on each distoventral angle (Figs. 25D, 46D). Third to fifth pleopods of female with appendix interna (Fig. 29I –K)....................................................................... 9

9a. Second pereopod carpus with spine on the distomesial angle (Fig. 25D). Second pereopod without fine granules on surface of articles (Fig. 25). Fourth sternite of pereon with transversal ridge produced into low, broad lobe medially (Fig. 24D)............................................................................. Euryrhynchus burchelli Calman, 1907

9b. Second pereopod carpus with distomesial angle unarmed, smooth (Fig. 46D). Second pereopod with fine granules at least on surface of carpus and propodus (Fig. 46). Fourth sternite of pereon with transversal ridge produced into prominent, triangular lobe medially (Fig. 45D).................................................. Euryrhynchus tomasi De Grave, 2007