Euryrhynchus Miers, 1878

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) : 16-17

Genus Euryrhynchus Miers, 1878

Euryrhynchus Miers, 1878: 662 . Gender masculine. [Placed on the Official List of Generic Names in Zoology under the name number 1274 (Opinion 518, in 1958)].

Euryrhynchus — Calman 1907: 296; Calman 1909: 93; Annandale & Kemp 1913: 245; Gordon 1935: 326; Gurney 1942: 102; Holthuis 1948: 1111; 1950a: 2; 1951: 4; 1952: 269; 1955: 76; Holthuis 1956: 68; Holthuis 1959: 102; Powell 1976: 883; Tiefenbacher 1978: 177; Kensley & Walker 1982: 2; Walker & Ferreira 1985: 265, fig. 2, tab. 2; Holthuis 1986: 589; Magnusson et al. 1987: 86; Magalhães 1988: 39; Magalhães & Walker 1988: 280; Ramos-Porto & Coelho 1990: 108; Chace 1992: 73; Chace & Bruce 1993: 3; Holthuis 1993: 185; Walker 1994: 82, tabs. 2, 4; Delgado et al. 1997: 22; Pereira 1997: 3, tab. 5; López & Pereira 1998: 77; Magalhães & Medeiros 1998: 447; Ramos-Porto & Coelho 1998: 330; Walker 2001: 566; Melo 2003: 320; Vieira 2008: 67; De Grave 2007: 194; De Grave et al. 2008: 291; De Grave et al. 2009: 17; Catarino & Zuanon 2010: 185 (tab. 1); Kemenes et al. 2010: 37; Valência & Campos 2010: 222; De Grave & Fransen 2011: 309; De Grave & Goulding 2011: 298; Botello & Alvarez 2013: 776 (tab. 1); Vogt 2013: 91; Pimentel & Magalhães 2014: 1302; Ashelby et al. 2015: 3; De Grave et al. 2015: 4; Magalhães et al. 2016: 311; Vogt 2016: 171; De Grave et al. 2017: 120; Santos et al. 2018: 23.

Euryrhynchella Balss, 1955: 1308 , 1350. Type species: Euryrhynchus wrzesniowskii Miers, 1878 . [Replacement name for Euryrhynchus Miers, 1878 ].

Euryrhynchella — Holthuis 1993: 185.

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

Type species. Euryrhynchus wrzesniowskii Miers, 1878 , by monotypy.

Species included. Euryrhynchus amazoniensis Tiefenbacher, 1978 ; Euryrhynchus burchelli Calman, 1907 ; Euryrhynchus pemoni Pereira, 1985 ; Euryrhynchus taruman sp. nov.; Euryrhynchus tomasi De Grave, 2007 ; Euryrhynchus tuyuka sp. nov.; Euryrhynchus wrzesniowskii Miers, 1878 .

Distribution. Restricted to the Amazon Region of Peru, Colombia, Venezuela, Guyana, Surinam, French Guiana and Brazil ( Tiefenbacher 1978; Pereira 1991; García-Dávila & Magalhães 2003; Melo 2003: 322, 324, 326; Valência & Campos 2010) ( Fig. 2, green circles).

Remarks. Traditionally, the species of Euryrhynchus have been differentiated mainly by the presence and distribution of spines on the second pereopod carpus and merus ( De Grave 2007: 199), with Kensley & Walker (1982) including the type of gonopod as an additional difference. All Euryrhynchus species are very similar morphologically, however during the present study several new characters are proposed to separate the species, including: (i) shape of the pterygostomial region of the carapace; (ii) shape of the transversal ridge on fourth and fifth thoracic sternites; (iii) presence and distribution of cuspidate setae on the third to fifth pereopod propodi and dactyli (although subjected to abnormal variations, see examples for E. burchelli and E. pemoni on Figs. 28, 36A, C); (iv) presence and distribution of appendices internae on the pleopods of males and females; and (v) the development of the endopod on the third to fifth pleopods. All the characters of taxonomic importance in Euryrhynchus are summarized on Table 2. We also found that a number of morphological characteristics vary ontogenetically, such as the proportions of the carpus and chela of the second pereopod, shape of the teeth on the cutting edges of the second pereopod, the number and length of the articles on the antennular accessory ramus, and the number of cuspidate setae on the uropodal diaeresis ( Figs. 10E–G, 11D, E, G, 14, 15). The development of the ocular peduncle and cornea in Euryrhynchus also seems to be influenced by ontogenetic development. In adult specimens (e.g., cl 6.0–8.0 mm), the ocular peduncles are usually longer, semi-cylindrical and reasonably separated from each other, whereas in young specimens (cl up to 4.0 mm) the ocular peduncles are shorter, much wider at base, somewhat ovate to squarish and semi-juxtaposed (cf. Figs. 9A, B, 24B, 39A, B, 55B; Magalhães 1988: figs. 1, 19). Interestingly, some adult individuals of E. pemoni from surficial water ( MZUSP 33666), E. taruman sp. nov. from subterranean water ( MZUSP 22767), and E. wrzesniowskii from both surficial ( MZUSP 26171 to 26175) and subterranean waters ( OUMNH.ZC. 2002-15 -0001) have juvenile-type ocular peduncles ( Fig. 32E, 56B, E). Furthermore, the holotype of E. wrzesniowskii ( NHM 79.21), an adult specimen from a well in French Guiana, has adult-type ocular peduncles, similar to that of a regular adult in being long and semi-cylindrical ( Fig. 56G). Therefore, adult individuals with either adult-type or juvenile-type ocular peduncles caught from both surficial and subterranean waters suggest that the shape of the ocular peduncles could be related to developmental factors rather than environmental ones.

Most previous studies used 1877 as the publication year for the generic name Euryrhynchus Miers and the specific name Euryrhynchus wrzesniowskii Miers (e.g., De Grave & Fransen 2011). However, according to Dickinson’s (2005) study on the publication dates of the Proceedings of the Zoological Society of London, 1859– 1900, the pages 653–679 in Miers were actually published in 1878 (see also Holthuis 1993: 185; and the Official List of Generic Names in Zoology—Opinion 518, in 1958).

The generic name Euryrhynchus was first coined by Nitzsch (1829) as a replacement name for Eurynorhynchus Nilsson, 1821 (type species Platalea pigmea Linnaeus, 1758 ), a genus of birds. As the overlooked name Euryrhynchus Nitzsch was a threat to the widely used name Euryrhynchus Miers, 1878 ( Crustacea )—type species Euryrhynchus wrzesniowskii Miers, 1878 –, Holthuis (1952) petitioned the International Commission on Zoological Nomenclature to use its plenary powers to suppress the name Euryrhynchus Nitzsch as an invalid emendation of Eurynorhynchus Nilsson, 1821 , and to validate the generic name Euryrhynchus Miers. Ultimately , the name Euryrhynchus Miers was placed on the Official List of Generic Names in Zoology (Opinion 518, in 1958), whereas Euryrhynchus Nitzsch was considered an incorrect subsequent spelling for Eurynorhynchus Nilsson, 1821 . Meanwhile, Balss (1955) had proposed the name Euryrhynchella Balss, 1955 (therefore, type species Euryrhynchus wrzesniowskii Miers, 1878 ) as a replacement name for Euryrhynchus Miers. However , upon the revalidation of Euryrhynchus Miers in 1958 (see above), Euryrhynchella becomes a junior synonym of Euryrhynchus Miers. The name Euryrhynchella seems not have been used except by its original author, and only listed in Holthuis (1993) and De Grave & Fransen (2011) under the synonymy of Euryrhynchus Miers.