INTRODUCTIONTop

Phoxocephalidae Sars, 1891 is a marine benthic family living mostly buried within the substrate and comprising about 365 species grouped into 80 genera (Barnard and Drummond 1978Barnard J.L., Drummond M.M. 1978. Gammaridean Amphipoda of Australia, part III: The Phoxocephalidae. Smith. Contrib. Zool. 245: 1-551., Horton et al. 2019Horton T., Lowry J.K., De Broyer C., et al. 2019. World Amphipoda Database. Phoxocephalidae G.O. Sars, 1891. Accessed through: World Register of Marine Species on 26/9/2019). It is widely distributed bathymetrically and most of its diversity can be found in the Southern Hemisphere deep sea (Hartman 1955Hartman O. 1955. Quantitative survey of the benthos of San Pedro Basin, Southern California. Part I. Preliminary results. Allan Hancock Pac Exped. 19: 1-185., Alonso de Pina et al. 2008Alonso de Pina G.M., Rauschert M., De Broyer C. 2008. A catalogue of the Antarctic and sub-Antarctic Phoxocephalidae (Crustacea: Amphipoda: Gammaridea) with taxonomic, distribution and ecological data. Zootaxa 1752: 1-40., Senna 2010Senna A.R. 2010. A new genus and five new species of Phoxocephalidae (Crustacea: Amphipoda) from the south-east Brazilian deep sea. J. Nat. Hist. 44: 2075-2118.). The family is the fifth most speciose amphipod taxa (Arfianti et al. 2018Arfianti T., Wilson S., Costello M.J. 2018. Progress in the discovery of amphipod crustaceans. PeerJ 6: e5187.) and can be distinguished by the following characters: head with visor-like rostrum, not cylindrical; antennae 1-2 of haustorioid form, with multiarticulate accessory flagellum; gnathopods 1-2 subchelate or chelate; pereopod 6 usually elongate; pereopod 7 short, with basis expanded posteroventrally, strongly distinct in size and shape from pereopod 6; uropod 3 biramous; and telson short to long, cleft (Barnard and Drummond 1978Barnard J.L., Drummond M.M. 1978. Gammaridean Amphipoda of Australia, part III: The Phoxocephalidae. Smith. Contrib. Zool. 245: 1-551., 1982Barnard J.L., Drummond M.M. 1982. Gammaridean Amphipoda of Australia, Part V: Superfamily Haustorioidea. Smith. Contrib. Zool. 360: 1-148.). Its external morphology is an adaptation to its ecological habits as burrowers, having characters like a broad rostrum and developed pereopods with stout setae (Alonso and Chiesa 2014Alonso G.M., Chiesa I.L. 2014. Phoxocephalidae. In: Roig-Juñent S., Claps L.E., Morrone J.J. (eds), Biodiversidad de Artropodos Argentinos - Vol. 3. INSUE-UNT, San Tucuman, Argentina, pp. 205-213.).

In the past, the genera of Phoxocephalidae were grouped into nine subfamilies by Barnard and Drummond (1978)Barnard J.L., Drummond M.M. 1978. Gammaridean Amphipoda of Australia, part III: The Phoxocephalidae. Smith. Contrib. Zool. 245: 1-551.. Over time, the status and establishment of new subfamilies were proposed and discussed to solve some questions regarding divergences between the genera (Gurjanova 1977Gurjanova E.F. 1977. Some new data in taxonomy of family Phoxocephalidae sensu lato (Amphipoda, Gammaridea). Report I. Proc USSR Acad Sci. 21: 67-87., Barnard and Karaman 1991Barnard J.L., Karaman G. 1991. The families and genera of marine gammaridean Amphipoda (except marine Gammaroidea). Part 2. Rec. Aust. Mus. 13: 419-866., Jarret and Bousfield 1994aJarret N.E., Bousfield E.L. 1994a. The amphipod superfamily Phoxocephaloidea on the pacific coast of North America. Family Phoxocephalidae. Part I. Metharpiniinae, new subfamily. Amphipacifica 1: 58-140., bJarret N.E., Bousfield E.L. 1994b. The amphipod superfamily Phoxocephaloidea on the pacific coast of North America. Family Phoxocephalidae. Part II. Subfamilies Pontharpiniinae, Paharpiniinae, Brolginae, Phoxocephalinae, and Harpiniinae. Systematics and distributional ecology. Amphipacifica 3: 71-150.). However, through cladistic analysis, Taylor and Poore (2001)Taylor J., Poore G.C.B. 2001. Descriptions of new species of Birubius (Amphipoda: Phoxocephalidae) from Australia and Papua New Guinea with comments on the Birubius-Kulgaphoxus-Tickalerus-Yan complex. Mem. Mus. Vic. 58: 255-295. failed to obtain support for the monophyly of the proposed subfamilies. According to Alonso de Pina et al. (2008)Alonso de Pina G.M., Rauschert M., De Broyer C. 2008. A catalogue of the Antarctic and sub-Antarctic Phoxocephalidae (Crustacea: Amphipoda: Gammaridea) with taxonomic, distribution and ecological data. Zootaxa 1752: 1-40., Barnard and Drummond’s division of subfamilies must not be recognized until new phylogenetic studies are done.

The current classification of Phoxocephalidae is based on purely morphological criteria (De Broyer et al. 2007De Broyer C., Lowry J.K., Jazdzewski K., et al. 2007. Census of Antarctic Marine Life. Synopsis of the Amphipoda of the Southern Ocean. Part. 1. Catalogue of the Gammaridean and Corophiidean Amphipoda (Crustacea) of the Southern Ocean with distribution and ecological data. Bull. Inst. R. Sci. Nat. Belg. 77: 1-325., Senna and Souza-Filho 2011Senna A.R., Souza-Filho J.F. 2011. A new species of Pseudharpinia (Amphipoda: Haustorioidea: Phoxocephalidae) from Southeastern Brazilian continental shelf. Nauplius 19: 7-16., Lowry and Myers 2017Lowry J.K., Myers A.A. 2017. A Phylogeny and Classification of the Amphipoda with the establishment of the new order Ingolfiellida (Crustacea: Peracarida). Zootaxa 4265: 1-89.), grouping all genera into two subfamilies: Harpiniinae Barnard and Drummond, 1978, diagnosed mainly by pereopod 5 with a narrow basis; and Phoxocephalinae Sars, 1891, characterized by pereopod 5 with a stout basis. Although we follow the most recent classification within the family, the World Amphipoda Database (Horton et al. 2019Horton T., Lowry J.K., De Broyer C., et al. 2019. World Amphipoda Database. Phoxocephalidae G.O. Sars, 1891. Accessed through: World Register of Marine Species on 26/9/2019) continues to use the classical division using the old subfamilies. As recent authors have been accepting only two subfamilies (Andrade and Senna 2019aAndrade L.F., Senna A.R. 2019a. Two new species of Cephalophoxoides Gurjanova, 1977 (Crustacea: Amphipoda: Phoxocephalidae) from southeastern Brazil, with comments on the taxonomic status of the genus. Zootaxa 4712: 531-551., bAndrade L.F., Senna A.R. 2019b. First record of the genus Limnoporeia Fearn-Wannan, 1968 (Crustacea: Amphipoda: Phoxocephalidae) from the Atlantic Ocean, with description of a new species. J. Nat. Hist. 53: 2517-2531., 2020Andrade L.F., Senna A.R. 2020. A novel species of Heterophoxus Shoemaker, 1925 (Crustacea, Amphipoda, Phoxocephalidae) from southeast and southern Brazil, with an identification key to world species of the genus. Eur. J. Taxon. 592: 1-16.), it is suggested that the current classification should be updated in the database.

The establishment of a new genus can be somewhat problematic, especially in the family Phoxocephalidae. Taylor (2006)Taylor J. 2006. A new species of Leongathus from the Tasman Sea collected during the 2003 NORFANZ Expedition (Crustacea: Amphipoda: Phoxocephalidae). Mem. Mus. Vic. 63: 207-213. noticed this issue and highlighted the past works within the family when several new genera were established based on recombinations of known characters instead of newly or advanced ones, raising the number of monotypic genera. Furthermore, many species achieve the status of a genus or subfamily due to a few unusual characteristics, resulting in several paraphyletic taxa.

Atlantiphoxus n. gen. seems to be close to the genus Fuegiphoxus Barnard and Barnard, 1980, which was established with Parharpinia fuegiensis Schellenberg, 1931 as the type species. In the same work, the authors described F. abjectus Barnard and Barnard, 1980, F. inutilus Barnard and Barnard, 1980, and Pontharpinia uncinata Chevreux, 1912, which was provisionally assigned to the newly proposed genus and afterwards redescribed and confirmed as belonging to Fuegiphoxus (Chiesa and Alonso, 2011). Both the genera Parharpinia and Pontharpinia, plus Protophoxus K.H. Barnard, 1930, Trichophoxus K.H. Barnard, 1930 and Metharpinia Schellenberg, 1931, were considered a synonym of Protophoxus by J.L. Barnard (1960). Barnard and Drummond (1976)Barnard J.L., Drummond M.M. 1976. Classification of five genera of Phoxocephalidae (Marine Amphipoda). Proc. Biol. Soc. Wash. 88: 515-548. examined individuals of the type species belonging to the genera previously mentioned (except Metharpinia) and reconsidered their validity based on the analysis of 250 known characters and some new ones.

Considering the story of reallocations over the years between these phoxocephalid genera cited above, it is clear to see that Parharpinia and Pontharpinia were treated as close taxa, even being synonymized within Paraphoxus. Moreover, one species from each genus was removed from its current assigned genera to Fuegiphoxus, which was raised on the basis of the following divergences from Paraphoxus: antenna 2, article 4 with weak division of the stout setae rows and proximal position of the dorsal notch; mandibular molar with elongation of the third stout seta; maxilla 1, inner plate with 4 setae; maxilliped, inner plate with 1 apical stout seta; gnathopod 1, carpus elongate; gnathopod 2 significantly enlarged; gnathopod 2, carpus cryptic; pereopod 3-4, merus and carpus with well-developed facial setae; pereopod 7, apical digitation of propodus; and uropod 1-2, rami with lowered flexibility of the apical nail. To allocate F. uncinatus, Chiesa and Alonso (2011)Chiesa I.L., Alonso G.M. 2011. Redescription and generic assignment of Fuegiphoxus uncinatus (Chevreux, 1912) (Crustacea, Amphipoda, Phoxocephalidae). Zoosystema 33: 219-233. made an emended diagnosis of the genus by adding the following character states: maxilliped, inner plate with 1 or 2 apical stout setae; gnathopod 2, carpus subcryptic to cryptic; epimeral plate 3, posteroventral corner rounded or with hook; telson bearing two or three apical stout setae.

Although one assumes the new genus has a relationship with Fuegiphoxus and Parharpinia, herein, we decided to establish a new genus instead of making an emended diagnosis of the morphologically closest taxon, especially because of many noteworthy combinations and exclusive characters that will be discussed below.

MATERIALS AND METHODSTop

The material examined was collected between 1970 and 1971 by R/V Prof. W. Besnard at 224 and 500 m depth off Brazil’s southeastern coast in the states of Rio de Janeiro and São Paulo. The campaign was organized by the Instituto Oceanográfico of the Universidade de São Paulo (IO - USP), within the Mini Biological Trawl (MBT) project. All specimens were preserved in 70% ethanol and deposited in the Crustacea Collection of the Universidade do Estado do Rio de Janeiro (UERJ). For the taxonomic study, the appendages were dissected and mounted in glycerin gel slides, drawn under an optical microscope with a Motic BA-310 camera lucida and digitized with CorelDRAW 2018. The setal/spine classification adopted in this paper follows Garm and Watling (2013)Garm A., Watling L. 2013. The crustacean integument: setae, setules, and other ornamentation. In: Watling T., Thiel M., (eds). The Natural History of the Crustacea. Functional Morphology and Diversity. Oxford Univ. Press, Oxford, pp. 167-198.. The nomenclature of the gnathopod palm is based on Poore and Lowry (1997)Poore A.G.B., Lowry J.K. 1997. New ampithoid amphipods from Port Jackson, New South Wales, Australia (Crustacea: Amphipoda: Ampithoidae). Invertebr. Taxon. 11: 897-941..

RESULTSTop

Order Amphipoda Latreille, 1816
Suborder Amphilochidea Boeck, 1871
Superfamily Haustorioidea Stebbing, 1906
Family Phoxocephalidae Sars, 1891

Diagnosis (after Barnard and Karaman, 1991Barnard J.L., Karaman G. 1991. The families and genera of marine gammaridean Amphipoda (except marine Gammaroidea). Part 2. Rec. Aust. Mus. 13: 419-866.). Rostrum visor-like or absent, not cylindrical; ventral cephalic cheek weak or absent. Article 3 of antenna 1 short; article 4 of antenna 2 with facial stout setae. When rostrum reduced or absent, facial stout setae occurring on article 4 of antenna 2 or articles 4-5 of pereopods 5-6. Right incisor broad and 3+ toothed; mandibular palp article 3 with up to 2 sets of outer setae closely contiguous on opposite faces, never in serial ranks, apex bevelled, all other setae dominantly apical; molar, if triturative, of cup-shaped form, otherwise “spinose” or simple. Inner plate of maxilla 1 never pointed, never with more than 2 fully medial setae, other setae apical of absent. Coxae regular. Pereopod 5 with facial stout setae on articles 4-5. Pereopod 7 distinct from pereopods 5-6, much shorter than 6, article 2 broadly expanded in free, plate-like lobe. Epimeral plate 1 well developed. Peduncles of pleopods longer than wide. Rami of uropods 1-2 styliform. Uropod 3 biramous. Telson deeply cleft.

Subfamily Phoxocephalinae Sars, 1891

Diagnosis. Pereopod 5, basis broad, expanded.

Composition of the subfamily. The subfamily is composed of 270 species grouped in 70 genera (Horton et al. 2019Horton T., Lowry J.K., De Broyer C., et al. 2019. World Amphipoda Database. Phoxocephalidae G.O. Sars, 1891. Accessed through: World Register of Marine Species on 26/9/2019) + 1 new genus: Atlantiphoxus n. gen. (1 species); Baliphoxus Ortiz and Lalana, 1999 (1 species); Bathybirubius Senna, 2010 (1 species); Beringiaphoxus Jarrett and Bousfield, 1994 (1 species); Birubius Barnard and Drummond, 1976 (48 species); Booranus Barnard and Drummond, 1978 (4 species); Brolgus Barnard and Drummond, 1978 (7 species); Cephalophoxoides Gurjanova, 1977 (10 species); Cephalophoxus Gurjanova, 1977 (1 species); Cunmurra Barnard and Drummond, 1978 (1 species); Diogodias Barnard and Drummond, 1978 (2 species); Elpeddo Barnard and Drummond, 1978 (1 species); Eobrolgus Barnard, 1979 (3 species); Eusyrophoxus Gurjanova, 1977 (1 species); Eyakia Barnard, 1979 (5 species); Foxiphalus Barnard, 1979 (12 species); Fuegiphoxus Barnard and Barnard, 1980 (4 species); Ganba Barnard and Drummond, 1978 (1 species); Grandifoxus Barnard, 1979 (15 species); Griffithsius Jarrett and Bousfield, 1994 (1 species); Hopiphoxus Barnard and Drummond, 1978 (1 species); Indophoxus Dang and Le, 2005 (1 species); Japara Barnard and Drummond, 1978 (1 species); Jerildaria Barnard and Drummond, 1978 (1 species); Joubinella Chevreux, 1908 (6 species); Kondoleus Barnard and Drummond, 1978 (1 species); Kotla Barnard and Drummond, 1978 (1 species); Kulgaphoxus Barnard and Drummond, 1978 (3 species); Kuritus Barnard and Drummond, 1978 (1 species); Leongathus Barnard and Drummond, 1978 (2 species); Leptophoxoides Barnard, 1962 (2 species); Leptophoxus G. O. Sars, 1891 (1 species); Limnoporeia Fearn-Wannan, 1968 (10 species); Linca Alonso de Pina, 1993 (1 species); Majoxiphalus Jarrett and Bousfield, 1994 (1 species); Mandibulophoxus Barnard, 1957 (8 species); Matong Barnard and Drummond, 1978 (1 species); Mesophoxus Gurjanova, 1977 (1 species); Metaphoxoides Ledoyer, 1968 (3 species); Metaphoxus Bonnier, 1896 (8 species); Metharpinia Schellenberg, 1931 (10 species); Microphoxus Barnard, 1960 (5 species); Palabriaphoxus Gurjanova, 1977 (2 species); Parafoxiphalus Alonso de Pina, 2001 (1 species); Parajoubinella Gurjanova, 1977 (1 species); Paramesophoxus Gurjanova, 1977 (1 species); Parametaphoxus Gurjanova, 1977 (3 species); Paraphoxus G. O. Sars, 1891 (14 species); Parharpinia Stebbing, 1899 (4 species); Phoxocephalus Stebbing, 1888 (2 species); Phoxorgia Barnard and Barnard, 1980 (1 species); Pontharpinia Stebbing, 1897 (5 species); Protophoxus K.H. Barnard, 1930 (1 species); Pseudfoxiphalus Andres, 1991 (1 species); Rhepoxynius Barnard, 1979 (18 species); Rikkarus Barnard and Drummond, 1978 (1 species); Ringaringa Barnard and Karaman, 1991 (1 species); Synphoxus Gurjanova, 1980 (1 species); Tickalerus Barnard and Drummond, 1978 (1 species); Tipimegus Barnard and Drummond, 1978 (5 species); Trichophoxus K.H. Barnard, 1930 (2 species); Uldanamia Barnard and Drummond, 1978 (1 species); Urophoxus Gurjanova, 1977 (=Pontharpinia according to Barnard and Karaman, 1991); Vasco Barnard and Drummond, 1978 (1 species); Vietophoxus Dang and Le, 2005 (1 species); Waipirophoxus Gurjanova, 1980 (1 species); Waitangi Fincham, 1977 (3 species); Wildus Barnard and Drummond, 1978 (5 species); Yammacoona Barnard and Drummond, 1978 (1 species); Yan Barnard and Drummond, 1978 (2 species).

Atlantiphoxus n. gen.

Diagnosis. Body showing deep pereonites with small coxae. Head with rostrum unconstricted; eyes absent. Antenna 1, peduncle article 2 of medium length, ventral margin with setae spread medially and distally. Antenna 2, peduncle article 4 ventral margin with long stout pectinate setae distally, facial margin with one row of setae extending to dorsal apex. Mandible molar not triturative, but as a small hump with 3 multicuspidate stout setae, incisor toothed, palpar hump small. Maxilla 1 palp 2-articulate. Maxilla 2 inner plate subequal to outer. Maxilliped palp article 4 narrow, apical nail medium. Gnathopods 1-2 anterior margin weakly setose; propodus with stout setae defining palm. Pereopods 3-4 with dactylus stout. Pereopod 5 basis broad, strongly tapering distally. Pereopod 7 basis expanded posteroventrally, anterodistal corner with a row of long plumose setae; dactylus elongate. Epimeral plate 3, posteroventral margin strongly produced and rounded. Uropod 3 outer ramus, article 2 elongate, with 2 long setae apically. Telson apex truncated, with long setae on each lobe.

Type species. Atlantiphoxus wajapi n. sp. (by monotypy)

Etymology. The genus name Atlantiphoxus is a combination of the word “Atlantic” in reference to its geographical distribution, so far exclusive to the Atlantic Ocean, plus phoxus attributed to the family name Phoxocephalidae.

Remarks. Atlantiphoxus n. gen. shares the following characters with Fuegiphoxus: antennae 1–2 flagella not reduced; right mandible molar as a hump with 3 stout multicuspidate setae, incisor with 3 teeth, palpar hump small; maxilla 1 palp 2-articulate; gnathopods 1-2 weakly setose anteriorly, without eusirid attachment, propodus ovatorectangular, palm acute; uropods 1-2 rami with apical nail immersed; telson with subtruncate apex and a weak lateral acclivity. However, the new genus differs from Fuegiphoxus by the following characteristics (characters of Fuegiphoxus in parentheses): eyes absent (present, but dubious in F. abjectus); antenna 2 article 4 stout facial setae in 1 row (up to 2 rows); pereopods 3-4 dactylus stout (slender); pereopod 7 basis with anterodistal lobe produced and bearing a row of long plumose setae (not produced, without setal row), dactylus elongate (ordinary); epimeral plate 3 strongly produced posteroventrally (not produced); uropod 1 outer ramus with 3 stout setae dorsally (1-2 setae); uropod 2 peduncle with a row of long pectinate setae (with stout and not pectinate setae); telson with 3 long setae apically on each lobe (1-2 setae).

The new genus shares the follow characters with Parharpinia as well: antenna 1 article 2 ventral setae widely spread; mandibles, palpar hump small, apex of palp oblique; maxilla 1 inner plate with 4 setae; gnathopods similar, weakly setose anteriorly, without eusirid attachment, palm acute; pereopods 3-4 carpus with posteroproximal setae; pereopods 5-6 merus and carpus narrow; uropods 1-2 rami not continuously with stout setae to apex; uropod 3 showing one ramus longer than peduncle. However, the Brazilian genus differs from Parharpinia by the following characters (characters of Parharpinia in parentheses): antenna 2 article 4 facial setal row not stout (stout setae); mandibles molar with 3 stout setae (with 4+), incisor with 4 teeth (with 3 teeth); pereopods 3-4 propodus with thin armaments (with thick armaments); pereopod 5 basis strongly tapering distally (weakly tapering); epimeral plates 1-2 with facial plumose setae and naked posteriorly (with posterior setae); epimeral plate 3 naked (with 3+ long setae); uropod 1 without apicomedial major displaced stout seta (with); telson with 3 long setae apically on each lobe (without long setae).

Atlantiphoxus n. gen. also resembles to Linca Alonso de Pina, 1993, a monotypic genus described for Argentinean waters, by the following characters: eyes absent, or at least not apparent on Linca as stated by Alonso de Pina (1993)Alonso de Pina G.M. 1993. Linca pinita, a new phoxocephalid genus and species (Crustacea: Amphipoda) from the Argentine continental shelf. Proc. Biol. Soc. Wash. 106: 497-507.; mandibles molar as a small hump with 3 stout setae, 1 being long and 2 shorter; maxilla 1 palp 2-articulate, inner plate with 4 setae; maxilliped dactyl elongate, nail medium; gnathopods small but dissimilar, carpus free, not cryptic, propodus ovate and weakly setose anteriorly; pereopod 6 basis with produced lobe posterodistally; pereopod 7 basis expanded, reaching the apex of merus, naked ventrally; epimeral plates 2-3, ventral margin with plumose setae, posterior margin naked; uropod 2 peduncle laterally combed distally. However, Atlantiphoxus n. gen. can be distinguished from Linca by the following characters (characters of Linca in parentheses): antenna 1 article 2 medium (elongate); antenna 2 article 4 facial setal row in 1 row (in 3 rows); pereopod 5 strongly tapering distally (not tapering); epimeral plate 1 posteroventral corner weakly produced into a small spine (rounded, not produced); epimeral plate 3 strongly produced and naked (not produced, with ventral and posterior setae); uropod 1 with 4 basofacial setae proximally (with 7 basofacial setae); telson with 3 long setae apically on each lobe (with 1 short and 1 medium stout setae).

The differences between Atlantiphoxus n. gen. and the closest genera are summarized in Table 1, showing the most important diagnostic characters. Although the new genus can the diagnosed by a new combination of characters, within a hypothetic clade formed by Fuegiphoxus and Parharpinia, the new taxon can be differentiated by the following exclusive features: deep pereonites with small coxae; antenna 2, article 4, stout facial setae in 1 row extending to dorsal apex; maxilliped, inner plate with 3 blunt projections apically; pereopods 3-4 with stout dactylus; pereopod 5, basis strongly tapering; pereopod 6, basis with produced posterodistal lobe; pereopod 7, basis with anterodistal lobe produced bearing a row of long plumose setae; epimeral plate 3, posteroventral corner naked, rounded and strongly produced; telson, apex truncated, with 3 long setae on each lobe apically.

Atlantiphoxus wajapi n. sp.
(Figs 1-5)

Material examined: Holotype: female, 2.6 mm, dissected and drawn, MBT 144, 23°53′S 42°28′W, 500 m depth, Rio de Janeiro state, 03 September 1970, UERJ 401. Paratypes: 1 female, dissected and drawn, MBT 180, 25°55′S 45°46′W, 224 m depth, São Paulo state, 29 May 1971, UERJ 402; 1 female, in 70% ethanol, MBT 180, 25°55′S 45°46′W, 224 m depth, São Paulo state, 29 May 1971, UERJ 403.

Diagnosis. Same as the genus.

Etymology. Named after the Wajãpi, as a tribute to the indigenous people living in the north of South America, who have been constantly and violently threatened but are resisting in an area explored by illegal miners and mining companies.

Description. Based on holotype. Habitus as in Figure 1. Head (Fig. 2A-B) with rostrum entire and unconstricted; eyes absent. Antenna 1 (Fig. 2C) peduncle article 1 about 1.9× longer than wide, ventral margin with 3 long plumose and 4 brush setae distally, dorsal margin with setules and 2 setae distally; article 2 medium, about 50% the length of article 1, ventral margin with 6 setae, facial margin with 2 setae distally; article 3 about 40% the length of article 2, ventral margin with 3 setae; primary flagellum 8-articulate; accessory flagellum 6-articulate. Antenna 2 (Fig. 2D) peduncle article 3, facial margin with 1 long seta, dorsal margin with 1 seta distally; article 4, ventral margin with 7 long stout pectinate setae, facial margin with 1 brush setae and one row of setae extending to dorsal apex, dorsal margin with 3 setae proximally; article 5, ventral margin with 8 long stout setae, dorsal margin with 2 stout setae medially; flagellum 8-articulate. Upper lip (Fig. 2G) naked, produced apically as a sub-rounded lobe. Left mandible (Fig. 2I) molar as a small hump with 3 multicuspidate stout setae, incisor with 4 teeth, lacinia mobilis elongate, with 3 teeth, 1 being minute in the middle, accessory setal row with 10 multicuspidate stout setae, palpar hump small; palp 3-articulate, article 1 short; article 2, with 3 setae; article 3 slightly longer than article 2, apex oblique, with 8 medium to long setae; Right mandible (Fig. 2J) molar as a small hump with 3 multicuspidate stout setae, incisor with 3 teeth, lacinia mobilis with 4 teeth, 1 being longer and multicuspidate, accessory setal row with 7 multicuspidate stout setae, palpar hump small; palp 3-articulate, article 1 short; article 2, with 4 setae; article 3, slightly longer than article 2, apex oblique, with 7 medium to long setae. Maxilla 1 (Fig. 2E) inner plate medial margin with 1 simple and 1 plumose seta, apical margin with setules and 2 setae; outer plate, with 11 multicuspidate stout setae; palp 2-articulate, with 9 setae apically and subapically, medial and lateral margins with setules. Maxilla 2 (Fig. 2F) inner plate slightly shorter than outer, medial margin covered with setules, subapical margin with 3 stout plumose setae, apical margin with 6 plumose setae; outer plate, lateral margin covered with setules, apical margin with simple and plumose setae. Maxilliped (Fig. 2H) inner plate medial margin with 3 setae, apical margin with 3 blunt projections and 1 stout and 3 long setae; outer plate medial margin with 5 stout and 2 long setae, apical margin with 2 long plumose and 2 stout setae, lateral margin covered with setules; palp article 2 weakly setose medially, article 3 with few setae on its margins, article 4 slender and elongate, with 1 medium apical nail.

Gnathopod 1 (Fig. 3A) weakly setose; coxa sub-rectangular, ventral margin with 10 long setae; basis about 3.4× longer than wide, anterior margin with 1 long and 1 medium setae distally, posterior margin with setae medially, posteroventral corner with 5 setae; ischium short and sub-rectangular, posteroventral corner with 3 setae; merus posterior margin with 5 setae, facial margin with 3 setae; carpus anterior margin with 2 setae, posterior margin with 12 setae, facial margin with 1 seta; propodus anterior margin with 3 setae distally, posterior margin with 1 seta medially, with 1 stout seta defining palm; palm acute, weakly sinuous, with few setae on its margin; dactylus slightly longer than palm, outer margin with 1 setule proximally and 1 spatulate seta distally. Gnathopod 2 (Fig. 3B) weakly setose; coxa sub-rectangular, ventral margin with 9 long setae; basis about 3.2× longer than wide, anterior margin with few setae, posterior margin with 5 long pectinate setae medially, posterodistal corner with a tuft of long pectinate setae; ischium small and subrectangular, posterodistal corner with 6 setae; merus posterior margin with 6 setae, facial margin with 1 seta; carpus anterior margin with 1 seta distally, posterior margin with 7 setae; propodus anterior margin with 4 setae distally, posterior margin with 1 seta medially, with 1 stout seta defining palm; palm acute, weakly sinuous, with few setae on its margin; dactylus subequal to palm, outer margin with 1 setule proximally and 1 spatulate seta distally. Pereopod 3 (Fig. 3C) coxa sub-rectangular, posterior margin weakly concave, ventral margin with 9 pectinate setae; basis about 2.8× longer than wide, posterior margin with 4 setae medially, posterodistal corner with 3 setae; ischium small and sub-rectangular, posterodistal corner with 4 setae; merus anterior margin with 5 setae distally, posterior margin moderately setose, facial margin with a row of 6 setae distally; carpus posterior margin moderately setose, with 1 thicker stout seta distally, almost reaching half of dactylus; propodus anterior margin with 1 short seta distally, posterior margin with 4 setae; dactylus stout, about 75% the length of propodus. Pereopod 4 (Fig. 3D) coxa weakly expanded anteriorly, posterodorsal margin excavate, ventral margin with 17 pectinate setae; basis about 2.9× longer than wide, posterior margin and posterodistal corner with 4 setae each; ischium small and sub-rectangular, posterodistal corner with 3 setae; merus anterior margin with 5 setae distally, posterior margin moderately setose; carpus posterior margin moderately setose, with 1 thicker stout seta distally, almost reaching half of dactylus; propodus anterior margin with 1 short seta distally, posterior margin with 4 long setae; dactylus stout, about 75% the length of propodus. Pereopod 5 (Fig. 4A) coxa bilobate, posteroventral margin weakly expanded, with 1 short seta; basis about 1.4× longer than wide, strongly tapering distally, anterior margin with 2 setae proximally and 5 distally, posterior margin with 1 seta medially; ischium small and sub-rectangular, facial margin with row of 5 setae extending to anterodistal corner; merus anterior margin moderately setose, with a row of 5 setae distally, posterior margin with 5 papposerrate and 5 stout setae; carpus facial setal formula: 3-5-4-3, anterior margin with 8 long setae, posterior margin with papposerrate and simple setae; propodus anterior and posterior margins weakly setose, distal apex with 9 setae; dactylus elongate, about 70% the length of propodus. Pereopod 6 (Fig. 4B) coxa sub-rounded, posteroventral margin weakly expanded, with 2 setae; basis about 1.2× longer than wide, anterior margin with long plumose and stout setae medially, anterodistal corner with a row of 8 long plumose setae, posterior margin with setules; ischium small and subquadrate, anterior margin with 4 plumose setae; merus anterior margin with 4 stout and 4 long setae, posterior margin with 3 stout and 8 long setae; carpus facial setal formula: 3-5-3-6, posterior margin with 1 stout and 5 long setae; propodus anterior margin with 1 long and 2 stout setae, posterior margin with 1 stout and 3 long setae, distal apex with 1 stout and 6 setae; dactylus elongate, about 70% the length of propodus. Pereopod 7 (Fig. 4C) coxa sub-rounded, posteroventral margin with 1 short seta; basis slightly wider than long, expanded posteroventrally, almost reaching the apex of merus, anterior margin with 5 setae proximally, anterodistal lobe produced with a row of 16 long plumose setae, posterior margin with 6 serrations, with setules and 1 long seta, ventral margin smooth; ischium small and sub-rectangular, distal lobe produced, anterior margin with 5 plumose setae, posterior margin with setules; merus anterior margin with 6 setae, posterior margin with 1 seta distally; carpus anterior and posterior margins weakly setose; propodus anterior margin with 6 setae, posterior margin with 7 setae; dactylus elongate, about 80% the length of propodus, outer margin with 1 short plumose seta proximally.

Epimeral plate 1 (Fig. 5A) anterior and ventral margins almost straight, with facial row of long plumose setae, anteroventral corner rounded, posteroventral corner weakly produced into a small spine, posterior margin convex. Epimeral plate 2 (Fig. 5B) anterior and ventral margins almost straight, with facial row of 5 long plumose setae, anteroventral and posteroventral corners rounded, posterior margin convex. Epimeral plate 3 (Fig. 5C) anterior margin weakly concave, anteroventral corner rounded, ventral margin weakly concave proximally, posteroventral corner rounded and strongly produced. Uropod 1 (Fig. 5D) peduncle 2.9× longer than wide, with 4 basofacial setae proximally, dorsolateral corner with 1 stout setae, dorsomedial margin with 5 setae; outer ramus dorsal margin with 3 stout setae, bearing 1 apical nail; inner ramus subequal to outer, dorsal margin with 1 stout seta, bearing apical nail. Uropod 2 (Fig. 5E) peduncle 2× longer than wide, dorsolateral corner weakly projected and laterally combed distally, dorsomedial margin with 8 long stout pectinate setae; outer ramus dorsal margin with 3 stout setae, bearing 1 apical nail; inner ramus subequal to outer, naked, bearing 1 apical nail. Uropod 3 (Fig. 5F) peduncle 1.5× longer than wide, ventral margin with 5 long setae distally, dorsal margin with 1 short seta; outer ramus about 1.9× longer than inner, article 1 ventral margin with 4 setae medially and 3 distally, dorsal margin with 1 long seta distally, article 2 elongate, with 2 long pectinate setae apically; inner ramus with 2 setae apically. Telson (Fig. 5G) about 85% cleft, apex truncate, with 3 long setae and 1 short seta on each lobe, dorsal margin with 2 short plumose setae medially.

Type locality. Rio de Janeiro state coast (23°53’S 42°28’W).

Ecological data. Atlantiphoxus wajapi n. gen., n. sp. was collected with a rectangular dredge on a sediment bottom covered with Globigerina ooze and dark grey mud (station MBT 144). There is no sediment information for station MBT 180.

Geographic distribution: The species is known for the coast of the Brazilian states of Rio de Janeiro (23°53’S 42°28’W) and São Paulo (25°55’S 45°46’W) (Fig. 6).

DISCUSSIONTop

Atlantiphoxus wajapi n. sp. has the following new combination of noteworthy characters: Body with deep pereonites and small coxae. Head with rostrum unconstricted; eyes absent; maxilliped, inner plate apical margin with 3 blunt projections and 1 stout seta apically; palp apical nail medium. Gnathopods 1–2 propodus with 1 stout seta defining palm; palm weakly sinuous; dactylus outer margin with 1 spatulate seta distally. Pereopods 3–4 carpus ventral margin with main stout distal setae exceeding the apex of propodus. Pereopod 5 basis proximally broad and strongly tapering distally. Pereopod 6 posterodistal lobe produced, anterodistal margin with a row of long plumose setae extending to facial margin. Pereopod 7 basis expanded posteroventrally, almost reaching the apex of merus, posterior margin serrate, anterodistal lobe produced and with a row of long plumose setae; dactylus elongate. Epimeral plates 1–2 facial margin with long plumose setae. Epimeral plate 3 naked, posteroventral margin strongly produced and rounded. Uropods 1–2 rami not continuously with stout setae to apex, bearing apical nail. Uropod 2 peduncle dorsal margin with a row of long pectinate setae. Telson apex truncated, with 1 short plumose and 3 long setae on each lobe, dorsal margin with 2 plumose setae.

Considering the statements by Barnard and Drummond (1978)Barnard J.L., Drummond M.M. 1978. Gammaridean Amphipoda of Australia, part III: The Phoxocephalidae. Smith. Contrib. Zool. 245: 1-551., the ancestor of the phoxocephalids would have an enlarged second gnathopod. Thus, the new genus can be hypothesized as more advanced and derived from Fuegiphoxus based on the reduction in size of gnathopod 2 and the elongation of its propodus. It was assumed by the same authors that the phoxocephalids used the Magellanic region, which has 17 phoxocephalid species grouped into 11 genera (Alonso de Pina et al. 2008Alonso de Pina G.M., Rauschert M., De Broyer C. 2008. A catalogue of the Antarctic and sub-Antarctic Phoxocephalidae (Crustacea: Amphipoda: Gammaridea) with taxonomic, distribution and ecological data. Zootaxa 1752: 1-40.), as a main stopover during the migratory processes from Australia. The Australian waters are considered a main centre of origin for Phoxocephalidae, since it retains Pontharpinia, treated as the most primitive genus within the family (Barnard and Karaman 1983Barnard J.L., Karaman G.S. 1983. Australia as a major evolutionary centre for Amphipoda (Crustacea). Mem. Aus. Mus. 18: 45-61.). These centres are taken as hotspots where successful taxa are able to leave and spread around prosperous regions (Briggs 2003Briggs J.C. 2003. Marine centres of origin as evolutionary engines. J. Biogeogr. 30: 1-18.). Barnard and Drummond (1978)Barnard J.L., Drummond M.M. 1978. Gammaridean Amphipoda of Australia, part III: The Phoxocephalidae. Smith. Contrib. Zool. 245: 1-551. proposed a theory for the migration process of the subfamily Harpiniinae, and this hypothesis can be extended to the Phoxocephalinae as well, assuming that the new genus is an outcome of the migratory phoxocephalid pathway towards northern waters through the deep sea, since Fuegiphoxus is currently recorded for the western Antarctic, sub-Antarctic and Magellan region at depths of 0 to 1031 m (Alonso de Pina et al. 2008Alonso de Pina G.M., Rauschert M., De Broyer C. 2008. A catalogue of the Antarctic and sub-Antarctic Phoxocephalidae (Crustacea: Amphipoda: Gammaridea) with taxonomic, distribution and ecological data. Zootaxa 1752: 1-40., Chiesa and Alonso 2011Chiesa I.L., Alonso G.M. 2011. Redescription and generic assignment of Fuegiphoxus uncinatus (Chevreux, 1912) (Crustacea, Amphipoda, Phoxocephalidae). Zoosystema 33: 219-233.). This explanation agrees with the statement by Myers and Lowry (2009)Myers A.A., Lowry J.K. 2009. The biogeography of Indo-West Pacific tropical amphipods with particular reference to Australia. In: Lowry J.K., Myers A.A., (eds). Benthic Amphipoda (Crustacea: Peracarida) of the Great Barrier Reef, Magnolia Press, Australia. Auckland, pp. 109-127. regarding the Trans-Pacific tracks of other benthic amphipods of the superfamily Haustorioidea, such as Phoxocephalopsidae Barnard and Drummond, 1982, Urohaustoriidae Barnard and Drummond, 1982 and Zobrachoidae Barnard and Drummond, 1982.

ACKNOWLEDGEMENTSTop

The authors are grateful to Dr Maria Teresa Valério-Berardo (IO-USP) for donation of the material examined. This work is part of the PhD thesis of L.F.A. in the post-graduate programme in Animal Biology, Universidade Federal Rural do Rio de Janeiro (PPGBA-UFRRJ). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. A.R.S. thanks the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for providing a grant, process number E-26/202.768/2019.

REFERENCESTop

Alonso de Pina G.M. 1993. Linca pinita, a new phoxocephalid genus and species (Crustacea: Amphipoda) from the Argentine continental shelf. Proc. Biol. Soc. Wash. 106: 497-507.

Alonso de Pina G.M., Rauschert M., De Broyer C. 2008. A catalogue of the Antarctic and sub-Antarctic Phoxocephalidae (Crustacea: Amphipoda: Gammaridea) with taxonomic, distribution and ecological data. Zootaxa 1752: 1-40.
https://doi.org/10.11646/zootaxa.1752.1.1

Alonso G.M., Chiesa I.L. 2014. Phoxocephalidae. In: Roig-Juñent S., Claps L.E., Morrone J.J. (eds), Biodiversidad de Artropodos Argentinos - Vol. 3. INSUE-UNT, San Tucuman, Argentina, pp. 205-213.

Andrade L.F., Senna A.R. 2019a. Two new species of Cephalophoxoides Gurjanova, 1977 (Crustacea: Amphipoda: Phoxocephalidae) from southeastern Brazil, with comments on the taxonomic status of the genus. Zootaxa 4712: 531-551.
https://doi.org/10.11646/zootaxa.4712.4.3

Andrade L.F., Senna A.R. 2019b. First record of the genus Limnoporeia Fearn-Wannan, 1968 (Crustacea: Amphipoda: Phoxocephalidae) from the Atlantic Ocean, with description of a new species. J. Nat. Hist. 53: 2517-2531.
https://doi.org/10.1080/00222933.2019.1705931

Andrade L.F., Senna A.R. 2020. A novel species of Heterophoxus Shoemaker, 1925 (Crustacea, Amphipoda, Phoxocephalidae) from southeast and southern Brazil, with an identification key to world species of the genus. Eur. J. Taxon. 592: 1-16.
https://doi.org/10.5852/ejt.2020.592

Arfianti T., Wilson S., Costello M.J. 2018. Progress in the discovery of amphipod crustaceans. PeerJ 6: e5187.
https://doi.org/10.7717/peerj.5187

Barnard J.L., Drummond M.M. 1976. Classification of five genera of Phoxocephalidae (Marine Amphipoda). Proc. Biol. Soc. Wash. 88: 515-548.

Barnard J.L., Drummond M.M. 1978. Gammaridean Amphipoda of Australia, part III: The Phoxocephalidae. Smith. Contrib. Zool. 245: 1-551.
https://doi.org/10.5479/si.00810282.245

Barnard J.L., Drummond M.M. 1982. Gammaridean Amphipoda of Australia, Part V: Superfamily Haustorioidea. Smith. Contrib. Zool. 360: 1-148.
https://doi.org/10.5479/si.00810282.360

Barnard J.L., Karaman G.S. 1983. Australia as a major evolutionary centre for Amphipoda (Crustacea). Mem. Aus. Mus. 18: 45-61.
https://doi.org/10.3853/j.0067-1967.18.1984.371

Barnard J.L., Karaman G. 1991. The families and genera of marine gammaridean Amphipoda (except marine Gammaroidea). Part 2. Rec. Aust. Mus. 13: 419-866.
https://doi.org/10.3853/j.0812-7387.13.1991.367

Briggs J.C. 2003. Marine centres of origin as evolutionary engines. J. Biogeogr. 30: 1-18.
https://doi.org/10.1046/j.1365-2699.2003.00810.x

Chiesa I.L., Alonso G.M. 2011. Redescription and generic assignment of Fuegiphoxus uncinatus (Chevreux, 1912) (Crustacea, Amphipoda, Phoxocephalidae). Zoosystema 33: 219-233.
https://doi.org/10.5252/z2011n2a5

De Broyer C., Lowry J.K., Jazdzewski K., et al. 2007. Census of Antarctic Marine Life. Synopsis of the Amphipoda of the Southern Ocean. Part. 1. Catalogue of the Gammaridean and Corophiidean Amphipoda (Crustacea) of the Southern Ocean with distribution and ecological data. Bull. Inst. R. Sci. Nat. Belg. 77: 1-325.

Garm A., Watling L. 2013. The crustacean integument: setae, setules, and other ornamentation. In: Watling T., Thiel M., (eds). The Natural History of the Crustacea. Functional Morphology and Diversity. Oxford Univ. Press, Oxford, pp. 167-198.
https://doi.org/10.1093/acprof:osobl/9780195398038.003.0006

Gurjanova E.F. 1977. Some new data in taxonomy of family Phoxocephalidae sensu lato (Amphipoda, Gammaridea). Report I. Proc USSR Acad Sci. 21: 67-87.

Hartman O. 1955. Quantitative survey of the benthos of San Pedro Basin, Southern California. Part I. Preliminary results. Allan Hancock Pac Exped. 19: 1-185.

Horton T., Lowry J.K., De Broyer C., et al. 2019. World Amphipoda Database. Phoxocephalidae G.O. Sars, 1891. Accessed through: World Register of Marine Species on 26/9/2019 at:
http://www.marinespecies.org/aphia.php?p=taxdetails&id=101403

Jarret N.E., Bousfield E.L. 1994a. The amphipod superfamily Phoxocephaloidea on the pacific coast of North America. Family Phoxocephalidae. Part I. Metharpiniinae, new subfamily. Amphipacifica 1: 58-140.

Jarret N.E., Bousfield E.L. 1994b. The amphipod superfamily Phoxocephaloidea on the pacific coast of North America. Family Phoxocephalidae. Part II. Subfamilies Pontharpiniinae, Paharpiniinae, Brolginae, Phoxocephalinae, and Harpiniinae. Systematics and distributional ecology. Amphipacifica 3: 71-150.

Lowry J.K., Myers A.A. 2017. A Phylogeny and Classification of the Amphipoda with the establishment of the new order Ingolfiellida (Crustacea: Peracarida). Zootaxa 4265: 1-89.
https://doi.org/10.11646/zootaxa.4265.1.1

Myers A.A., Lowry J.K. 2009. The biogeography of Indo-West Pacific tropical amphipods with particular reference to Australia. In: Lowry J.K., Myers A.A., (eds). Benthic Amphipoda (Crustacea: Peracarida) of the Great Barrier Reef, Magnolia Press, Australia. Auckland, pp. 109-127.
https://doi.org/10.11646/zootaxa.2260.1.4

Poore A.G.B., Lowry J.K. 1997. New ampithoid amphipods from Port Jackson, New South Wales, Australia (Crustacea: Amphipoda: Ampithoidae). Invertebr. Taxon. 11: 897-941.
https://doi.org/10.1071/IT95045

Senna A.R. 2010. A new genus and five new species of Phoxocephalidae (Crustacea: Amphipoda) from the south-east Brazilian deep sea. J. Nat. Hist. 44: 2075-2118.
https://doi.org/10.1080/00222933.2010.486081

Senna A.R., Souza-Filho J.F. 2011. A new species of Pseudharpinia (Amphipoda: Haustorioidea: Phoxocephalidae) from Southeastern Brazilian continental shelf. Nauplius 19: 7-16.
https://doi.org/10.1590/S0104-64972011000100002

Taylor J. 2006. A new species of Leongathus from the Tasman Sea collected during the 2003 NORFANZ Expedition (Crustacea: Amphipoda: Phoxocephalidae). Mem. Mus. Vic. 63: 207-213.
https://doi.org/10.24199/j.mmv.2006.63.16

Taylor J., Poore G.C.B. 2001. Descriptions of new species of Birubius (Amphipoda: Phoxocephalidae) from Australia and Papua New Guinea with comments on the Birubius-Kulgaphoxus-Tickalerus-Yan complex. Mem. Mus. Vic. 58: 255-295.
https://doi.org/10.24199/j.mmv.2001.58.15