Emerita almeidai Mantelatto & Balbino, 2023

Mantelatto, Fernando L., Paixao, Juliana M., Robles, Rafael, Teles, Jeniffer N. & Balbino, Felipe C., 2023, Evidence using morphology, molecules, and biogeography clarifies the taxonomic status of mole crabs of the genus Emerita Scopoli, 1777 (Anomura, Hippidae) and reveals a new species from the western Atlantic, ZooKeys 1161, pp. 169-202 : 169

Emerita almeidai Mantelatto & Balbino sp. nov.

Figs 1 , 5 , 6 , 8 , 9 , 10 , 11 , 12

Emerita portoricensis - Efford, 1976: 178, 179; Calado 1990: 266, 268, 271; Tam et al. 1996: 490; Haye et al. 2002: 904 (non Emerita portoricensis Schmitt, 1935).

Type material.

Holotype: ovigerous ♀ (cl. 13.52 mm), CCDB 7233, Praia do Paiva (lower intertidal, quartzite, coarse sand off wave-washed beach), Ilha do Amor, Cabo de Santo Agostinho, PE, Brazil, 08°13'48"S, 34°55'22"W, 27 August 2022, colls. Mantelatto, F.L., Bochini, G.L., Balbino, F.C., Rios, A. Paratypes: 3 ovigerous ♀s (cl. 17.31 mm, 17.93 mm, 15.90 mm), 1 ♀ (cl. 14.67mm) (1 ovigerous ♀ cl. 17.31 mm dissected - left antennule, antennae, mouthparts, maxillipeds, pereopods, uropods and telson), CCDB 5855, Praia de Serrambi, Município de Serrambi, Ipojuca, PE, Brazil, 08°33'39.91"S, 35°00'45.15"W, 20 July 2015, colls. Mantelatto, F.L., Mantelatto, F.B., Biagi, R.; 3 ovigerous ♀s (cl. 15.01 mm, 15.93 mm, 9.94 mm), 4 ♀s (cl. 9.66 mm, 9.64 mm, 9.24 mm, 9.02 mm), 1 juvenile (cl. 4.72 mm), "1 ovigerous ♀ (cl. 15.01 mm dissected - mouthparts, maxillipeds, pereopods, uropods and telson), CCDB 4937, Praia de Boa Viagem, Recife, PE, Brazil, 08°08'12.96"S, 34°54'05.84"W, 28 January 2014, colls. Mantelatto, F.L., Mantelatto, F.B., Biagi, R.; 1 ♀ (cl. 10.49 mm), MOUFPE 20112, Praia do Paiva, Ilha do Amor, Cabo de Santo Agostinho, PE, Brazil, 08°13'48"S, 34°55'22"W, 27 August 2022, colls. Mantelatto, F.L., Bochini, G.L., Balbino, F.C., Rios, A.; 1 ♂ (cl. 7.29 mm), MZUSP 43536, Praia do Forte Orange, Vila Velha, Ilha de Itamaracá, PE, Brazil, 07°50'40"S, 34°50'33"W, 30 August 2022, colls. Mantelatto, F.L., Bochini, G.L., Balbino, F.C., Rios, A., Almeida, A.O."

Additional material.

1 ♀, CCDB 4526, Morro Branco (CE), 25 March 1989 ; 1 ♀, 1 ovigerous ♀, CCDB 3369, Praia de Perobas , Touros (RN), 10 June 2011 , colls. Robles , R., Pileggi, L.G.; 5 ovigerous ♀ s, CCDB 3376, Praia de Maracajau , Maxaranguape (RN), 10 June 2011 , colls. Robles , R., Pileggi, L.G .; 2 ♀ s, 1 ovigerous ♀, CCDB 3393, Morro do Careca , Ponta Negra, Natal (RN), 06 June 2011, coll. Robles, R. ; 1 ♀, 4 ovigerous ♀ s, CCDB 3380, Morro do Careca , Ponta Negra, Natal (RN), 07 June 2011, coll. Robles, R. ; 2 ♀ s, 10 ovigerous ♀ s, CCDB 4869, Praia de Maragogi , Maragogi (AL), 05 October 2013 , colls. Mantelatto, F.L., Mantelatto F.B.; 2 ♀ s, 2 ovigerous ♀ s, CCDB 6127, Praia de Imbassai , Mata de São João (BA), 25 January 2017 , colls. Mantelatto, F.L., Mantelatto, F.B.; 1 ovigerous ♀, CCDB 2606, Praia do Pe da Serra , Uruçuca (BA), 31 March 2009 , colls. Mantelatto, F.L., Almeida, A.O.; 1 ovigerous ♀, CCDB 2605, Praia do Sul , Km 01, Hotel Praia do Sol, Ilhéus (BA), 30 March 2009 , colls. Mantelatto, F.L., Almeida, A.O.; 2 ovigerous ♀ s, CCDB 3026, Praia do Sul , Km 01, Hotel Praia do Sol, Ilhéus (BA), 10 November 2010 , colls. Mantelatto, F.L., Peiró, D.F.; 1 ♀, 1 ♂, CCDB 4262, Praia da Lagoa Pequena , Prado (BA), 12 August 2012 , colls. Carvalho, F.L., Souza-Carvalho, E.A.; 1 ♂, 3 ♀ s, 1 ovigerous ♀, CCDB 3992, Praia de Iriri , Iriri (ES), 19 June 2012 , colls. Carvalho, F.L., Robles , R., Peiró, D.F.; 2 ovigerous ♀ s, CCDB 4376, Pedra do Sal (RJ), 19 November 2009, coll. Arresda, E.

Comparative material.

Emerita analoga : 4 ovigerous ♀ s, CCDB 4870, Calfuco , XIV Región, Chile, 20 August 2013, coll. Fuentes, J.P. ; Emerita benedicti : 5 ♀ s, 4 juveniles, CCDB 4674, Playa Escondida , Los Tuxtlas, México, 07 February 2013, coll. Robles, R. ; Emerita brasiliensis : 7 ♀ s, 6 ♂ s, CCDB 3990, Laguna Marginal , Guarapari (ES), Brazil, 18 June 2012 , colls. Carvalho, F.L., Robles, R., Peiró, D.; 7 ♂ s, 12 ♀ s, 1 ovigerous ♀, 5 juveniles, CCDB 7226, Praia de Iriri , Anchieta (ES), Brazil, 19 June 2012 , colls. Carvalho, F.L., Peiró, D., Robles, R.; 3 ♀ s, CCDB 1030, Ubatuba (SP), Brazil, 20 November 2002 , colls. Mantelatto, F.L., Scelzo, M.A.; 1 ♀, 1 ovigerous ♀, CCDB 2552, Praia Juquehy , São Sebastião (SP), Brazil, 26 December 2008 , colls. Mantelatto, F.L., Mantelatto, F.B., Biagi, R.; 1 ♀, CCDB 7301, Praia de Guaratuba , Bertioga (SP), Brazil, 07 January 2023 , colls. Mantelatto, F.L., Mantelatto, F.B., Mantelatto, H.B.; 2 ♂ s, 6 ♀ s, 2 ovigerous ♀ s, CCDB 3924, Praia Guaiuba , Guarujá (SP), 22 October 2011 , colls. Rossi, N.; Leone, I., Carvalho, F.L., Costa, A.; 5 ♀ s, CCDB 1443, Praia Itarare , São Vicente (SP), Brazil, 23 October 2011 , colls. Rossi, N., Leone, I., Carvalho, F.L., Costa, A.; 3 ♂ s, 1 ♀, 7 ovigerous ♀ s, CCDB 4409, Praia de Balneario Camboriu , Camboriú (SC), Brazil, 04 December 2012 , colls. Carvalho, F.L., Souza-Carvalho, E.A.; Emerita portoricensis : ovigerous ♀ (holotype, USNM 65731, photos), Mayaguez, Puerto Rico, 19-20 January 1899 ; 3 ♀ s, CCDB 3525, Playa Boca Del Drago , Bocas Del Toro, Panamá, 06 August 2011 , colls. Mantelatto, F.L., Negri, M.P., Rossi, N., Magalhães, T.; Emerita rathbunae : 3 ♀ s, CCDB 1029, Playa Del Revolcadero , Granjas Del Marquez, Acapulco, México, 06 May 2012, coll. Mantelatto, F.L. ; Emerita talpoida : 9 ♀ s, CCDB 4675, Playa Escondida , Los Tuxtlas, México, 07 February 2013, coll. Robles, R.

Diagnosis.

Carapace dorsally convex, 1.42-1.54 × longer than wide, surface densely covered by microcrenulate rugae; most rugae elongate and continuous across carapace median line not forming rows or lines; 17 or more rugae crossing median line, rugae obsolete laterally on epimeral lobes. Front with three distinct subacute lobes consisting of rostrum and two lateral projections, rostrum visibly shorter than lateral projections. Antennular flagellum dorsal ramus with 30 articles. Antennal peduncle second article large, with three distal spines, median spine the longest, antennal flagellum with 74-104 articles. First maxilla proximal endite rounded, subcircular with margins visibly convex; endopodal palp wide, short, distal end upturned. Third maxilliped without exopod, endopod with merus distal inner margin projected into strong subtriangular lobe, lateral margins of merus sinuous, outer distal margin ending on acute angle. First pereopod merus large, inflated, broad truncate lobe on inferior margin of merus, carpus distal end with large spine, propodus ca. as long as dactylus; dactylus elongate, more than twice as long as wide, superior surface almost straight, inferior surface convex with low, moderate, and regularly spaced serrations, dactylus lined by long plumose setae and short spiniform setae or spinules, terminus of dactylus with single short spine, terminus subacute. Pleon with second pleonite larger than others, tergite as wide as carapace, sides of second pleonite forming wide flanges laterally, second and third pleonite with two pairs of rugae extending from junction with next pleonite almost to ventrolateral margin. Overall coloration olive grey, white laterally, rugae distinctly white in coloration, few thin white bars or stripes near posterolateral regions of carapace.

Description.

Carapace (Figs 1A , 5D , 6B , 8A , 11 , 12A ) elongate, 1.42-1.54 × longer than wide, subcylindrical, overall dorsally convex, highly convex transversely, slightly convex longitudinally; carapace surface densely covered by low transverse microcrenulate to microdenticulate rugae, many of which are continuously elongate, not forming proper lines or rows of rugae, many continuous across middorsal region on anterior and posterior portions of carapace, usually 17 or more rugae extending across postcervical middorsal line; pterygostomial region with ventrolateral rugae; rugae separating small, anteriorly curved ridges; anterior margin of broad epimeral lobe of carapace with serrated appearance due to presence of such ridges. Pterygostomial plates densely punctate, separated from carapace by post-gastric groove; low slightly rugose ridge extending from median portion almost to distal end of plate, parallel to carapace margin for most of its extension, slightly deflected inwards near distal end. Front (Figs 5D , 6F ) with three subacute dentiform projections; median projection forming broad triangular or subtriangular rostrum surrounded by relatively long plumose setae, distal end of rostrum sharply pointed, rostrum visibly shorter than lateral projections; lateral projections subtriangular with concave sides proximally and straight sides distally, visibly longer than rostrum, also surrounded by relatively long plumose setae; rostrum and lateral projections separated by wide U-shaped sulcus. Anterolateral margins of carapace just to the side of frontal projections surrounded by short plumose setae. Transverse frontal groove parallel to front, mostly straight, slightly bent at lateral extremes. Cervical groove just anterior to midlength of carapace, crescent shaped with convex face facing posteriorly, slight anteriorly facing notch on cervical groove on carapace midline. Most rugae broken, obsolete or absent on lower broad epimeral lobe.

Eyes (Fig. 5D ) swollen at end of very narrow and elongated peduncles, reaching anteriorly past distal portion of fifth antennal peduncle article when extended and past spines of second antennal article when retracted; ocular peduncles composed of three articles; first article arcuate, longer than wide, convex on internal face and concave on external face; second article deflected downwards, longer than first article; third article long, first third wider, other two thirds very narrow, widening near eye.

Antennules (Fig. 8C ) short; antennular peduncle composed of three articles; first article wider than others, external surface with large dentiform projection near base of article; second article densely setose, trapezoid in shape, dorsal surface shorter, ventral surface longer; third article short, also trapezoid in shape, dorsal surface longer, ventral surface shorter; flagellum dorsal ramus longer, with 30 articles, ventral ramus shorter, with 12 articles.

Antenna (Figs 6J , 8D ) long; antennal peduncle composed of five articles; first article trapezoidal, longer than wide; second article large, covered by sparse rugae, distal end with three large spiniform projections, median projection longest, dorsal and ventral projections ca. the same size as each other, sulcus extending across dorsolateral surface from proximal end to base of dorsal spiniform projection, microdenticulate ridge separating ventral projection from median projection, one row of setose rugae present on mesial ventral portion; third article inserted on lateral portion of second article, completely concealed by second article in lateral view, trapezoidal in shape, proximal portion rectangular in shape, distal portion triangular, short line of setae parallel to distal margin; fourth article dorsally convex, ventrally Y-shaped; fifth article elongate, slimmer near base, inflated distally, row of setae on ventral margin; flagellum long, composed of 74-104 articles with dense long setae ventrally in adult specimens, number of articles smaller in juveniles, first article longest, ~ 3 × as long as other articles.

Mandible (Fig. 9A ) membranous, mostly fused with posterior margin of epistome; gnathal lobe short, kidney-shaped, inserted basally on mandible, projected inwards, external margin convex, internal margin concave, long plumose setae along mesial and distal margins; palpus composed of two articles, longer than gnathal lobe; first article subrectangular; terminal article suboval, lined by many long setae.

First maxilla (Fig. 9B ) small; proximal endite loosely connected to rest of appendage, oval, flattened, lateral and distal margins surrounded by relatively long setae; distal endite elongate, narrow, distal end slightly wider, pin-shaped, margins lined by setae, setae on proximal internal side very long, median and distal setae shorter, setae on proximal and median external portions shorter, longer subdistally; endopodal palp nearly as wide as long, tip slightly hooked upwards.

Second maxilla (Fig. 9C ) exopod developed as scaphognathite attached to base, proximal and distal lobes flattened, lined by long setae, proximal lobe semi-oval in shape, broader, distal lobe semi-oval, slimmer; endopod short, wider proximally, narrowed towards distal end, subacute tip deflected distally.

First maxilliped (Fig. 9D ) membranous; exopod larger, arched, composed of two articles; proximal article subrectangular, outer margin convex, inner margin concave, distal article subovoid, surrounded distally by many long plumose setae, outer margin proximally convex until ca. midpoint, where it becomes concave, inner margin convex throughout its extension; endopod minute, elongate, membranous, with small tuft of setae subterminally; distal endite crescent shaped, exceeding length of exopod first article, extensively covered by short setae on external surface, inner margin covered by dense long plumose setae, patch of relatively long plumose setae present on distal end.

Second maxilliped (Fig. 9E ) membranous, exopod and endopod subequal; exopod composed of two articles; proximal article elongate, subtriangular, widest proximally, narrowing towards distal end, sparsely setose; distal article subovoid, margins surrounded by long plumose setae; endopod composed of four articles; ischio-merus narrow, arcuate in shape, proximal end wider, narrowing towards distal end, outer margin convex lined by several long setae, inner margin concave lined by several setae; carpus short, inflated, distal and lateral margins densely covered by long plumose setae; propodus short, less robust than carpus, margins covered by setae; dactylus long, narrow, elongate, widest at base, narrowing towards distal rounded end, ~ 2/3 as long as ischio-merus, surrounded by long setae.

Third maxilliped (Fig. 9F, G ) lacking exopod; endopod with coxa wider than long, small subtriangular projection on proximal inner side, base-ischium minute, much wider than long, merus broad, sparse setose rugae present on outer face, inner face mostly smooth with one large and distinct ridge crossing merus from base-ischium junction to carpus junction, margins lined by short setae, long plumose setae distally, nearly twice as long as wide, proximal third of inner margin very rounded, convex, distal two thirds straight, large subtriangular projection on distal end of inner portion of merus overlying part of carpus and propodus, outer margin slightly concave proximally, convex distally, distal end of outer portion of merus straight, carpus short, subquadrate, distal margin and inner face covered by long setae, propodus long, slightly curved inwards, outer face smooth, inner face densely covered in setae, dactylus long, shorter than propodus, slightly curved inwards, distal end rounded, outer face smooth inner face densely covered in setae.

First pereopod (Fig. 10A ) coxa subtrapezoidal, sparsely covered by setose rugae on external face, setae on ventral margin and distal end, ventral dentiform projection proximally; base-ischium longer than wide, minute, lined by setae ventrally, with two lobes separated by median notch, ventral margin surrounded by setae; merus large, subcircular, sparsely covered by setose rugae, superior margin convex, inferior margin convex proximally, extended laterally forming truncate lobe with straight or almost straight lateral margin, small short sulcus on mesial portion of distal end of merus; carpus elongate, crossed by some oblique rows of setose rugae on distal ventral portion, three very distinct small perpendicular rows of setose rugae on dorsal surface separating article from large narrow distal spine, spine reaching to base of dactylus; propodus subtrapezoidal in shape, sparsely surrounded by setae, sparse setose rugae present, a transversal ridge running along most of ventrolateral portion of propodus, including distal process (Fig. 8B ), dense short setae running along ridge, distal process long, subtriangular, strong oblique ridge running from dactylus junction to base of distal process, superolateral surface of distal process excavate, fits base of dactylus, long setae present on distal process; dactylus (Figs 5D , 6D , 8B ) elongate, usually more than twice as long as wide, superior margin mostly straight, inferior surface convex, inferior surface moderately serrated from median portion to distal end, terminus of dactylus acute or subacute bearing one small spine, weakly arched oblique ridge across superior portion of dactylus, ridge originating near median portion of junction with propodus, running upwards towards superior margin, fusing with superior margin around median portion of dactylus, ridge lined by small setae, long plumose setae surrounding dactylus, small spiniform setae among them.

Second through fourth pereopods (Fig. 10B, C, D ) similar in configuration. Second pereopod coxa subquadrate; base-ischium small, longer than wide, surrounded by setae; merus large, subrectangular, longer than wide, surface covered by sparse setose rugae, superior margin mostly straight, convex towards distal end, inferior margin slightly concave, large dentiform projection protruding ventrally from distal end of merus, inferior margin lined by setae; carpus subtriangular, external surface with two short ridges present, one on superior and one on inferior regions of article, internal surface setose, crossed mesially by single row of setae, inferior portion with small triangular projection distally lined by setae; propodus wider than long, subrectangular, superior margin oblique, external face with small triangular projection positioned distally on dorsal region overlying part of dactylus, transverse ridge near superior margin, internal face with large spiniform projection lined by large setae at ca. same position; dactylus large, flattened, hook-shaped, broad proximally, narrowing distally, superior margin concave, inferior margin convex, distal tip upturned, inferior margin surrounded by long setae. Third pereopod coxa and base-ischium similar to second pereopod; merus subrectangular, much longer than wide; carpus very large, subtriangular, superior and inferior ridges present, propodus wider than long, subrectangular, superior margin oblique, small ridge near superior margin present, small triangular projection positioned distally on superior margin overlying part of dactylus; dactylus large, hook-shaped, flattened, broad proximally, narrowing distally, superior margin concave, inferior margin convex, distal tip upturned, inferior margin surrounded by setae. Fourth pereopod coxa and base-ischium similar to that of second and third pereopods; merus elongate, much longer than wide, subrectangular; carpus large, longer than wide, inferior surface almost straight, superior surface convex; propodus subquadrate, nearly as wide as long, lacking triangular projection, line of short setae near superior margin; dactylus large, somewhat flattened, broad distally, narrowing towards distal end, proportionally smaller than in other pereopods, subtriangular, superior and inferior margins almost straight, tip not upturned, a line of short setae parallel to superior margin, inferior margin lined by setae.

Fifth pereopod (Fig. 10E ) reduced, concealed under carapace; all articles except for dactylus elongate, much longer than wide, with small tufts of setae distally; propodus long, with distal projection that along with dactylus forms a small chela; dactylus short, deflected inwards; chela small, covered by setae.

Pleon short, partly recurved under carapace. First pleonite smallest, minute, much wider than long, fitting into posterior concavity of carapace; second pleonite larger than others, as wide as carapace, median portion of pleonite narrow, both sides of pleonite enlarged, forming two wide lateral flanges, flanges with pair of long transverse rugae extending from third pleonite junction almost to ventrolateral margins of tergite, distal portion of ventrolateral region of each pleonite with short transverse ruga extending from superior margin to inferior margin of narrowest portion of flange, wide lateral flanges forming space where third pleonite fits; third pleonite smaller than second, sides of pleonite somewhat enlarged forming flanges that are mostly covered by flanges of second pleonite, two transverse rugae extending from junction with fourth pleonite to junction with second on each flange; fourth pleonite smaller than third, sides slightly enlarged forming flanges which are mostly covered by flanges of third pleonite, one oblique ruga extending from junction with fifth pleonite to junction with third on each side of pleonite; fifth pleonite smaller than fourth, lateral flanges small; sixth pleonite subpentagonal, lateral margins forming subtriangular projections, two short longitudinal grooves near articulation with telson, each groove joined to two much smaller transverse grooves. Female pleopods on second through fourth pleonites developed as three long and narrow articles, not developed on first and fifth pleonites; males without developed pleopods on first through fifth pleonites; uropods large, protopod subrectangular, endopod suboval, rounded, distal margin densely covered in setae, exopod suboval, more elongate, distal margin densely covered in setae.

Telson (Figs 6H , 8E ) lanceolate, lateral margins setose, slightly convex proximally, very slight notches at ~ 3/4 of length of telson, two short longitudinal grooves near junction with pleon, two long longitudinal ridges parallel to lateral margins of telson, distal end of telson subacute.

Coloration in life.

Carapace overall olive grey dorsally, lateral regions white, rugae extending across carapace white, posterolateral regions of carapace with few slim white longitudinal lines or small white blotches; lines and blotches usually restricted to posterolateral region, but some specimens possess one white longitudinal line along posterior 1/4 of carapace median line. Pleonal somites olive-grey anteriorly, white posteriorly, forming a pattern of alternating olive-grey and white stripes (Fig. 12A ).

Habitat.

Shallow infaunal, lives in wave swash zone of sandy beaches or shallow subtidal sandy flats where it burrows shallowly in sand, moves with tidal rise and fall.

Distribution.

Brazil: known from Maranhão, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, Bahia, Espírito Santo, and Rio de Janeiro.

Etymology.

The species name honors Alexandre O. Almeida, a valued friend and respected colleague who has contributed extensively to increase knowledge of the decapod crustaceans of Brazil.

Remarks.

Emerita almeidai sp. nov. is closest to E. portoricensis and thus shares a wide range of morphological similarities, which is why for many years several specimens from Brazil were wrongly assigned to E. portoricensis (see Introduction). Both species have a carapace densely covered by microcrenulate rugae (Figs 1A , 5D, G , 6B , 8A , 11 , 12 ) distributed in similar patterns, a front with three subacute lobes with the rostrum being distinctly shorter than lateral projections (Figs 5D, G , 6B ), first pereopod dactyli more than twice as long as wide and not as rounded as in other species such as Emerita brasiliensis and Emerita talpoida (Figs 5 , 6C, D ), two pairs of rugae extending onto lateral flanges of the first two pleonites. However, some characters such as the carapace length and width ratio (cw./cl.), the number of articles on the antennal flagellum, the first maxilla, the dactylus of the first pereopod, and the coloration in life can be used to distinguish between these two species. The carapace in E. almeidai sp. nov. (Figs 1A , 5D , 6B , 8A , 11 , 12A ) tends to be more oblong than that of E. portoricensis (Figs 5G , 12B ), usually being 1.42-1.54 × as wide as long in adult specimens (vs. 1.49-1.64 × in E. portoricensis , present study), although there is some overlap. The number of articles on the antennal flagellum of E. almeidai sp. nov. (Fig. 8D ) also tends to be more variable than that of E. portoricensis , varying from 74 to 104 articles in adult specimens, while E. portoricensis usually has 76-86 ( Felder et al. 2023; present study). Although there is still some overlap, this character is still useful to distinguish between the two species. However, juvenile specimens (see details in Materials and methods) may have many fewer articles on the antennal flagellum in both species, and thus this character is only useful for adult specimens. The first maxilla of E. almeidai sp. nov. (Fig. 9B ) also differs from that of E. portoricensis ( Felder et al. 2023: 349, fig. 3): in E. almeidai sp. nov. the proximal endite is wider, rounder and with more convex margins, and the endopodal palp is proportionally wider and shorter. The first pereopod dactylus (Figs 5D , 6D , 8B ) is also distinct, with E. almeidai sp. nov. having low, moderately and regularly spaced serrations on the inferior surface of the dactylus, while E. portoricensis has a slight and irregular serrations, which in many cases can be absent. The coloration of these two species can also be used to distinguish between live specimens. As shown in a recent redescription of E. portoricensis ( Felder et al. 2023: 345, fig. 1) and in the present work (Fig. 12B ), this species has very wide white bars on the posterolateral regions of carapace along with a wide white bar along the posterior 1/4 of the carapace median line. Although E. almeidai sp. nov. shares some of these characteristics (Fig. 12A ), the white bars are usually slimmer and the white bar along the carapace median line is usually absent; however, it was observed only in one freshly collected paratype specimen (MZUSP 43536). The white colored rugae, which were observed in all of the freshly collected specimens of E. almeidai sp. nov. (Fig. 12A ), however, are not present in either of the specimens shown in the recent redescription of E. portoricensis ( Felder et al. 2023: 345, fig. 1) or in the specimen analyzed in this study (Fig. 12B ), suggesting that this character might be unique to E. almeidai sp. nov. The southernmost record for E. portoricensis (Venezuela and Trinidad) and the northernmost record for E. almeidai sp. nov. ( Maranhão, Brazil) are very far apart and there is a strong marine barrier, the Amazon-Orinoco plume (see Curtin 1986 for physical characteristics) that can promote some isolation between northern and southern decapod populations (see Peres et al. 2022), and this is possibly the reason there are no records of these species coexisting in the same environment.

Emerita almeidai sp. nov. has been observed to co-occur with E. brasiliensis in Praia de Iriri, in the state of Espírito Santo, Brazil (CCDB 3992 and 7226), with specimens of both species being collected at the same locality and on the same day. The distribution of these two species overlaps along the coast of the states of Espírito Santo and Rio de Janeiro, and it is possible that they co-occur in more locations in these states. Emerita almeidai sp. nov. can be distinguished from E. brasiliensis by the shape of the dactylus, which is elongated and has a serrated ventral margin in E. almeidai sp. nov. (Figs 5D , 6D , 8B ) and ovate and non-serrated in E. brasiliensis (Figs 5C , 6C ). The dactylus length and width ratio (dl./dw.) is also a robust parameter to distinguish the two species, especially in individuals of similar size. In E. almeidai sp. nov., the dactylus is proportionally longer and narrower than that of E. brasiliensis . The front is also different (Figs 5C, D , 6C, D ): in E. brasiliensis the lateral projections and the rostrum are ca. as long as each other. The patterns of distribution of the microcrenulate rugae are also distinct between these two species (Figs 5C, D , 6A, B ), with E. almeidai sp. nov. having very dense and non-broken rugae across much of the carapace, while E. brasiliensis has rugae that are more broken into cusps ( Felder et al. 2023). Furthermore, the cw./cl. ratio is also useful to distinguish these two species since E. almeidai sp. nov. has an overall longer and narrower carapace when compared to E. brasiliensis . The antennae (Figs 6I, J , 8D ) is another character that can be used to distinguish between the two species, because E. almeidai sp. nov. has 74-104 articles, while E. brasiliensis has 103-134 articles; however, there is a small overlap. The differences between the telson measurements obtained between the telson length and width ratio (tl./tw.) showed a tendency for telson growth in E. almeidai sp. nov. in relation to the increase in carapace length, while in E. brasiliensis this ratio tends to remain stable with increasing carapace length. Melo (1999) did not highlight significant differences for this structure, but Calado (1990) described the telson of E. brasiliensis as being lanceolate, larger than the pleon, with all margins with short bristles, and that of E. almeidai sp. nov. with a triangular shape, larger than the pleon, wider in the proximal portion, with margins also supporting short bristles, which corroborates the biometric data found in our analyses.

The other species of Emerita found in the western Atlantic Ocean, E. talpoida and E. benedicti , are not known to co-occur with E. almeidai sp. nov.; Emerita talpoida can be distinguished from the new species by the rounded and ovate dactylus of the first pereopod (Fig. 5D, F ), while E. benedicti (Fig. 5B ) has a very acute terminus of the dactylus compared to a more subacute and slightly rounded terminus for E. almeidai sp. nov. The morphology of the first pereopod dactylus can also be used to distinguish the new species from other congeners in the Indian Ocean, Indo-Pacific and eastern Pacific.

Previous descriptions of mouthparts of species of Emerita are scarce, only existing for two species, E. talpoida and E. portoricensis (see Snodgrass 1952 and Felder et al. 2023). Thus, comparative studies of the mouthpart morphology of Emerita are lacking and could be of great importance. At least for E. almeidai sp. nov. and E. portoricensis , it has been noted that the morphology of certain articles of the mouthparts, in this case the first maxilla, can be successfully used to distinguish between species. Thus, future descriptions and redescriptions of species of Emerita should include such characters, which might be valuable for comparative taxonomic studies.

The number of species in the genus Emerita is now raised to 12, with five occurring in the western Atlantic ( E. almeidai sp. nov., E. benedicti , E. brasiliensis , E. portoricensis , E. talpoida ), five in the Indian Ocean or Indo-Pacific ( E. austroafricana , E. emeritus , E. holthuisi , E. karachiensis , E. taiwanensis ) and two in the Eastern Pacific ( E. analoga and E. rathbunae ). The actual number might even be higher, given that there is a large distribution hiatus between the populations of E. analoga from North and South America and genetic differences between the northern and southern populations of E. talpoida . The record of E. brasiliensis from Venezuela is doubtful and may be a misidentification or may represent a separate species given the large geographic hiatus (Fig. 7 ). All of these cases require a thorough study, as made herein for some congeners, to determine whether these actually represent different, yet very similar, species.

Figures

Figure 1. A dorsal view of adult ♀ of Emerita almeidai sp. nov. (CCDB 3369) B ventral view of adult ♀ of Emerita brasiliensis (CCDB 2552). The main characters used for external morphology analysis are labeled. Scale bar: 5 mm.

Figure 5. Dorsal view of carapace and rostrum / front, and lateral view of antenna / first pereopod of adult ♀ s of Emerita species from the Americas A Emerita analoga (CCDB 4870) B Emerita benedicti (CCDB 4674) C Emerita brasiliensis (CCDB 4615) D Emerita almeidai sp. nov. (CCDB 3369) E Emerita rathbunae (CCDB 1029) F Emerita talpoida (CCDB 4675) G E. portoricensis (CCDB 3525).

Figure 6. Comparative morphological characters observed in adult ♀ s of similar sizes between Emerita brasiliensis (CCDB 2552) and E. almeidai sp. nov. (CCDB 3026). Carapace shape: Dorsal view of A E. brasiliensis and B E. almeidai sp. nov.; Dactylus of first pereopod: Lateral view of C E. brasiliensis and D E. almeidai sp. nov.; Anterior region with rostrum, lateral spines, and ocular peduncle: Dorsal view of E E. brasiliensis and F E. almeidai sp. nov.; Posterior region / telson: Ventral view of G E. brasiliensis and H E. almeidai sp. nov.; Left ventral view of antenna I E. brasiliensis and J E. almeidai sp. nov.

Figure 7. The updated geographic distribution of Emerita brasiliensis, E. portoricensis, and E. almeidai sp. nov. according to the literature (Efford 1976; Melo 1999; Veloso and Cardoso 1999; Felder et al. 2023) and the present study.

Figure 8. Emerita almeidai sp. nov. A ♀ paratype, cl. 14.67 mm (CCDB 5855) B, E ovigerous ♀ paratype, cl. 15.01 mm (CCDB 4937) C, D ovigerous ♀ paratype, cl. 17.31 mm (CCDB 5855) A dorsal view B lateral view of dactylus of pereopod 1 C lateral view of left antennule D lateral view of left antenna E dorsal view of telson and uropods. Scale bars: 6 mm (A); 4 mm (B, E); 3 mm (C, D).

Figure 9. Emerita almeidai sp. nov. A-E ovigerous ♀ paratype, cl. 17.31 mm (CCDB 5855) F, G ovigerous ♀ paratype, cl. 15.01 mm (CCDB 4937) A right mandible B left first maxilla C right second maxilla D left first maxilliped E left second maxilliped F right third maxilliped external face G right third maxilliped internal face. Scale bars: 1 mm (A-D); 4 mm (E-G).

Figure 10. Emerita almeidai sp. nov. A, D ovigerous ♀ paratype, cl. 17.31 mm (CCDB 5855) B, C, E ovigerous ♀ paratype, cl. 15.01 mm (CCDB 4937) A lateral view of right pereopod 1 B lateral view of left pereopod 2 C lateral view of left pereopod 3 D lateral view of left pereopod 4 E lateral view of right pereopod 5. Scale bars: 4 mm (A); 2 mm (B); 5 mm (C); 3 mm (D); 1 mm (E).

Figure 11. Emerita almeidai sp. nov. A ovigerous ♀ holotype, cl. 13.52 mm (CCDB 7233) B ♂ paratype, cl. 7.29 mm (MZUSP 43536) C ♀ paratype, cl. 10.49 mm (MOUFPE 20112) D ♀, cl. 10.20 mm (CCDB 3369). Scale bars: 4 mm (A, B); 2 mm (C); 5 mm (D).

Figure 12. Fresh coloration of Emerita almeidai sp. nov., E. portoricensis and E. brasiliensis A E. almeidai sp. nov., ovigerous ♀ (not deposited), live specimen, Porto de Galinhas, PE, Brazil B E. portoricensis, ♀ (CCDB 3525), freshly collected specimen, Boca del Drago, Panama C Emerita brasiliensis, ♀ (CCDB 7301), freshly collected specimen, Praia de Guaratuba, Bertioga (SP), Brazil. Coloring details: 1. Thin white stripes on posterolateral portions of carapace; 2. Rugae clearly surrounded by white coloration; 3. Striped pattern on pleon; 4. Wide white bars on posterolateral portions of carapace; 5. White bar along posterior 1 / 4 th of median line of carapace; 6. Striped pattern on pleon; 7. Olive brown or brownish white color overall; 8. Rugae broken into cusps; 9. Absence of striped pattern on pleon.