Minuca panema (Coelho, 1972): Resurrection of a Fiddler Crab Species from Brazil Closely Related to Minuca burgersi (Holthuis, 1967) (Crustacea, Decapoda, Brachyura, Ocypodidae)

© 2023 Academia Sinica, Taiwan Open Access Minuca panema (Coelho, 1972): Resurrection of a Fiddler Crab Species from Brazil Closely Related to Minuca burgersi (Holthuis, 1967) (Crustacea, Decapoda, Brachyura, Ocypodidae) Carl. L. Thurman1, Hsi-Te Shih2,* , and John C. McNamara3,4 1Department of Biology, University of Northern Iowa, 1227 West 27th St., Cedar Falls, IA 50614-0421, USA. E-mail: [email protected] (Thurman). Tel: +1 319 273-2276 2Department of Life Science and Research Center for Global Change Biology, National Chung Hsing University, Taichung 402, Taiwan. *Correspondence: E-mail: [email protected] (Shih). Tel/Fax: 886-4-22856496 3Departamento de Biologia, FFCLRP, Universidade de São Paulo, Ribeirao Preto 14040-901, Brazil. E-mail: [email protected] (McNamara). Tel: +55 16 3315 3687 4Centro de Biologia Marinha, Universidade de São Paulo, 11600-000 SP, Brazil Received 6 November 2022 / Accepted 9 July 2023 / Published 13 September 2023 Communicated by Benny K.K. Chan We redescribe a species of fiddler crab, Minuca panema (Coelho, 1972), from the Atlantic coast of South America. It is closely related to M. mordax (Smith, 1870), and until now, the taxon has been considered to be synonymous with another closely related species Minuca burgersi (Holthuis, 1967). However, we found that two clades of M. burgersi sensu lato were restricted to the Caribbean Basin. This distribution differs from than that of M. panema, which occurs primarily along the eastern coast of South America, ranging from the island of Trinidad to Praia da Armação, Santa Catarina, Brazil. Based on our field studies, the geographical boundary between M. burgersi sensu stricto and M. panema is the Tobago Basin, north of Trinidad. Since the two species diverged only 3 to 4 million years ago, as dated from the phylogeny of the genus Minuca Bott 1954, there are few reliable morphological features that can be used to distinguish them clearly. In live crabs, there is a striking difference in coloration between the cherryred South American M. panema and the rusty-red Caribbean M. burgersi sensu lato. In males, the pattern of tubercles on the inner surface of the major cheliped varies between the two species. In females, the vulva is slightly larger in M. burgersi sensu stricto. Ocean tides and currents together with siltation owing to freshwater outflow from the Amazon and Orinoco rivers most likely have driven the divergence of these species. In the Caribbean, small tidal amplitudes have minimized long-distance gene flow in M. burgersi sensu stricto from isolated insular lagoons. In contrast, large tidal amplitudes and exposed habitats on riverbanks along the eastern Atlantic coast of South America have enabled long-distance dispersal in M. panema. DNA analysis reveals that haplotypes of cytochrome c oxidase subunit 1 are not shared between the species. Since natural selection and/or genetic drift have yet to produce extensive morphological divergences between M. panema and M. burgersi sensu stricto, we speculate that changes in the genes regulating mitochondrial DNA functions have led to speciation at the molecular level. According to the mitonuclear compatibility concept, we propose that mitochondrial DNA may be at the forefront of speciation events and that co-evolved mitonuclear interactions are responsible for some of the earliest genetic incompatibilities arising among isolated populations. Key words: Morphology, 16S rDNA, 28S rDNA, Cytochrome c oxidase subunit I (COI), Biogeography Citation: Thurman CL, Shih HT, McNamara JC. 2023. Minuca panema (Coelho, 1972): resurrection of a fiddler crab species from Brazil closely related to Minuca burgersi (Holthuis, 1967) (Crustacea, Decapoda, Brachyura, Ocypodidae). Zool Stud 62:45. doi:10.6620/ZS.2023.62-45. Zoological Studies 62:45 (2023) doi:10.6620/ZS.2023.62-45 1 © 2023 Academia Sinica, Taiwan BACKGROUND Fiddler crabs are common inhabitants of intertidal and supratidal regions around the world. Found along most temperate and tropical shores, these brachyurans exhibit substantial species diversity. Currently, there are 107 identified species of fiddler crabs (Shih et al. 2016 2018 2019a; Shih and Poupin 2020). Previously, all fiddler crabs were classified within a single genus, Uca Leach, 1814 (Rathbun 1897 1918; Crane 1975). Based on mitochondrial and nuclear DNA, Shih et al. (2016) accepted 11 genera of fiddler crabs as valid, supported further by mitogenomics (Conrad et al. 2021; Liu and Shih 2022) and larval morphology (Kumar and AlAidaroos 2022; Zhang and Shih 2022). This proposal has been adopted by most investigators and by the World Register of Marine Species (WoRMS) (Shih and Chan 2022). Along the shores of the western Atlantic Ocean, from Cape Cod, Massachusetts to Buenos Aires, Argentina, 20–21 species are currently recognized (Shih et al. 2016). Until 1939, only 14 species could be identified with certainty across regions in the western Atlantic (Rathbun 1918). At that time, Oliveira (1939) added three new taxa from the southeastern Brazilian coast near Rio de Janeiro: Uca olympioi, Uca salsisitus and Uca pugnax brasiliensis. Crane (1943) described Uca cumulanta from the Gulf of Paria near Capure, Pedernales, Venezuela. In 1967, Holthuis described Uca burgersi (= Minuca burgersi) (Fig. 1) specifically from Curaçao but acknowledged that the species was common throughout the Caribbean, from Florida to Mexico and south to Trinidad and Tobago. A related taxon, Uca panema Coelho, 1972, from Brazil was proposed five years later. In the northern Gulf of Mexico, three new species were described: Uca virens Salmon & Atsaides, 1968, Uca longisignalis Salmon & Atsaides, 1968 and Uca panacea Novak & Salmon, 1974. On the eastern coast of Mexico, Uca marguerita Thurman, 1981 was distinguished from the older, established taxa, U. burgersi, Uca mordax (Smith, 1870), Uca rapax (Smith, 1870) and Uca spinicarpa Rathbun, 1900. The last species described in the region based on morphology was Uca victoriana von Hagen, 1987 from southeastern Brazil. In Crane’s monograph (1975), taxonomic revisions were proposed for some species in the western Atlantic. In particular, the three species of Oliveira (1939) were found to be junior synonyms of older taxa. Crane considered U. olympioi and U. pugnax brasiliensis to be Uca uruguayensis Nobili, 1901 and U. rapax, respectively. Later, Tavares and de Mendonça (2003) questioned the validity of U. salsisitus as a species since the type specimens consisted of both U. rapax and Uca vocator (Herbst, 1804). Regarding “Ciecie Panema” in Marcgrave (1648: 185), Herbst (1782: 81) considered the species to be Cancer vocans minor Herbst, 1782 (= Gelasimus annulipes H. Milne Edwards, 1837; see Shih et al. 2021). However, the identity of the species was uncertain (Lemos de Castro 1962; Tavares 1993). Coelho (1972) provided a preliminary description of a new species, Uca panema, collected from Itamaracá Island, Pernambuco, Brazil, for Marcgrave’s (1648) “Ciecie Panema”. In her monograph, Crane (1975) reported M. burgersi to range from Florida, the Yucatan Peninsula, Belize, Guatemala, Panama and throughout the Caribbean islands to Venezuela. For the first time, she added specimens of M. burgersi sensu lato from Fortaleza (USNM 138509), Rio de Janeiro (USNM 136511) and São Sebastião (USNM 1136004, 138510), Brazil. Crane’s treatment led to the recognition of U. panema as a junior synonym of M. burgersi in Brazil. Fig. 1. A: Minuca panema (Coelho, 1972) and B: Male Minuca burgersi (Holthuis, 1967). A: From the South Atlantic Ocean – Brazil, São Paulo state, Caraguatatuba, Praia da Enseada (23.726°S, 45.419°W) (ZMUSP 20835). B: From type location, Caribbean – The Netherlands Antilles, Curaçao, Westpunt, Grote Knip, salt pond (12.352°N, 69.15122°W) (UNI 721). Scale bar = 10 mm. page 2 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan In 1980, von Hagen examined specimens of U. panema and wrote to Coelho that they were identical to U. burgersi, suggesting they were synonymous (pers. com., Jesser Fidelis de Souza Filho, Oceanography Museum, Federal University of Pernambuco (MOUFPE)). Coelho persisted in acknowledging the species (Coelho and Coelho-Filho 1993). However, Coelho dropped the name and began using M. burgersi instead (Coelho 1995; Almeida and Coelho 2008; Coelho et al. 2008; Almeida et al. 2010). Neither the designated type specimen nor the paratypes for U. panema as stipulated by Coelho (1972) are currently available at MOUFPE. Melo (1996) published a guide to the brachyurans of the western Atlantic and indicated that M. burgersi is distributed from Florida and the Gulf of Mexico to northern South America. There is no mention of U. panema. Melo reported U. burgersi to be absent from Guyana, Suriname and French Guiana as well as from locations in Brazil north of the Amazon estuary. Minuca burgersi appears again along the Brazilian coast from Sāo Luis, Maranhāo to Cabo Frio near Rio de Janeiro. Consequently, the species’ range is not continuous but is disrupted by the silty freshwater outflow from the Amazon and Orinoco Rivers. Thurman’s et al. (2021) molecular study revealed three clades showing minor morphological differences within the Minuca burgersi species complex. “Clade 3” includes samples from the type locality of Uca burgersi Holthuis, 1967 (Grote Knip, Westpunt, Curaçao) which should be considered the true M. burgersi. “Clade 1” is distributed along the Atlantic shores of South America and includes the type locality of Uca panema Coelho, 1972 (Itamaracá Island, Pernambuco, Brazil). Although Uca panema has been synonymized as Uca burgersi since 1995 (e.g., Coelho 1995; Almeida and Coelho 2008; Coelho et al. 2008), the minor morphological differences are now supported by molecular evidence (Thurman et al. 2021) and the species can be considered a pseudocryptic species (e.g., Ragionieri et al. 2009; Shih et al. 2018; Fratini et al. 2019; Prema et al. 2022). In this article we redescribe in detail the characters of Uca panema Coelho, 1972 as a species closely related to both M. mordax and M. burgersi sensu lato. Because the holotype of Uca panema cannot be located (see above) and the species is similar to M. burgersi and M. mordax, it is necessary to designate a neotype to resolve issues of doubtful identity and to maintain nomenclatural stability (see ICZN 1999: Art. 75, Art. 75.3, Art. 75.3.4). We have selected a neotype male specimen from the Rio Maracaípe, Pernambuco, Brazil (latitude ≈ 8.5°S), which is near the original type locality (Itamaracá Island, Pernambuco, Brazil; latitude ≈ 7.8°S) (see ICZN 1999: Art. 75.3.6). Here, we distinguish Minuca panema from M. burgersi sensu stricto in the southeast Caribbean (Fig. 2). Minuca aff. burgersi will be analyzed in a forthcoming publication. MATERIALS AND METHODS Sampling A total of 1,060 preserved specimens from 39 locations along the shores of the western Atlantic Ocean between the Bahamas and southern Brazil (Table S1) was examined. Based on previous observations (Thurman et al. 2021), the specimens were separated into two geographical groups (see below) depending upon whether they were collected north or south of the Tobago Strait (11.000°N latitude). For the northern locations, 504 specimens were collected from 19 sites across the Bahamas, Puerto Rico, U.S. Virgin Islands, Netherlands Leeward Islands, Barbados, Netherlands Antilles and Tobago (“Clade 3” in Thurman et al. 2021). For the southern populations (“Clade 1” in Thurman et al. 2021), 556 specimens of M. burgersi-like crabs were examined from 20 locations along the Atlantic coast of South America. Specimens were captured from Trinidad, and the coastal states of Brazil (Ceará, Paraíba, Pernambuco, Bahia, Espírito Santo, Rio de Janeiro, Paraná and Santa Catarina) (Table S1). Freshly collected crabs were frozen, preserved in 80% ethanol and deposited into the collections housed at the Department of Biology, University of Northern Iowa (UNI) or at the Zoological Museum, University of São Paulo (ZMUSP). Voucher specimens of M. burgersi were examined at the National Museum of Natural History, Washington, DC, USA (USNM), the Zoological Museum, University of São Paulo, São Paulo, Brazil, and the Rijks Museum, Leiden, the Netherlands (RMNH) to authenticate the morphological characteristics of the specimens. Additional materials from zoological collections held at the Department of Life Science, National Chung Hsing University, Taichung, Taiwan (NCHUZOOL); Senckenberg Museum, Frankfurt am Main, Germany (SMF); Museo Zoológico de la Universidad de Costa Rica, San José (UCR); and the Zoological Reference Collection of the Lee Kong Chian Natural History Museum, National University of Singapore, Singapore (ZRC) were included in the molecular study. Morphology Previously we provided a morphometric examination of U. burgersi from the Caribbean and South America (Thurman et al. 2021). All measurements taken to the nearest 0.01 mm were obtained with page 3 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan 0 700 1,400 2,100350 Miles Brazil Argentina Bolivia Peru Colombia Venezuela Atlantic Ocean Pacific Ocean Mexico United States M. panema M. burgersi M. aff.burgersi Fig. 2. Geographical distribution of Minuca burgersi (Holthuis, 1967) (blue; distributed Bahamas, Curaçao, Barbados), M. aff. burgersi (green; distributed Florida, Virgin Islands, Belize) and M. panema (Coelho, 1972) (red; Atlantic coast of South America: Trinidad Island to Florianópolis, Santa Catarina, Brazil). Modified from Thurman et al. (2021). N page 4 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan digital calipers (Fowler Sylvac, Switzerland). The terminology of Crane (1975) was used to describe the anatomical structures of the crabs. Characteristics of the male first gonopod (G1), vulva, carapace, thoracic sternum, cheliped and ambulatory legs were examined in detail with an Olympus ST-SZ binocular dissecting microscope (Olympus Corporation, Tokyo, Japan). Macroscopic structures were photographed with a Nikon D40 digital camera and a zoom micro-lens (Nikkor AF-S, F1:2.8G). Structural details were recorded using a Zeiss Stemi 305 digital microscope and Jenoptik GRYPHAX (V2.1.0.725) software (Carl Zeiss Gmbh, Jena, Germany). Adobe Photoshop CC 2020 was used to process the digital images. An ocular micrometer was used to estimate the size of microscopic structures. Molecular analyses To analyze mitochondrial 16S and cytochrome c oxidase subunit 1 (COI) haplotypes, crabs were collected from 12 locations in the eastern Caribbean and 12 locations in Brazil (see Thurman et al. 2021: Table 1; Fig. 2). Additional 16S and COI sequences for M. marguerita were obtained with primers 16H10, 16L29, LCO1490 and HCO2198 (see Schubart 2009). The nuclear 28S sequences were obtained from M. argillicola (Crane, 1941), M. burgersi, M. aff. burgersi, M. marguerita and M. panama with the primers 28L4 Table 1. Haplotypes of 16S rDNA, COI and 28S rDNA markers for species of Minuca and related outgroups Locality Catalogue # NCHUZOOL (unless indicated) Access. # for 16S Access. # for COI Access. # for 28S M. argillicola Ecuador: Puerto Morro SMF 34737 LC150346 FN430701 FN430713 Brazil: Rio de Janeiro 13956 LC150347 LC150407 LC150476 M. burgersi Puerto Rico: Río de la Plata UNI 2729 MW310201 MW311060 OQ476644 Barbados: St. Lucy: Maycocks Bay UNI 3345 MW310199 MW311063 Curaçao: Charo UNI 3276 MW310204 MW311060 M. aff. burgersi USA: Florida UNI 486 MW310192 MW311051 Bahamas: San Salvador: Salt Pan ZRC LC087920 LC087950 M. ecuadoriensis Ecuador: Puerto Morro SMF 34740 LC150348 FN430704 FN430716 M. galapagensis Ecuador: Puerto Morro SMF 34741 LC150349 FN430705 FN430717 Peru: Tumbes SMF 13151 LC150348 FN430704 FN430716 M. herradurensis Panama: Diablo Heights mangroves 13580 AB813664 AB813680 AB813709 “M. longisignalis” Texas, USA: Ingleside Cove, Corpus Christi 13938 LC087922 LC087952 LC087979 M. marguerita Mexico: L. La Mancha, Veracruz 15166 OQ456151 OQ456152 OQ476645 M. minax Virginia, USA: Chesapeake Bay 13939 LC087921 LC087951 LC087978 Florida, USA 13957 LC150350 LC150408 LC150477 M. mordax Brazil: São Paulo 13940 LC087923 LC087953 LC087980 M. osa Costa Rica: Golfo Dulce UCR 2620-01 LC150351 FN430711 FN430722 M. panema Trinidad and Tobago: Maracas Bay Village UNI A3464 MW310187 MW311039 OQ476647 Brazil: Ceará: Fortaleza UNI 2401 MW310189 MW311043 OQ476648 M. pugnax (#1) Maryland, USA: Assateague I. 13941 LC087924 LC087954 LC087981 (#2) Maryland, USA: Assateague I. 13941 LC087925 LC087955 LC087982 M. rapax Jamaica: Trelawny 13942 LC087926 LC087956 LC087983 British Virgin: Paraquita Bay 13943 LC087927 LC087956 LC087984 Panamá: Bocas del Toro 13944 LC087928 LC087957 LC087984 M. victoriana Brazil: Bahia 13945 LC087929 LC087958 LC087985 M. virens(#1) Texas, USA: Ingleside Cove, Corpus Christi Bay 13584 AB813665 AB813681 AB813710 (#2) Texas, USA: Ingleside Cove, Corpus Christi Bay 13584 LC087930 AB813681 LC087986 Florida, USA: Money Bayou, Gulf County 13946 AB813665 AB813681 LC087984 M. vocator Brazil: Ceará 13948 LC087931 LC087959 LC087987 Trinidad SMF 34745 LC150352 FN430709 FN430720 M. zacae El Salvador SMF 2104a LC150353 FN430710 FN430721 Outgroups Leptuca pugilator South Carolina, USA: Georgetown 13586 AB813662 AB813678 AB813707 Petruca panamensis Panamá: Culebra I. USNM 1294205 (neotype) LC087917 LC087943 LC087975 page 5 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan and 28H4 (Ragionieri et al. 2009) (Table 1) following Shih et al. (2016). Other 28S sequences for Minuca species were taken from Shih et al. (2016) and are included in table 1. A phylogeny for 16 species of Minuca collected from 31 locations in the Gulf of Mexico, the western Atlantic Ocean and the Pacific Ocean was constructed employing DNA sequences from 16S, COI and 28S genes, with Leptuca pugilator (Bosc, 1802) and Petruca panamensis (Stimpson, 1859) serving as the outgroups. For the combined 16S, COI and 28S dataset, the best-fitting models for sequence evolution of individual datasets were determined using PartitionFinder (vers. 2.1.1, Lanfear et al. 2017) selected by using the Bayesian information criterion (BIC). The best models for the three individual datasets were all GTR+G+I and were subsequently employed for Bayesian inference (BI) analysis. The BI was performed with MrBayes (vers. 3.2.6, Ronquist et al. 2012). The search was run with four chains for 10 million generations and four independent runs, trees being sampled every 1,000 generations. The convergence of chains was determined by the average standard deviation of split frequency values below the recommended 0.01 (Ronquist et al. 2020); the first 800 trees were discarded as the “burn-in”. RESULTS TAXONOMY Family Ocypodidae Rafinesque, 1815 Subfamily Gelasiminae Miers, 1886 Genus Minuca Bott 1954 Minuca panema (Coelho, 1972) (Figs. 1, 3–7) Ciecie panema Marcgrave 1648: 185 (list; Brazil). Cancer vocans minor Herbst 1782: 81 (= Gelasimus annulipes H. Milne Edwards, 1837; see Shih et al. 2021) (not Gelasimus annulipes H. Milne Edwards, 1837). Uca panema Coelho, 1972: 42 [Pernambuco, Paraíba]; Coelho and Coelho-Filho 1993: 48 [key; Brazil]; Coelho 1995: 139 [list]; Shih et al. 2016: 154 [list]; Questel 2019: 28 [list]. Uca (Minuca) burgersi – Crane 1975: 168–172, 604 [part, list; Brazil]; Almeida et al. 2010: 354 [Brazil]; Bezerra 2012: 216–219 [part, list; Brazil]; Thurman et al. 2013: 6, 8, 9, fig. 1 [list; Brazil]. Uca burgersi – von Hagen 1983: 230 [part; Brazil]; von Hagen 1984: 205 [Trinidad]; Almeida and Coelho 2008: 207 [Brazil]. Minuca burgersi – Shih et al. 2016: 143, 154, fig. 3; Thurman et al. 2017: 247–250, tables 1–5, figs. 3, 5, 6, [Brazil]; Rosenberg 2019: 735 [list]; Thurman et al. 2021: 1–28 [South America]. Material examined: Minuca panema (Table S1): Neotype: male 11.55 × 8.24 mm (MZUSP 42510), Brazil, Pernambuco, Rio Maracaípé. Others: Trinidad: (RMNH 23040), Blanchisseuse (USNM 138505), L. Ebranche River (RMNH 23040, UNI 722), Burro River, Invader’s Bay (UNI 721, 720), Cocorite Swamp (USNM 137745); Brazil: Pará, Curuçá (MZUSP 12313); Maranhão, Icatú (MZUSP 23176); Ceará, Fortaleza (USNM 138509) (MZUSP 23179); Paraíba, Mamanguape (MZUSP 13255); Pernambuco, Rio Maracaípé (MZUSP 20838 and 20841); Bahia, Itaparica (USNM 138510), Madre de Deus: Plataforma Lobato (MZUSP 20834, 20844); Espírito Santo: Conceição (MZUSP 18650), Anchieta (MZUSP 18638), Santa Cruz: Bairro Joana D’Arc: Guarapari (MZUSP 20837, 20840, 20842, 20990, 20991); Rio de Janeiro: Ilha do Pinheiro (USNM 138511), Ilha de Paquetá (USNM 19971), Itacuruçá (MZUSP 17201), Barra de Guaratiba (MZUSP 20839); São Paulo: Ilhabela (USNM 136004), Santos (USNM 138512), São Sebastião, Bertioga (USNM 1136004, MZUSP 20834, 20835, 20839, 23177, 23178); Paraná: Baía de Guaratuba: Ponta de Venda (ZMUSP 42511), Baía de Guaratuba (MZUSP 20833); Santa Catarina: Rio Itajaí-Mirim: Balneário Daniela: Barra da Lagoa: Praia da Armação (MZUSP 20828, 20829, 20830, 20831, 20832). Comparative material: Minuca burgersi (Holthuis, 1967) (Table S1): Netherlands Antilles: Curaçao: Grote Knip (RMNH 23012 (holotype); USNM 121099 (paratype), 7577; UNI 719); Aruba (USNM 138503); Leeward Islands: Sint Maarten (USNM 138497, 138498); Tobago: Pigeon Point (USNM 138504); Barbados, St. Peter’s Bay, Maycock’s Bay, Graeme Hall (UNI 716, 717, 718). Description (Fig. 3): Carapace trapezoidal, surface strongly convex, smooth and glossy with numerous small pits. Front angled from midline to lateral margin about 16°. Eyebrows barely visible (Fig. 3A: a). Length of carapace 68% width in females (n = 108) and 66% in males (n = 401). H-depression deep with some pubescence and two large central pores in sulcus. Frontal region compared to carapace width 37.1% or greater (n = 10). Sulcus posterior to orbits deep (Fig. 3A: b). Lower orbital margin with rectangular dentals (Fig. 3F: c). Anterolateral angles (Fig. 3A: d, Fig. 3B: d) sharp, pointed inward toward medial line. Hepatic area swollen and rounded behind angle. Anterior edge of lateral line almost straight forming smooth, obtuse angle with posterior lateral line (Fig. 3B: e). Two posterolateral striae (Fig. 3B: f) present. Dorsal striae long and fragmented into two parts. Second more ventral and shorter. Patch of pubescence (Fig. 3B: g) between striae and ventral edge of carapace. Outer surface of major cheliped with dorsal ridge on manus. Large tubercles on upper manus decreased in size to ventral margin (Fig. 3C). Dactyl articulation joint (Fig. 3C: h) page 6 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan with row of tubercles. Base of pollex at manus forming smooth triangular sulcus (Fig. 3C: i). Pollex (Fig. 3C: j) and dactyl (Fig. 3C: k) horizontally compressed, blade like with smooth surfaces. Three rows of tubercles in gap. End of pollex trifurcated with three tooth-like tubercles. Dactyl with two larger tubercles (Fig. 3C: k, Fig. 4A: a); one proximal and the other distal. Pollex with large tubercle on distal half followed by second smaller tubercle (Fig. 3C: j). Inner surface of major cheliped with carina of tubercles lining dorsal edge of carpal cavity (Fig. 3D: l). Carina often ending in a patch of tubercles with upper row pointed to dactyl. A smooth triangular area above the carina terminus. Lower edge of carpal cavity with apex of tubercles at proximal end of oblique ridge (Fig. 3D: m). Distally oblique ridge across palm undeveloped. Dactyl joint with row of 5–8 tubercles (Fig. 3D: o). Lines of tubercles on predactyl and articulating ridges not parallel. Predactyl ridge Fig. 3. Minuca panema (Coelho, 1972) (ZMUSP 20833). A: Dorsal view. B: Lateral carapace view on side of minor cheliped. C: Outer surface of major cheliped. D: Inner surface of major cheliped. E: Second ambulatory leg. F: Oral view of carapace. a. eyebrow, b. postorbital sulcus, c. dental on suborbital margin, d. anterolateral angle, e. posterolateral line, f. posterolateral striae, g. pubescence, h. articulation ridge, i. pre-pollex depression, j. pollex, k. dactyl, l. superior carpal cavity carina, m. apex of oblique ridge, n. pre-dactyl ridge, o. articulation ridge, p. manus-pollex ridge, q. pubescence, r. setae. Scale bar = 10.0 mm. page 7 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan forming crescent arch initially extending toward palm but returns to articulation (Fig. 3D: n). Keel on lower edge of manus and ventral pollex. Exterior surface of minor cheliped smooth. Long ridge from manus to end of pollex. Dactyl with faint ridge from articulating junction to terminus. Pollex and dactyl with 6–8 sawtooth tubercles in gap. Distal tips of dactyl and pollex with sharp, chitinized edge. On inner surface of pollex and dactyl, distal end with regularly arranged comb-like setae covering about one-third of pollex length. Width of merus on ambulatory legs 1–3 of minor side (Fig. 3E) approximately 37% of length (n = 10). Dorsal and lateral surfaces of carpus and manus on ambulatory legs 1–3 of with pubescence (Fig. 3E: q). Dorsal surface of dactyl without pubescence. No pubescence on ventral surface of manus, carpus or dactyl. Long setae (Fig. 3E: r) plentiful on manus but sparse on merus. Distal end of G1 with long setae (Fig. 5A: a, b; Fig. 5B, C). Proximal group few in number but long (0.5 to 0.75 mm) (Fig. 5C). A few setae near terminal flange. Flange with pronounced cusp (Fig. 6A: a; Fig. 6B: a). In females, operculum of vulvae small and protruding, no tubercle (Fig. 7A). Remarks (Figs. 4, 7; Table 2): The relationship of M. panema to other species in the Minuca genus is addressed in the “DISCUSSION” section. Since they are geminate species, here, we focus on the subtle anatomical landmarks distinguishing M. panema from M. burgersi sensu stricto (Table 2). For males, there are two or three large tubercles (Fig. 4A: a) at the distal end of the cheliped pollex in M. panema. In M. burgersi sensu stricto, there is usually only one tubercle (Fig. 4B: a) on the pollex. Minuca panema has a prominent smooth sulcus on the lateral surface of the major cheliped at the pollex-manus junction (Fig. 4A: b). Tubercles on the lateral surface of the manus form a distinct pre-dactyl ridge (Fig. 4A: c) in M. panema. In M. burgersi, the ridge is weak (Fig. B: c). On the medial inner surface of cheliped, oblique tubercle ridges are more clearly defined in M. panema (Fig. 4C: d). The carina (Fig. 4C: e) along the lower edge of the carpal cavity are more distinct in M. panema. The carina along the upper edge of the carpal cavity terminates in a tubercle field (Fig. 4C: f) that expands to the medial predactyl ridge. The pre-dactyl ridge (Fig. 4C: g) arches strongly and intersects with the tubercle ridge on the swelling of at the articulating joint in M. panema. In M. burgersi, the oblique ridge (Fig. 4D: d) is less developed and the inferior carpal carina has only a few tubercles (Fig. 4D: e). The field of tubercles at the distal end of superior carpal carina (Fig. 4D: f) does not extend to the pre-dactyl ridge. This area is usually smooth. Figures 5 and 6 are images of the right G1 from Minuca panema and M. burgersi. In figure 5, the former, G1 is ornamented with setae that have been removed in figure 6. In M. panema, setae near G1 tip (Fig. 5A–C) Fig. 4. Comparison of male major cheliped between Minuca panema (Coelho, 1972) (A, C; MZUSP 20833) and M. burgersi (Holthuis, 1967) (B, D; UNI 719). A, B: outer surface, C, D: inner surface. a. tubercle at distal end of pollex, b. sulcus at pollex-manus junction, c. lateral predactylar tubercle ridge, d. oblique palmar tubercle ridge, e. anterior of carpal cavity, f. tubercle field, g. medial predactylar ridge. Ruler with 1 mm divisions at upper edge of figure 5A, B. page 8 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan Table 2. Comparison of morphological landmarks between Minuca panema and Minuca burgersi sensu stricto Characters M. burgersi M. panema Eye orbits From dorsal view, ocular cavities angled to posterior. Eyebrows visible. Dorsal carina lightly beaded, lower strongly beaded. Ocular cavities not strongly angled. Eyebrows visible. Upper and lower carina almost smooth. Carapace surface Surface finely granular with pits. Post-orbital sulcus deep. Medially with tubercle. Laterally curved to intersect dorsal lateral margin. H-depression deep. Interocular lobe formed about 34.0 ± 1.3% of carapace width. Eyestalks short with 25% retina. From front, carapace arched. Surface finely granular with pits. Post-orbital sulcus deep. Medial end curving toward H-depression. Large tubercle at anteroand medial sulcus. H-depression shallow. Interocular lobe 37.8 ± 3.0% carapace width. Eyestalks like M. burgersi. From front carapace flat. Orbital floor Floor smooth. Lateral ends with 3-sharp tubercles surround by short setae. Lower edge with rectangular dentals. Setae behind dentals. Floor smooth. Lateral ends with 2-tubercles. Lower edge with rectangular dentals. Setae behind line of dentals. Anterolateral angle Anterolateral angles pointed forward but converging toward body midline. Same as M. burgersi. Anterolateral, dorsolateral and vertical lateral margins Anterolateral margins intersecting with dorsolateral margin at widest portion of carapace. Lines almost smooth. 2 posterolateral striae present. Anterolateral margins diverging into vertical lateral margin. This terminating between 3rd and 4th ambulatory legs. Margin lines strongly tuberculated. Otherwise margins very similar. Major cheliped outer surface Outer surface: Dorsal surface with two parallel ridges of tubercles. Outer upper surface with large tubercles decreasing in size ventrally. Ventral margin with a tubercle ridge. Parallel tubercle ridges on dorsal surface weakly developed. Sulcus at pollex-manus junction. predactylar ridge Predactylar articulation joint weakly developed. No tubercles on predactylar joint. pollex Pollex face smooth with pits. One tooth about 2/3 distance of pollex. Terminus with 3 teeth. 3 rows of teeth on dorsal edge of pollex. Teeth on dorsal edge of pollex same as M. burgersi. dactyl Dactyl blade-like with variable number of teeth in gap and no grooves. Rows of tubercles on anterior and posterior edge. Random teeth between. Dactyl blade-like and smooth. Others same as M. burgersi. inner dactyl At articulation, 2 predactylar ridges diverging dorsally. Surface smooth. 2 diverging predactylar ridges. Surface smooth. inner palm surface Dorsal carina completely outlining carpal cavity. Tubercle ridge diverging point to dactyl. Triangle above carina smooth. Palm with high tubercle ridge running obliquely. Carpal carina ending in a patch of 10–20 large tubercles above apex of oblique ridge. Few tubercles connecting apex and carina. Minor chela Dorsal surface with ridge. Outer surface smooth. Depression below dactyl articulation. Strong line on pollex. Teeth in gap small. Distal 3–4 largest. Distal end of minor claw ridged and sharp. Inner surface smooth. 4–5 long setae on distal end of pollex. Carpus with numerous vertical lines of tubercles on posterior face. Merus with numerous rows of vertical tubercles on posterior surface. Outer surface smooth. Dorsal surface of dactyl with small ridge. Pollex with Ridge. 3–5 teeth in gap. Tip of pollex and dactyl rigid and sharp. Inner palm smooth. Long setae on inner faces of both dactyl and pollex. Carpus smooth. Merus with short row of tubercles. stridulation ridges on 1st ambulatory leg Face of adjacent 1st ambulatory leg without stridulating apparatus. No obvious stridulation apparatus on 1st ambulatory leg. Ambulatory legs Manus and carpus with pubescence and long setae on dorsal surface. Merus and ischium with short setae. Longer setae on ventral surface. Merus width about 1/3 segment length. Dorsal surface of manus and carpus wit pubescence and long setae. No pubescence on 4th ambulatory leg. Ventral surface smooth with long setae. Proximal merus with short setae. G1 (Crane 1975: fig. 66F) G1 with setae near terminus. Terminal flange dark and semicylindrical. Pre-terminal palp present. Few long setae. Deep cusp in flange. Vulva (Crane 1975: fig. 54G) Sternal opening covered by bulging plate. No protruding tubercle. Sternal opening covered by bulging plate. No protruding tubercle. Live color carapace Dorsal carapace surface purple to brown. H-depression large, redbrown. Lower carapace dark chocolate brown. Dorsal surface gray with white spots. H-depression thin, bright red. Lower carapace cherry red-brown. cheliped Cheliped dark red-orange. Fingers off-white. Cheliped yellow-orange. Fingers light in color. ambulatory legs Legs brown, carpus and manus banded. Legs proximally red, distally light brown tan. page 9 of 26 Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan originate in estuarine habitats inundated by strong semidiurnal tides of 2 to 4 m amplitudes along the eastern coast of South America (Thurman et al. 2021). In contrast, tides across the Caribbean islands are smaller in amplitude (0.34 to 0.85 m) and their currents are weaker. The tenuous tides of the Caribbean are known to alter seasonal reproduction in fiddler crabs (Morgan and Christy 1994). The diameter of ova in M. burgersi sensu lato from Barbuda is 50% greater than in most other fiddler crabs (Gibbs 1974), which suggests that reproduction in land-locked lagoons and dry estuaries on Caribbean islands is autochthonous with limited larval dispersal, i.e., breeding and development take place locally. Our observation (Fig. 7) that the vulva of female M. burgersi sensu stricto is slightly larger than that of M. panema supports the notion of autochthonous development in the Caribbean. The smaller ova and larger clutch sizes in M. panema suggest that the species uses a long-distance dispersal strategy (Gray 1942; Reiger 1998). Similar strategies are found in other semiterrestrial thoracotreme crabs living in xeric habitats (Thurman 1985; Schubart et al. 1998). With populations along the Atlantic coast of South America disconnected reproductively from those in the Caribbean (Thurman et al. 2021), genetic divergence without morphological distinction must have evolved quickly (i.e., 3–4 Mya). Traditionally, we rely on natural selection by environmental conditions or genetic drift in small groups to explain significant alterations in allelic frequencies among the populations of a species (Levins 1968). Since larval distribution throughout populations of M. panema among coastal colonies is mostly likely random, the inter-populational genetic variance in South America is expected to be low. In Caribbean populations where gene flow is limited, inter-populational genetic variation would be greater. Further, intra-populational genetic variation also would be low since the frequency of inbreeding is higher. Because of selection and mutation pressures, we anticipate greater allelic variation among populations of M. burgersi sensu lato in the Caribbean than in M. panema in South America. The geological rift between their respective tectonic plates re-enforces this distinction. We have considered environmental factors such as salinity, substratum and temperature that could lead to genetic and phenotypic divergence among the three clades, and now between two species (Thurman et al. 2021). Recently, the “mitonuclear compatibility species concept” was advanced to explain rapid evolution at the molecular level (Hill 2016). Co-evolution can lead rapidly to divergences in coadapted mitochondrial and nuclear gene sets whenever gene flow among populations is disrupted. Mitochondrial gene products often interact with nuclear mRNAs and proteins. A change in the mitogenomic code may disrupt general cellular function (Hill 2017) and such a mutation could exert selective pressure on the nuclear genome to maintain proper metabolic function. With mutations accumulating rapidly in both the mitochondrial and nuclear genomes, isolated populations would drift apart genetically. Eventually, the mitogenome of one population could become incompatible with the nuclear genes of a different population, leading to reproductive isolation (Callier 2019). Since mitochondria are inherited through the maternal lineage, some paternal nucleogenes may be unresponsive to epistatic mitogenomic regulation, driving sympatric genetic divergence. Although this mechanism is speculative, it is attractive and awaits future investigation in fiddler crabs. Taxonomic distinction among local Minuca species Species in the genus Minuca are often sympatric and difficult to distinguish. M. panema is sympatric with M. mordax (Smith, 1870) (see von Hagen 1983 1984) (Fig. 9A), M. rapax (Smith, 1870) (Fig. 9B), M. victoriana von Hagen, 1987 (Fig. 9C) and M. vocator (Herbst, 1804) (Fig. 9D). Coelho and Coelho-Filho (1993: p. 47–48) published an early identification key for these species. More recently, Masunari et al. (2020) produced an illustrated identification key. Here we provide descriptions and images of other sympatric Minuca for practical comparisons with M. panema. Minuca mordax (Smith, 1870) (Fig. 10). Front angle from midline to lateral margin about 14°. Eyebrows (Fig. 10A: a) visible. Carapace finely tuberculated and pitted. Carapace length 65% of width. H-depression shallow with sparse pubescence in lateral sulci. Frontal region > 34.5% carapace width. Postorbital sulcus (Fig. 10B: b) short and not connect to H-depression. Lower orbital margin (Fig. 10F: c) without tubercles (mostly setae). Anterolateral angles sharp (Fig. 10A: d; Fig. 10 B: d), pointed forward or inward. Hepatic region near anterolateral surface with larger tubercles in a cluster. Transition from anteroto posterolateral lines (Fig. 10B: e) smoothly curving. Posterolateral striae (Fig. 10B: f) long. Dorsal cheliped surface with ridge. External surface with large tubercles. Ventral surface smooth without manuspollex ridge. Dactyl articulation joint (Fig. 10C: h) without row of tubercles. Gap wide. Pollex (Fig. 10C: j) with one central large tubercle, distal end with three tubercles. On inner surface of claw, carina (Fig. 10D: l) on dorsal edge of carpal cavity extending toward dactyl. Prominent knob of large tubercles (Fig. 10D: m) at proximal end of oblique ridge. Distal end of oblique ridge inconspicuous. Area between carpal carina and page 16 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan oblique ridge with large tubercles. Predactyl ridge (Fig. 10D: n) in palm with low, smooth tubercles not easily visible. Very short row of tubercles on dactyl articulation (Fig. 10D: o). Dactyl (Fig. 10C: k) with moderate-sized tubercles in gap but no large “tooth”. Carpus and manus of ambulatory legs 1–3 covered with pubescence and long setae (Fig. 10E: q, r). Pubescence on dorsal, lateral and ventral merus and manus surfaces (Fig. 10E). Width of merus from ambulatory legs 1–3 on minor side approximately 30% of length. Ventral surface of ambulatory legs 1–3, fine pubescence (Fig. 10E). G1 in Crane (1975: p. 381, fig. 67F). Female with small tubercle on operculum of vulva. Minuca rapax (Smith, 1870) (Fig. 11). Angle of front from midline to lateral margin about 14°. Eyebrows (Fig. 11A: a) visible. Carapace surface rough appearing with small tubercles but no pits. Carapace length 63% of width. H-depression very shallow. Frontal region 32.5% carapace width (n = 10). Post-orbital depression (Fig. 11A: b) shallow, no tubercles but shows a channel to H-depression. Margin of lower orbital lined with prominent rectangular dentals (Fig. 11F: c). Two small teeth along lateral edge of orbit. Anterolateral angles (Fig. 11B: d) pointed inward slightly. Intersection of anterolateral and posterolateral (Fig. 11B: e) lines forming smooth curve. Upper posterolateral striae (Fig. 11B: f) long. Second striae, just above ventral carapace margin, shorter (Fig. 11B: f). Major cheliped with ridge on dorsal surface. Tubercles on outer face decreasing in size to ventral manus. Manus with ventral keel (Fig. 11C: p) extending to pollex. Pollex (Fig. 11: j) with midlength large tubercle and terminus with 3–4 tubercles. Dactyl (Fig. 11C: k) with 3–4 larger tubercles proximal to articulation. Gap wide. Inner surface of cheliped with carpal carina (Fig. 11D: l) terminating abruptly in palm. Predactyl ridge (Fig. 11D: n) parallel to row of tubercles on dactyl articulating joint (Fig. 11D: o) (clearly not curved toward palm and carpal cavity). Oblique ridge simple line of tubercles running from lower carpal cavity to ventral edge of manus. Proximal apex (Fig. 11D: m) not prominent. On ambulatory legs, dorsal and lateral surfaces with pubescence and long setae (Fig. Fig. 9. Other sympatric Minuca from the south Atlantic coast of South America. A: Minuca mordax (Smith, 1870), B: Minuca rapax (Smith, 1870), C: Minuca victoriana von Hagen, 1987. D: Minuca vocator (Herbst, 1804). Adult males, scale bar ≈ 10 mm. Specimens not catalogued. page 17 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan 11E: q, r). Ventral surface no pubescence or long setae. Merus width on ambulatory legs 1–3, 37% length (Fig. 11E). G1 in Crane (1975: p. 381, fig. 67C). Female vulvar operculum with large tubercle. See Crane (1975: p. 371, fig. 54F). Minuca victoriana (von Hagen, 1987) (Fig. 12). Front angle from midline to lateral margin about 20°. Eyebrow (Fig. 12A: a) visible. Surface of carapace smooth, shiny and finely granular. Carapace length 59% of width. H-depression deep with pubescence in lateral Fig. 10. Minuca mordax (Smith, 1870), collected from Belize (UNI 47). A: Dorsal view of entire crab. B: Lateral carapace view on side of minor cheliped. C: Outer surface of major cheliped. D: Inner surface of major cheliped. E: Second ambulatory leg. F: Oral view of carapace. a. eyebrow, b. postorbital sulcus, c. suborbital margin, d. anterolateral angle, e. posterolateral line, f. posterolateral striae, h. articulation ridge, j. pollex, k. dactyl, l. superior carpal cavity carina, m. apex of oblique ridge, n. pre-dactyl ridge, o. articulation ridge, q. pubescence, r. setae. page 18 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan sulcus. Frontal region 33% carapace width (n = 10). Post-orbital sulcus shallow (Fig. 12A: b). Ventral margin of orbit with rectangular dentals (Fig. 12F: c). Carapace surface irregular near anterolateral margin (Fig. 12: d, e). Anterolateral angles (Fig. 12B: d) pointing outward. Intersection of lateral and posterolateral (Fig. 12B: e) lines forming sharp obtuse angle. Posterolateral striae very long (Fig. 12B: f). On major cheliped, dorsal surface with ridge. Moderate-size tubercles decreasing in size toward ventral manus. Short keel on ventral manus extending to pollex (Fig. 12C: p). A triangular depression (Fig. 12C: i) with pubescence (Fig. 12C: Fig. 11. Minuca rapax (Smith, 1870), collected from Puerto Rico (UNI 421). A: Dorsal view of entire crab. B: Lateral carapace view on side of minor cheliped. C: Outer surface of major cheliped. D: Inner surface of major cheliped. E: Second ambulatory leg. F: Oral view of carapace. a. eyebrow, b. postorbital sulcus, c. dental on suborbital margin, d. anterolateral angle, e. posterolateral line, f. posterolateral striae, h. articulation ridge, j. pollex, k. dactyl, l. superior carpal cavity carina, m. apex of oblique ridge, n. pre-dactyl ridge, o. articulation ridge, p. manus-pollex ridge, q. pubescence, r. setae. page 19 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan g) just dorsal to origin of pollex (Fig. 12C: j). Dactyl articulation (Fig. 12C: h) without tubercles. Pollex (Fig. 12C: j) with one large tubercle in gap. Gap wide. Dactyl (Fig. 12C: k) with several larger tubercles proximal to articulation in gap with a single large distal tubercle. On inner surface, dorsal carina (Fig. 12D: l) of carpal cavity with elongate tubercles. Carina extends around distal cavity margin to prominent tubercles at proximal end of oblique ridge (Fig. 12D: m). Structure sharply defined with clearly separate tubercles. Predactyl tubercle ridge Fig. 12. Minuca victoriana (von Hagen, 1987), collected from Vitória, Brazil (UNI 168). A: Dorsal view of entire crab. B: Lateral carapace view on side of minor cheliped. C: Outer surface of major cheliped. D: Inner surface of major cheliped. E: Second ambulatory leg. F: Oral view of carapace. a. eyebrow, b. postorbital sulcus, c. dental on suborbital margin, d. anterolateral angle, e. posterolateral line, f. posterolateral striae, g. pubescence, h. articulation ridge, i. pre-pollex depression, j. pollex, k. dactyl, l. superior carpal cavity carina, m. apex of oblique ridge, n. pre-dactyl ridge, o. articulation ridge, p. manus-pollex ridge, q. pubescence, r. setae. page 20 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan parallel to dactyl articulation (Fig. 12D: n, o). Tubercles on dactyl articulation fused. Dorsal surface of carpus in cavity with no large teeth. On ambulatory legs (1–3), dorsal manus and carpus with pubescence and long setae (Fig. 12E: q, r). No setae or pubescence on ventral merus of ambulatory legs. Merus width of ambulatory legs 1–3 about 29% length (Fig. 12E). G1 illustrated in von Hagen (1987: p. 86, fig. 3A–C). Female vulvar operculum flat, without tubercle. Minuca vocator (Herbst, 1804) (Fig. 13). Front Fig. 13. Minuca vocator (Herbst, 1804), collected from Curaçao (UNI 713). A: Dorsal view of entire crab. B: Lateral carapace view on side of minor cheliped. C: Outer surface of major cheliped. D: Inner surface of major cheliped. E: Second ambulatory leg. F: Oral view of carapace. a. eyebrow, b. postorbital sulcus, c. dental on suborbital margin, d. anterolateral angle, e. posterolateral line, f. posterolateral striae, g. pubescence, h. articulation ridge, i. pre-pollex depression, j. pollex, k. dactyl, l. superior carpal cavity carina, m. apex of oblique ridge, n. pre-dactyl ridge, o. articulation ridge, p. manus-pollex ridge, q. pubescence, r. setae. page 21 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan angled from midline to lateral margin about 16°. Eyebrow visible (13A: a). Carapace length 68% of width. Dorsal surface of central carapace smooth with pubescence on lateral hepatic regions (Fig. 13A: g). H-depression shallow with pubescence. Frontal region 37% carapace width (n = 10). Post-orbital sulcus shallow (Fig. 13A: b). Lower orbital margin without rectangular dentations (Fig. 13F: c). Anterolateral angles (Fig. 13B: d) pointed inward. Anterolateral lines curved. Junction with posterolateral (Fig. 13B: e) line forming curve. Dorsolateral lines with pubescence in sulcus (Fig. 13B: d, e). Posterolateral striae (Fig. 13B: f) heavily pubescent. Pubescence between striae and ventral margin of carapace (13B: g). Dorsal ridge on male cheliped almost flat. Tubercles on outer face small, visible only with magnification. Ventral manus with prominent keel (Fig. 13C: p) extend to pollex. Predactyl ridge (Fig. 13C: h) smooth. No tubercles on dactyl articulation. Base of pollex with shallow oblong depression (Fig. 13C: i). Pollex (Fig. 13: j) smooth. Gap wide. Few tubercles in gap, largest at mid-length. Pollex (Fig. 13C: j) terminus with three tubercles. Dactyl smooth, few larger “teeth” at proximal end (Fig. 13C: k). Inner face of cheliped with a prominent knob of tubercles (Fig. 13D: m) protruding into carpal cavity. Carina of superior carpal cavity formed from fused tubercles (Fig. 13D: l). Carina ends in patch of larger tubercles extending to predactyl ridge (Fig. 13D: n). Predactyl ridge with large, widely-space tubercles. Few tubercles on dactyl articulation (Fig. 13D: o). Lower palm smooth. A cluster of 5–8 large tubercles (Fig. 13D: m) on lower edge of carpal cavity. Oblique ridge poorly developed. Large smooth sulcus (Fig. 13D: i) between oblique ridge and predactyl ridge. Heavy pubescence (Fig. 13E: q) on dorsal and ventral surfaces on ambulatory legs 1–3, but none on lateral surface of manus and carpus. Merus width of third ambulatory legs about 40% of length (Fig. 12E). Dorsal surface of merus with heavy pubescence (Fig. 12E: q). Ventral surface of merus without pubescence or setae. G1 in Crane (1975: p. 380, fig. 66D). Female with extremely large tubercle on vulvar operculum. CONCLUSIONS We describe a species of fiddler crab related to M. burgersi sensu stricto. Three closely related clades in the M. burgersi species complex occur across its range in the western Atlantic Ocean. The southern-most clade (“Clade 1” in Thurman et al. 2021) was considered to be M. burgersi sensu stricto. Specimens from this clade collected along the Atlantic coast of South America between the Island of Trinidad and Santa Catarina, Brazil are now recognized as Minuca panema (Coelho, 1972). We offer molecular and morphological evidence to distinguish the species from M. burgersi sensu stricto. Based on a molecular clock, the “burgersi-aff. burgersipanema” complex diverged from a common ancestor 4.1 Mya as a result of changing geology and hydrology along the coast of northeastern South America. Acknowledgments: Portions of this research were supported by the Dr. Gary and Myrna Floyd Undergraduate Research Assistantship Fund (UNI). A Fulbright Fellowship and the University of Iowa Global Regional Environmental Research Center (GRERCSA #1000716062, G/P #1802010001) supported CLT during studies in Brazil during 2009 and 2010. Collecting expenses incurred by CLT in Barbados, Curaçao, Trinidad and Guyana were deferred in part by a gift from Emily Van Laar to the UNI Department of Biology Undergraduate Research Fund. Cultural Insurance Service International (CISI) travel protection (for CLT) was provided by the UNI Study Abroad Center and the UNI Department of Biology. JCM received funding from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP #2007/04870-9, #2009/50799-0), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq #300662/2009-2, #450320/20103) and the Coordenadoria de Aperfeiçoamento de Pessoal de Ensino Superior (CAPES, #33002029031P8 Financiamento 001). This study was supported by grants to HTS (MOST 111-2621-B-005-003; NSTC 112-2313-B-005-051-MY3) from the Ministry of Science and Technology, Executive Yuan, Taiwan. Paula Carvalho de Castro, UNI Geography Department, provided cartography. Access to museum specimens was enabled by Rafael Lemaitre and Karen J. Reed (USNMWashington, D.C.), Karen van Dorp (RMNH-Leiden) and Marcos Tavares (ZMUSP-São Paulo). We greatly appreciate the search by Jesser Fidelis de Souza Filho (MOUFPEPernambuco) for the original holotype and paratypes of U. panema. The help provided by Marcos Tavares, Joana d’Arc de Jesus Pinto and Maria Jose de Souza Coelho locating ZMUSP specimens is greatly appreciated. Specimens for this research were collected under scientific permits issued by the following authorities. Bahamas: Department of Fisheries, Ministry of Agriculture, Fisheries and Local Government (Nassau), permit MAF/FIS/17. Puerto Rico: Departmento de Recursos Naturales y Ambientales (San Juan) permit 2008-IC-003 & US Fish and Wildlife Service, Caribbean Islands National Wildlife Refuge (Cabo Rojo), permit 41521-090005. US Virgin Islands: Department of Planning and Natural Resources, Division of Fish and Wildlife (St. Thomas), permit page 22 of 26Zoological Studies 62:45 (2023) © 2023 Academia Sinica, Taiwan STT-032-07 & US Department of the Interior National Park Service (St. John) permit VIIS-2007SCI-0010. Barbados: Ministry of Environment and Drainage (St. Michael) permit 8434/56/1 vol. iii. Curaçao: CARMABI Foundation (Piscaderabaa), permit 2012/48584. Trinidad and Tobago: Wildlife Section, Forestry Division (St. Joseph) permit Feb. 19, 2018. Guyana: Environmental Protection Agency and University of Guyana Biodiversity Center (Georgetown) permit 070618 BR010. Brazil: Ministério do Meio Ambiente/Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis/Instituto Chico Mendes de Conservação da Biodiversidade (MMA/IBAMA/ ICMBio) permit #10BR004543/DF to CLT and permits #18559-1, #23976-1, #29594-1 and #29594-3 to JCM. In addition, we wish to thank: Dr. Samuel Faria (CEBIMar/USP for facilitating collecting in Brazil; Dr. Julia Horrocks (University of West Indies-Cave Hill) for assistance on Barbados; Drs. M. J. A. Vermeij and Paul G. C. Stokkermans (CARMABI-Piscaderabaai) for support on Curaçao; Chad Thurman and Dr. Judith Gobin, Aaron Peter, and the late Aaron Kalloo (University West Indies-San Augustine) for help on Trinidad; Dr. Elford Liverpool and Michael Philander (The Biodiversity Institute at the University of Guyana – Georgetown) for guidance in Guyana. We also appreciate the contributions of Reid Alber (UNI) and Dr. Melanie Hopkins (AMNH) during the morphometric studies. We are indebted to the late Dr. Christoph Schubart and an anonymous reviewer whose comments greatly improved the manuscript. Authors’ contributions: CLT and JCM conceived this study, collected and processed the samples and drafted the manuscript. HTS performed the molecular analysis and edited the manuscript. All authors read and approved the final manuscript. Competing interests: The authors declare that they have no conflicts of interests. Availability of data and materials: For accessibility, museum specimen numbers are presented in the text and tables. DNA sequences generated in the study have been deposited into GenBank. (Accession numbers are provided in Table 1). Consent for publication: Not applicable. Ethics approval consent to participate: Not applicable. REFERENCES Almeida AO de, Coelho PA. 2008. Estuarine and marine brachyuran crabs (Crustácea: Decapoda) from Bahía, Brazil: checklist and zoogeographical considerations. 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