Sciadicleithrum spp. (Dactylogyridae, Monopisthocotyla) parasitizing Saxatilia brasiliensis (Cichlidae, Cichliformes) from the Munim River Basin, northeastern Brazil, with a description of a new species

Sciadicleithrum spp. (Dactylogyridae, Monopisthocotyla) parasitizing Saxatilia brasiliensis (Cichlidae, Cichliformes) from the Munim River Basin, northeastern Brazil, with a description of a new species Marciara L. Silva1,2,3,4, Felipe P. Ottoni2, Diego C. Viana5, Dennisiane J. Saraiva1,3, Marcia Cristina N. Justo1, Simone C. Cohen1 1 Laboratório de Helmintos Parasitos de Peixes, Instituto Oswaldo Cruz, FIOCRUZ. Avenida Brasil 4365, 21040-360 Rio de Janeiro, RJ, Brazil 2 Laboratório de Sistemática e Ecologia de Organismos Aquáticos, Universidade Federal do Maranhão (UFMA), Campus de Chapadinha, BR-222, KM 04, S/N, Chapadinha, MA, Brazil 3 Programa de Pós Graduação em Biodiversidade e Saúde, Instituto Oswaldo Cruz, FIOCRUZ, Avenida Brasil 4365, 21040-360, Rio de Janeiro, RJ, Brazil 4 Programa de Pós-Graduação em Ciência Animal, Universidade Estadual do Maranhao (UEMA), Cidade Universitaria Paulo VI, Avenida Lourenco Vieira da Silva 1000, 65055-310 Sao Luis, MA, Brazil 5 NúcleodeEstudosMorfofisiológicosAvançados,UniversidadeEstadualdaRegiãoTocantinadoMaranhão.CampusImperatriz,Rua Godofredo Viana 1300, 65901-480 Imperatriz, MA, Brazil https://zoobank.org/CB39D6B4-6664-45D8-950F-736CDEDDCAAF Corresponding author: Marcia Cristina N. Justo (mar[email protected]) Academic editor: Tom Artois ♦ Received 21 January 2025 ♦ Accepted 31 March 2025 ♦ Published 13 November 2025 Abstract During a study conducted on the helminth fauna of fishes in the middle Munim River Basin, Maranhão State, northeastern Brazil, a new species of Sciadicleithrum, S. anapurusensis sp. nov., is reported from the gills of Saxatilia brasiliensis (Bloch, 1792), a cichlid endemic to the Northeast region of Brazil. In addition, a known species, Sciadicleithrum araguariensis Paschoal, Scholz, Tavares-Dias & Luque, 2016, was recovered from the same host and is redescribed here, providing new morphological and biogeographical data. Sciadicleithrum anapurusensis sp. nov. differs from all congeneric species in the general morphology of sclerotized structures (anchors, bars, vagina, accessory piece, and the number of MCO rings), being mainly characterized by the bifurcated accessory piece with unequal branches at the distal portion, with a subterminal thin projection and a hook-shaped terminal end. The findings of this study emphasize the importance of carrying out comparable surveys on different host species in order to increase the knowledge on monopisthocotylan parasites of fishes in this area. Furthermore, the finding of two congeneric species in the same host species reinforces the host specificity of Sciadicleithrum species to cichlid hosts. Key Words Cichlinae, Crenicichlina, hosts, Maranhão, Saxatilia brasiliensis Introduction Brazil has a significant richness of fish species and plays a fundamental role in discussions about the freshwater ecosystem, as well as its biodiversity and conservation (Azevedo-Santos et al. 2021). Nevertheless, like the rest of the planet, due to the exponential increase in anthropogenic impacts on ecosystems and the high extinction rates of species and populations, leading to a rapid loss of biodiversity, we are facing a serious global phenomenon, known as the “Biodiversity Crisis”, which is rapidly leading our planet towards a mass extinction (Savage 1995; Brooks et al. 2002; Singh 2002; Brook et al. 2006; Pimm et al. 2014; Ceballos et al. 2015; Hogue and Breon 2022). This global crisis is more serious in freshwater ecosystems, which are more vulnerable to anthropogenic Zoosyst. Evol. 101 (4) 2025, 2161–2169|DOI 10.3897/zse.101.147382 Copyright Silva, M.L. et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. zse.pensoft.net Silva, M.L. et al.: A new species of Sciadicleithrum 2162 impacts and have higher rates of species and population extinctions, as these freshwater ecosystems are being altered, degraded, or destroyed more quickly and sharply, a phenomenon called the “Freshwater Biodiversity Crisis” (Darwall et al. 2018; Harrison et al. 2018; Reid et al. 2019; Albert et al. 2020; Tickner et al. 2020; Ottoni et al. 2023). Therefore, the mitigation of the effects of human actions on freshwater ecosystems and their conservation needs to be a priority (Albert et al. 2020; Tickner et al. 2020; Ottoni et al. 2023). Brazil is facing all the problems and scenarios mentioned above, including the accelerated rate of degradation, fragmentation, and loss of freshwater ecosystems, and consequently, of the related biodiversity (Pereira-Júnior and Pereira 2017; Azevedo-Santos et al. 2023). The Cichlidae comprises the greatest species richness among families of Cichliformes, currently comprising 1762 valid species, among which 564 are included within Cichlinae (Fricke et al. 2025a), a subfamily that naturally occurs exclusively in the Neotropical region (Smith et al. 2008; López-Fernández et al. 2010). Cichlinae is divided into seven tribes: Cichlini, Retroculini, Astronotini, Chaetobranchini, Geophagini, Cichlasomatini, and Heroini; the last three being the most diverse ones (Smith et al. 2008; López-Fernández et al. 2010). However, despite the great fish species richness, especially in the tropics, little is known about the diversity and richness of the parasite fauna from these potential hosts (Avise et al. 2008). Tavares-Dias et al. (2022) estimated that only 6% of monopisthocotylan richness is known, incipient knowledge given the richness of fish species that exists, and that each host species hosts at least two monopisthocotylan species. The proportion of cichlid species worldwide examined for the presence of Monopishtocotyla is low, and the diversity of these helminths parasitizing cichlid fishes in the Neotropical Region remains understudied compared to their counterparts in Africa. However, this imbalance is more likely due to differences in sampling efforts rather than actual variations in species richness among genera (Pariselle et al. 2011). Sciadicleithrum Kritsky, Thatcher & Boeger, 1989 was proposed to accommodate Sciadicleithrum uncinatum Kritsky,Thatcher & Boeger, 1989 parasite from Cichla ocellaris Bloch & Schneider, 1801. To date, 30 species of Sciadicleithrum have been described from different host species, belonging to the family Cichlidae listed in Table 1. The Munim River Basin is mainly located at the Cerrado Biome of the Maranhão State; however, its lower portion is located in a region between the Cerrado and Amazon biomes, and its mouth is at the Bay of São José, in a region known as the “Golfão Maranhense” (Vieira et al. 2023). A recent fish inventory, conducted by Vieira et al. (2023), revealed the existence of 123 fish species in this river system, considerably increasing its known fish diversity, which was underestimated until the publication of the inventory. During studies with Saxatilia brasiliensis (Bloch, 1792), a cichlid endemic to the Northeastern region of Brazil (Fricke et al. 2025b; Froese and Pauly 2024) in the Munim River Basin in Maranhão state, a new species and a previously known species, both Sciadicleithrum, were identified. This new species of Sciadicleithrum is not morphologically similar to those previously known. In the present study, the species are described and redescribed, respectively, based on morphological features. These results expand the knowledge of the biodiversity of the fish parasites of the region. Materials and methods Specimens of Saxatilia brasiliensis were collected in two tributaries of the Munim River Basin, named Stream Feio (03°51'18.1"S, 043°17'14.0"W) (S1) at the rural zone of the Municipality of Chapadinha and Stream Estrela (03°40'15.6"S, 043°7'9.7"W) (S2) in the Municipality of Anapurus, both located in the Maranhão State, Northeastern region of Brazil (Fig. 1). Figure 1. Map with the geographic location of the sample sites: S1— Stream Feio in São José Village, in the Municipality of Chapadinha, and S2—Stream Estrela, Balneary of Anapurus, in the Municipality of Anapurus, Munim River Basin, Maranhão State, Brazil. Zoosyst. Evol. 101 (4) 2025, 2161–2169 zse.pensoft.net 2163 Table 1. Checklist of Sciadicleithrum species parasites of cichlid fishes from the Neotropical Region. MonopisthocotylaHost Countries References Sciadicleithrum amazoniensis Morey, Dávila, Arimuya, Sousa, Cruces & Chero, 2024 Biotodoma cupido (Heckel, 1840) Peru Morey et al. (2024) Sciadicleithrum aequidens (Price and Schlueter, 1967) Kritsky, Thatcher & Boeger, 1989 Cleithracara maronii (Steindachner, 1881) Guiana Kritsky et al. (1989) Sciadicleithrum araguariensis Paschoal, Scholz, Tavares-Dias & Luque, 2016 Saxatilia labrina (Spix & Agassiz, 1831) Brazil Paschoal et al. (2016) Sciadicleithrum bravohollisae Kritsky, Vidal-Martinez & Rodriguez-Canul, 1994 Cincelichthys pearsei (Hubbs, 1936) Mexico Kritsky et al. (1994) Sciadicleithrum cavanaughi (Price, 1966) Kritsky, Thatcher & Boeger, 1989 Cleithracara maronii (Steindachner, 1881) Guiana Kritsky et al. (1989) Sciadicleithrum bicuense Vidal-Martínez, Scholz & Agulrre-Macedo, 2001 Amatitlania nigrofasciata (Günther, 1867) Nicaragua Vidal-Martínez et al. (2001) Sciadicleithrum edgari Paschoal, Scholz, Tavares-Dias & Luque, 2016 Satanoperca jurupari (Heckel, 1840) Brazil Paschoal et al. (2016) Sciadicleithrum ergensi Kritsky, Thatcher & Boeger, 1989 Cichla ocellaris (Bloch & Schneider, 1801) Brazil Kritsky et al. (1989) Sciadicleithrum feliciajaramae Morey, Dávila, Arimuya, Sousa, Cruces & Chero, 2024 Bujurquina peregrinabunda Kullander, 1986 Peru Morey et al. (2024) Sciadicleithrum frequens Bellay, Takemoto, Yamada & Pavanelli, 2008 Geophagus brasiliensis (Quoy & Gaimard, 1824) Brazil Bellay et al. (2008) Sdadicleithrum geophagi Kritsky, Thatcher & Boeger, 1989 Geophagus surinamensis (Bloch, 1791) Brazil Kritsky et al. (1989) Sciadicleithrum guanduensis Carvalho, Tavares & Luque, 2008 Geophagus brasiliensis (Quoy & Gaimard, 1824) Brazil Carvalho et al. (2008) Sciadicleithrum iphthimum Kritsky, Thatcher & Boeger, 1989 Pterophyllum scalare (Lichtenstein, 1823) Brazil Kritsky et al. (1989) Sciadicleithrum joanae Yamada, Takemoto, Bellay & Pavanelli, 2009 Crenicichla niederleinii (Holmberg, 1891) Brazil Yamada et al. (2009) Sciadicleithrum juruparii Melo, Santos & Santos, 2012 Satanoperca jurupari (Heckel, 1840) Brazil Melo et al. (2012) Sciadicleithrum kritskyi Bellay, Takemoto, Yamada & Pavanelli, 2009 Geophagus proximus (Castelnau, 1855) Brazil Bellay et al. 2009 Sciadicleithrum maculicaudae Vidal-Martínez, Scholz & Agulrre-Macedo, 2001 Vieja maculicauda (Regan, 1905) Nicaragua Vidal-Martínez et al. (2001) Sciadicleithrum meekii Mendoza-Franco, Scholz & Vidal-Marstínez, 1997 Thorichthys meeki Brind, 1918 Mexico Mendoza-Franco et al. (1997) Sciadicleithrum mexicanum Kritsky, Vidal-Martinez & Rodriguez-Canul, 1994 Mayaheros urophthalmus (Günther, 1862) Mexico Kritsky et al. (1994) Sciadicleithrum nicaraguense Vidal-Martínez, Scholz & Agulrre-Macedo, 2001 Cribroheros alfari (Meek, 1907) Nicaragua Vidal-Martínez et al. (2001) Sciadicleithrum panamensis Mendoza-Franco, Aguirre-Macedo, & Vidal-Martínez, 2007 Andinoacara coeruleopunctatus (Kner 1863) Panama Mendoza-Franco et al. (2007) Sciadicleithrum paranaenses Bellay, Takemoto, Yamada & Pavanelli, 2009 Geophagus proximus (Castelnau, 1855) Brazil Bellay et al. (2009) Sciadicleithrum satanopercae Yamada, Takemoto, Bellay & Pavanelli, 2009 Satanoperca pappaterra (Heckel, 1840) Brazil Yamada et al. (2009) Sciadicleithrum souzatecci Morey, Dávila, Arimuya, Sousa, Cruces & Chero, 2024 Bujurquina peregrinabunda Kullander, 1986 Peru Morey et al. (2024) Sciadicleithrum splendidae Kritsky, Vidal-Martinez & Rodriguez-Canul, 1994 Petenia splendida Günther, 1862 Mexico Kritsky et al. (1994) Sciadicleithrum tortrix Kritsky, Thatcher & Boeger, 1989 Uaru amphiacanthoides Heckel, 1840 Brazil Kritsky et al. (1989) Sciadicleithrum umbilicum Kritsky, Thatcher & Boeger, 1989 Cichla ocellaris Bloch & Schneider, 1801 Brazil Kritsky et al. (1989) Sciadicleithrum uncinatum Kritsky, Thatcher & Boeger, 1989 Cichla ocellaris Bloch & Schneider, 1801 Brazil Kritsky et al. (1989) Sciadicleithrum variabilum (Mizelle & Kritsky, 1969) Kritsky, Thatcher & Boeger, 1989 Symphysodon discus Heckel, 1840 Brazil Kritsky et al. (1989) Fishes were collected using nets 240 cm long and 100 cm high. A total of sixty-four specimens of S. brasiliensis were obtained, 32 from each locality (sixteen specimens were collected in the dry season and sixteen in the rainy season). The collections were authorized by the “Sistema de Autorização e Informação em Biodiversidade (SISBIO)” under the number 6441-5, while the laboratory procedures were licensed by the “Comitê de Ética em Experimentação Animal (CEA)” from the Estadual University of Maranhão, under the protocol 11/202101200.002200/2015-06. The fishes were taken to the "Laboratório de Sistematica e Ecologia de Organismos Aquáticos", Federal University of Maranhão (UFMA), where fish euthanasia, preservation and identification were carried out by the laboratory team. The fishes were deposited at the "Coleção Ictiológica do Centro de Ciências Agrárias e Ambientais (CICCAA)" of the Universidade Federal do Maranhão under voucher numbers CICCAA07121 - CICCAA07151. At the laboratory, the branchial arches were removed and placed in vials containing hot water (~65 °C) for relaxing and detaching of Monopisthocotyla, and then the vials were vigorously shaken. After cooling, absolute ethanol was added to reach the concentration of 70%. The content (liquid and branchial arches) was analyzed under a stereoscopic microscope for collection of the parasites. For morphological studies of sclerotized parts (copulatory complex and haptoral sclerites), parasites were mounted in Hoyer’s medium (Humason, 1979). The material was sent to "Laboratório de Helmintos Parasitos de Peixes, Instituto Oswaldo Cruz, FIOCRUZ", Rio de Janeiro State, Brazil, to be characterized and identified. Specimens of Sciadicleithrum araguariensis Paschoal, Scholz, Tavares-Dias & Luque, 2016 (Holotype CHIOC no. 38091a; paratypes CHIOC no. 38091b, c, d) were examined for comparative purposes. Drawings were taken using a Zeiss® Axioskop microscope micrographic system with a differential interference contrast (DIC) apparatus and an Olympus zse.pensoft.net Silva, M.L. et al.: A new species of Sciadicleithrum 2164 BX 41 microscope with phase contrast, equipped with a camera lucida. Measurements are presented in micrometers; means are followed by range and number of structures measured (n) in parenthesis; lengths of curved or bent structures represent the straight-line distances between extreme ends, except for the copulatory complex, measured using IMAGEJ software (Wayne 2010), distributed by the National Institutes of Health (NIH), and available at https://imagej.nih.gov/ij/download.html. Distribution of hooks followed Mizelle and Price (1963). The studied specimens were deposited in the "Coleção Helmintológi ca do Instituto Oswaldo Cruz (CHIOC)", Rio de Janeiro, Brazil. Results Phylum Platyhelminthes Gegenbaur, 1859 Class Monopisthocotyla Brabec, Salomaki, Kolısko, Scholz & Kuchta, 2023 Order Dactylogyridea Bychowsky, 1937 Dactylogyridae Bychowsky, 1933 Sciadicleithrum Kritsky, Thatcher & Boeger, 1989 Sciadicleithrum anapurusensis sp. nov. https://zoobank.org/018120EB-D65E-494C-B4FE-45316CA0D1CA Fig. 2 Host. Saxatilia brasiliensis (Bloch, 1792) (Cichlidae, Cichliformes) Type-locality. Stream Estrela, balneary of Anapurus, urban zone of the municipality of Anapurus, Munim River Basin, Maranhão State, Brazil (03°40'15.6"S, 043°7'9.7"W). Other localities. Stream Feio, San José village, rural zone of the municipality of Chapadinha, Munim River Basin, Maranhão State, Brazil (03°51'18.1"S, 043°17'14.0"W) Etymology. The epithet specific refers to the host’s location, the municipality of Anapurus, Maranhão State, Brazil. Specimens deposited. Holotype (CHIOC 40480), Paratypes (CHIOC: 40481a, b; 40482; 40483; 40484; 40485; 40486a, b; 40487) Number of examined hosts. 64. Number of parasites. 274. Prevalence. 64.1%. Range of intensity. 1–27 parasites per fish. Mean intensity. 6.7 parasites per infected fish. Mean abundance. 4.3 parasites per analyzed fish. Description. (Based on 27 specimens mounted in Hoyer’s medium): Body elongated, fusiform, 363 (256–470, n = 27) long, including haptor, by 138 (108–195, n = 27) wide at level of ovary; tegument smooth; three developed cephalic lobes, two lateral and one terminal; four pairs of head organs; cephalic glands indistinct; accessory granules sparse in cephalic area; four equidistant eyespots, eye granules elongate ovate. Pharynx 32 (28–38, n = 5) in diameter; esophagus short; caeca confluent posterior to testis, without diverticula (Fig. 2A). Copulatory complex comprises male copulatory organ (MCO) and accessory piece. MCO 111 (92–123, n = 16) long and 18 (15–22, n = 15) wide, composed of 2 clockwise rings; accessory piece 40 (27–50, n = 22) long, 12 (10–14, n = 19) wide, non-articulated to MCO base, bifurcated, with unequal branches at distal portion, the longest widens to distal region, with a subterminal thin projection and terminal end hook-shaped (Fig. 2B). Gonads slightly overlapping. Testis dorsal to germarium; vas deferens looping left intestinal cecum; seminal vesicle elongated and single rounded prostatic reservoir. Germarium pretesticular; seminal receptacle, Mehlis’ glands, ootype, eggs, and uterus not observed (Fig. 2A). Vagina weakly sclerotized, opening ventrally, forming a bulb near the aperture, vaginal canal long, thin (Fig. 2C). Vitellaria distributed throughout the trunk (Fig. 2A). Peduncle broad; haptor subhexagonal 97 (75–133, n = 25) wide. Ventral anchor 17 (13–20, n = 26) long, straight, with short deep root, superficial root developed presenting a little hump between the superficial and deep roots, base 14 (11–16, n = 26) wide (Fig. 2D); dorsal anchor 31 (23–37, n = 27), long, with differentiated roots, well-developed superficial root, and short and developed deep root, base 19 (14–22, n = 24) (Fig. 2E). Ventral bar 27 (22–35, n = 26) long, yoke-shaped, with enlarged extremities and delicate postero-medial umbiliform membrane (Fig. 2F, G); dorsal bar 19 (15–22, n = 25) long, straight, with extremities directed posteriorly (Fig. 2H). Hook pairs similar in shape and dissimilar in size, pairs 1 and 5 slightly smaller: Pair 1, 11 (11–12, n = 10); pair 2, 12 (12–13, n = 10); pair 3, 13 (12–13, n = 10); pair 4, 13 (13, n = 10); pair 5, 11 (10–12, n = 9); pair 6, 13 (12–13, n = 9); pair 7, 12 (12–13, n = 9) with Ancyrocephalinae distribution, straight shank with protuberant thumb, recurved shaft, point; FH loop about ¾ shaft length. Remarks. Sciadicleithrum anapurusensis sp. nov. was allocated in Sciadicleithrum by the diagnostic characters of the genus, such as the male copulatory organ that consists of a spiral tube comprising one to several clockwise rings, gonads overlapping, testis dorsal to ovary, and hooks of similar shape and size and not dilated shank (Kritsky et al. 1989). Species of the genus were characterized as presenting two variably developed umbeliform membranes on the anterior bar margin, but this character is no longer considered differential, as some species that do not exhibit these characteristics were included in the genus. The new species differs from all congeneric species in the general morphology of the sclerotized structures (anchors, bars, vagina, accessory piece, and the number of MCO rings). The new species is closely related to Sciadicleithrum satanopercae Yamada, Takemoto, Bellay & Pavanelli, 2009, Sciadicleithrum araguariensis Paschoal, Tavares-Dias, Scholz & Luque, 2016, Sciadicleithrum edgari Paschoal, Tavares-Dias, Scholz & Luque, 2016, and Sciadicleithrum amazoniensis Morey, Dávila, Arimuya, Sousa, Cruces & Chero, 2024 by the bifurcated accessory piece, but differs by the presence of postero-medial umbiliform membranes in the ventral bar. Zoosyst. Evol. 101 (4) 2025, 2161–2169 zse.pensoft.net 2165 Sciadicleithrum araguariensis Paschoal, Scholz, Tavares-Dias & Luque, 2016 Fig. 3 Type host and locality. Saxatilia labrina (Spix & Agassiz, 1831) [=Crenicichla labrina (Spix & Agassiz, 1831)] (Cichlidae, Cichliformes), Araguari River in Ferreira Gomes (0°52'N, 51°12'W), Amapá State, Brazil. Other host. Saxatilia brasiliensis (Bloch, 1792) (Cichlidae, Cichliformes) Other localities. Stream Estrela, balneary of Anapurus, urban zone of the municipality of Anapurus, Munim River Basin, Maranhão State (03°40'15.6"S, 043°7'9.7"W); Stream Feio, San José village, rural zone of the municipality of Chapadinha, Munim River Basin, Maranhão State, Brazil (03°51'18.1"S, 043°17'14.0"W). Figure 2. Sciadicleithrum anapurusensis sp. nov. A. Total, ventral; B. Copulatory complex; C. Vagina; D. Ventral anchor; E. Dorsal anchor; F, G. Ventral bar; H. Dorsal bar; I. Hook. Scale bars: 100 µm (A); 20 µm (B, D–H); 40 µm (C); 5 µm (I). zse.pensoft.net Silva, M.L. et al.: A new species of Sciadicleithrum 2166 Specimens deposited. Voucher (CHIOC 40488; 40489; 40490; 40491a-d). Number of examined hosts. 64. Number of parasites. 83. Prevalence. 50%. Range of intensity. 1–6 parasites per fish. Mean intensity. 2.6 parasites per infected fish. Mean abundance. 1.3 parasites per analyzed fish. Redescription. (based on 20 specimens mounted in Hoyer’s medium; original measurements are presented in brackets): Body elongated, fusiform, 342 (250–397, n = 15) [412–430 (419; n = 8)] long, 141 (71–198, n = 17) [95 (90–102; n = 6)], width at the region near vagina; tegument smooth; three cephalic lobes, two lateral and one terminal; four well-developed eye spots, posterior pair larger than anterior; pharynx spherical, 35 (32–41, n = 6) [22 (21–24; n = 4)] in diameter (Fig. 3A). Copulatory complex comprises male copulatory organ (MCO) and accessory piece. MCO tubular, thin, with 1.5 to 2 clockwise rings, 97 (75–110; n = 9) [100 (92–104; n = 4)] long. Accessory piece 29 (21–38; n = 7) [40 (38– 42; n = 5)] long by 12 (8–15; n = 9) wide, non-articulated to the MCO base, formed by a bifurcated tube at mid-region and a slightly sclerotized cap at distal region (Fig. 3B). Vagina strongly sclerotized, vaginal aperture bulbous-shaped, and vaginal canal long (Fig. 3C). Egg 60 (n = 1) in diameter. Haptor 101 (81–128, n = 17) [43 (40–48; n = 8)] wide (Fig. 3A); ventral anchor 18 (15– 22, n = 17) [26 (24–28; n = 7)] long, base 12 (11–16, n = 17) [22 (21–24; n = 7)], superficial root elongated and short deep root, presenting a little hump between the roots, straight shaft and recurved point (Fig. 3D); dorsal anchor 27 (23–30, n = 16) [34 (31–39; n = 7)] long, base, 13 (11–18, n = 16) [32 (30–34; n = 6)] base, slightly elongated superficial root, inconspicuous deep root (Fig. 3E); ventral bar 30 (24–34, n = 20) [31 (29–34; n = 4)] long, yoke-shaped, with expanded ends and delicate umbelliform membrane (Fig. 3F); dorsal bar 22 (18–26, n = 14) [22 (21–25; n = 5)] long, straight, with expanded ends directed posteriorly and postero-medial umbelliform membrane (Fig. 3G). Hooks of similar shape and size: Pair 1, 11 (10–12, n = 12); pair 2, 12 (11–12, n = 12); pair 3, 13 (12–13, n = 12); pair 4, 13 (12–13, n = 11); pair 5, 11 (10–11, n = 6); pair 6, 12 (12–13, n = 9); pair 7, 12 (12–13, n = 11) [14 (12–16; n = 9)] with ancyrocephaline distribution, straight shaft, prominent thumb, recurved point; FH loop about ¾ shaft length (Fig. 3H). Remarks. Sciadicleithrum araguariensis was originally described from specimens of Crenicichla labrina (now recognized as Saxatilia labrina) collected from the Araguari River in Ferreira Gomes, Amapá State, Brazil. The species is now reported in S. brasiliensis from Maranhão State. The specimens analyzed in this study are morphologically similar to those described originally, except for the presence of a cap at the distal portion of the accessory piece. While the original description characterized the accessory piece as Y-shaped and proximally bent, it did not mention the structure observed in the current specimens. Upon re-examining the holotype and paratypes, the cap was observed by the authors of this study. Discussion The parasitofauna associated with the vast majority of Neotropical cichlid hosts remains largely unknown. To date, six genera of dactylogyrids are known to parasitize Neotropical cichlids: Biotodomella Morey, Arimuya & Boeger, 2019 (1 sp.), Gussevia Kohn & Paperna, 1964 (13 spp.), Sciadicleithrum Kritsky, Thatcher & Boeger, 1989 (30 spp.), Trinidactylus Hanek, Molnar & Fernando, 1974, Tucuranella Mendoza-Franco, Scholz & Rozkosná, 2010, and Parasciadicleithrum Mendoza-Palmero, Blasco-Costa, Hernández-Mena & Pérez-Ponce de León, 2017, each with one species described from Brazil, Peru, Venezuela, Mexico, Panama, and Nicaragua. In addition, species of Cichlidogyrus Paperna, 1960, Enterogyrus Paperna, 1963, and Scutogyrus Pariselle & Euzet, 1995, were reported from African introduced hosts, such as Oreochromis spp. (Kritsky et al. 1986, 1989; Bellay et al. 2008, 2009; Carvalho et al. 2008; Yamada et al. 2009; Mendoza-Franco et al. 2010; Melo et al. 2012; Paschoal et al. 2016; Mendoza-Palmero et al. 2017; Morey et al. 2019, 2024; Justo et al. 2020; Seidlová et al. 2022), also in the Neotropical Region. Monopishtocotylans are known to be host specific, with the majority of species parasitizing a single host species. Nevertheless, members of Sciadicleithrum are recognized to parasitize from one to 15 cichlid species, considering that Sciadicleithrum bravohollisae Kristky, Vidal-Martinez & Rodriguez-Canul, 1994 is reported from 15 different host species (Seidlová et al. 2022). Species of Sciadicleithrum were recorded in 18 genera of fish, all from the family Cichlidae. Recently, Varella et al. (2023) conducted a taxonomic review and phylogeny of the subtribe Crenicichlina, the largest clade of the tribe Geophagini, and subfamily Cichlinae, including over 100 species, which previously included only two genera: Crenicichla Heckel, 1840 and Teleocichla Kullander, 1988 (Varella et al. 2023). As a result of that work, the genus Crenicichla was split, resulting in the description of four new genera. Thus, the current composition of the subtribe Crenicichlina includes the following genera: Crenicichla, Teleocichla, Lugubria Varella, Kullander, Menezes, Oliveira & López-Fernández, 2023, Saxatilia Varella, Kullander, Menezes, Oliveira & López-Fernández, 2023, Wallaciia Varella, Kullander, Menezes, Oliveira & López-Fernández, 2023, and Hemeraia Varella, Kullander, Menezes, Oliveira & López-Fernández, 2023 (Varella et al. 2023). After this taxonomic review, Crenicichla labrina and Crenicichla brasiliensis were allocated to the genus Saxatilia, currently comprising 23 valid species (Varella et al. 2023; Fricke et al. 2025b). Zoosyst. Evol. 101 (4) 2025, 2161–2169 zse.pensoft.net 2167 Considering this, Sciadicleithrum araguariensis is presently known from two congeneric hosts belonging to Saxatilia. In addition, the new species described herein is also a parasite from a member of this genus. Furthermore, Crenicichla niederleinii Holmberg, 1891, the host of Sciadicleithrum joanae Yamada, Takemoto, Bellay & Pavanelli, 2009, became a nomen dubium, and its current taxonomic status is uncertain (Varella et al. 2023; Fricke et al. 2025b). The finding of two species of Sciadicleithrum on Saxatilia brasiliensis enhances our understanding of parasite biodiversity in the Neotropical Region, specifically within the Munim River Basin located in Maranhão State, and reinforces the host specificity of Sciadicleithrum species to cichlid hosts. The results presented provide data to answer questions of the systematics and taxonomy of Monopisthocotyla in a megadiverse region like the Neotropics. Acknowledgments The authors would like to thank the “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior” - CAPES (Funding Code 001) for the physical support provided for this study and for the scholarship to M.S.L. (88887.630333/2021-00); the team of the Laboratório de Sistemática e Ecologia de Organismos Aquáticos, especially Rafael O. Ferreira, Marcony S. P. Coelho, Diego S. Campos, Lucas de O. Vieira, and Antônio Francisco Bezerra for the support in the collection and transport of the hosts to the laboratory; and the collaborators Carine A. Bezerra and Yuri C. de Meneses for assistance in the parasite collection procedures. We thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the grant no. 307974/2021-9 to FPO. Figure 3. Sciadicleithrum araguariensis. A. Total, ventral; B. Copulatory complex; C. Vagina; D. Ventral anchor; E. Dorsal anchor; F. Ventral bar; G. Dorsal bar; H. Hook. Scale bars: 100 µm (A); 20 µm (B, D–G); 40 µm (C); 5 µm (I). zse.pensoft.net Silva, M.L. et al.: A new species of Sciadicleithrum 2168 References Albert JS, Destouni G, Duke-Sylvester SM, Magurran AE, Oberdorff T, Reis RE, Winemiller KO, Ripple WJ (2020) Scientists’ warning to humanity on the freshwater biodiversity crisis. Ambio 50: 85–94. https://doi.org/10.1007/s13280-020-01318-8 Avise JC, Hubbell SP, Ayala FJ (2008) À luz da evolução II: Biodiversidade e Extinção. The National Academies Press (EUA), Washington (DC), 414 pp. Azevedo-Santos VM, Rodrigues-Filho JL, Fearnside PM, Lovejoy TE, Brito MFG (2021) Conservation of Brazilian freshwater biodiversity: Thinking about the next 10 years and beyond. Biodiversity and Conservation 30(1): 235–241. https://doi.org/10.1007/s10531-020-02076-5 Azevedo-Santos VM, Daga VS, Tonella LH, Ruaro R, Arcifa MS, Fearnside PM, Giarrizzo T (2023) Brazil’s urban ecosystems threatened by law. Land Use Polyce 131: 106721. https://doi.org/10.1016/j. landusepol.2023.106721 Bellay S, Takemoto RM, Yamada FH, Pavanelli GC (2008) A new species of Sciadicleithrum (Monogenea, Ancyrocephalinae), gill parasite of Geophagus brasiliensis (Quoy & Gaimard) (Teleostei: Cichlidae) from reservoirs in the State of Parana. Zootaxa 1700(1): 63–68. https://doi.org/10.11646/zootaxa.1700.1.5 Bellay S, Takemoto RM, Yamada FH, Pavanelli GC (2009) Two new species of Sciadicleithrum (Monogenea: Dactylogyridae), gill parasites of Geophagus proximus (Castelnau) (Teleostei: Cichlidae), from the upper Parana River floodplain, Brazil. Zootaxa 2081(1): 57–66. https://doi.org/10.11646/zootaxa.2081.1.4 Brook BW, Bradshaw CJ, Koh LP, Sodhi, NS (2006) Momentum drives the crash: mass extinction in the tropics. Biotropica 38(3): 302–305. https://doi.org/10.1111/j.1744-7429.2006.00141.x Brooks TM, Mittermeier RA, Mittermeier CG, Da Fonseca GA, Rylands AB, Konstant WR, Flick P, Pilgrim J, Oldfield S, Magin G, Hilton‐Taylor C (2002) Habitat loss and extinction in the hotspots of biodiversity. Conservation biology 16(4): 909–923. https://doi. org/10.1046/j.1523-1739.2002.00530.x Carvalho AR, Tavares LER, Luque JL (2008) A new species of Sciadicleithrum (Monogenea, Dactylogyridae) parasitic on Geophagus brasiliensis (Perciformes, Cichlidae) from Guandu River, Southeastern Brazil. Acta Parasitologica 53: 237–239. https://doi. org/10.2478/s11686-008-0035-6 Ceballos G, Ehrlich PR, Barnosky AD, García A, Pringle RM, Palmer TM (2015) Accelerated modern human–induced species losses: Entering the sixth mass extinction. Science Advances 1(5): e1400253. https://doi.org/10.1126/sciadv.1400253 Darwall W, Bremerich V, Wever A, Dell AI, Freyhof J, Gessner MO, Grossart HP, Harrison I, Irvine K, Jähnig SC, Jeschke JM, Lee JJ, Lu C, Lewandowska AM, Monaghan MT, Nejstgaard JC, Patricio H, Schmidt-Kloiber A, Stuart SN, Thieme M, Tockner K, Turak E, Weyl O (2018) The alliance for freshwater life: A global call to unite efforts for freshwater biodiversity science and conservation. Aquatic Conservation Marine and. Freshwater Ecosystems 28: 1015–1022. https://doi.org/10.1002/aqc.2958 Fricke R, Eschmeyer WN, Fong JD (2025a) Species by family/subfamily. http://researcharchive.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp [Electronic version accessed 14 april 2025] Fricke R, Eschmeyer WN, van der Laan R (2025b) Eschmeyers Catalog of Fishes: Genera, species, references. http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp [Electronic version accessed 14 april 2025] Froese R, Pauly D (2024) FishBase. https://www.fishbase.se/Summary/ SpeciesSummary.php?id=47115&lang=portuguese_po Harrison I, Abell R, Darwall W, Thieme ML, Tickner D, Timboe I (2018) The freshwater biodiversity crisis. Science 362 (6421): 1368–1369. https://doi.org/10.1126/science.aav9242 Hogue AS, Breon K (2022) The greatest threats to species. Conservation Science and Practice 4(5): e12670. https://doi.org/10.1111/ csp2.12670 Humason GL (1979) Animal Tissue Techniques. 4th Edn, W.H. Freeman, San Francisco. Justo MCN, Nascimento LGA, Meneses YC, Trombeta T, Cohen SC (2020) Monogenoidea parasites of Oreochromis niloticus submitted to ractopamine supplemented diet from cultivated system. Arquivo Brasileiro de Medicina Veterinária e Zootecnia 72: 1980-1988. https://doi.org/10.1590/1678-4162-11652 Kritsky DC, Thatcher VE, Boeger WA (1986) Neotropical Monogenea. 8. Revision of Urocleidoides (Dactylogyridae, Ancyrocephalinae). Proceedings of the Helminthological Society of Washington 53(1): 1–37 Kritsky DC, Thatcher VE, Boeger WA (1989) Neotropical Monogenea. 15. Dactylogyrids from the gills of brazilian Cichlidae with proposal of Sciadicleithrum gen. n. (Dactylogyridae). Journal of the Helminthological Society of Washington 56(2): 128–140. Kritsky DC, Vidal-Martínez VM, Rodriguez-Canul R (1994) Neotropical Monogenoidea. 19. Dactylogyridae of cichlids (Perciformes) from the Yucatan Peninsula, with descriptions of three new species of Sciadicleithrum Kritsky, Thatcher and Boeger, 1989. Journal of the Helminthological Society of Washington 61(1): 26–33. López-Fernández H, Winemiller KO, Honeycutt RL (2010) Multilocus phylogeny and rapid radiations in Neotropical cichlid fishes (Perciformes: Cichlidae: Cichlinae). Molecular Phylogenetics and Evolution 55(3): 10701086. https://doi.org/10.1016/j.ympev.2010.02.020 Melo MFC, Santos JN, Santos CP (2012) Sciadicleithrum juruparii n. sp. (Monogenea: Ancyrocephalidae) from the gills of Satanoperca jurupari (Heckel) (Osteichthyes: Cichlidae) in the Guama River, Amazon Delta, Brazil. Systematic Parasitology 82: 125–129. https:// doi.org/10.1007/s11230-012-9353-z Mendoza-Franco EF, Aguirre-Macedo ML (2007) New and previously described species of Dactylogyridae (Monogenoidea) from the gills of Panamanian freshwater fishes (Teleostei). The Journal of Parasitology 93(4): 761–771. https://doi.org/10.1645/GE-1068R.1 Mendoza-Franco EF, Scholz T, Vidal-Martínez VM (1997) Sciadicleithrum meeki sp. nov. (Monogenea: Ancyrocephalinae) from the gills of Cichlasoma meeki (Pisces: Cichlidae) from cenotes (= Sinkholes of the Yuctan Penísula, México). Folia Parasitologica 44: 205–208. Mendoza-Franco EF, Scholz T, Rozkošna P (2010) Tucunarella n. gen. and other dactylogyrids (Monogenoidea) from cichlid fish (perciformes) from peruvian Amazonia. The Journal of Parasitology 96(3): 491–498. https://doi.org/10.1645/GE-2213.1 Mendoza-Palmero CA, Blasco-Costa I, Hernández-Mena D, PérezPonce de León G (2017) Parasciadicleithrum octofasciatum n. gen., n. sp. (Monogenoidea: Dactylogyridae), parasite of Rocio octofasciata (Regan) (Cichlidae: Perciformes) from Mexico characterised by morphological and molecular evidence. Parasitology International 66(2): 152–162. https://doi.org/10.1016/j.parint.2017.01.006 . Zoosyst. Evol. 101 (4) 2025, 2161–2169 zse.pensoft.net 2169 Mizelle JD, Price CE (1963) Additional Haptoral Hooks in the Genus Dactylogyrus. The Journal of Parasitology 49(6): 1028–1029. doi:https://doi.org/10.2307/3275746 Morey GAM, Arimuya MV, Boeger WA (2019) Neotropical Monogenoidea 62. Biotodomella mirospinata gen. nov., sp. nov. (Polyonchoinea: Dactylogyridae): a parasite of the gills of Biotodoma cupido (Cichliformes: Cichlidae), from the Peruvian Amazon. Zoologia 36: e38455. https://doi.org/10.3897/zoologia.36.e38455 Morey GAM, Dávila HA, Arimuya MV, Sousa AL, Cruces CL, Chero JD (2024) Three New Species of Sciadicleithrum (Monogenoidea, Dactylogyridae) Parasitizing Cichlid Fishes (Cichliformes: Cichlidae) in the Northeastern Peru. Acta Parasitologica 69: 1674–1681, 2024. https://doi.org/10.1007/s11686-024-00895-y Ottoni FP, South J, Azevedo-Santos VM, Henschel E and de Bragança PHN (2023) Editorial: Freshwater biodiversity crisis: Multidisciplinary approaches as tools for conservation. Frontiers in Environmental Science 11: 1155608. https://doi.org/10.3389/fenvs.2023.1155608 Pariselle A, Boeger WA, Snoeks J, Bilong Bilong CF, Morand S,Vanhove MPM (2011) The monogenean parasite fauna of cichlids: A potential tool for host biogeography. International Journal of Evolutionary Biology 2011: 1–15. https://doi.org/10.4061/2011/471480 Paschoal F, Schols T, Tavares-Dias M, Luque JL (2016) Dactylogyrids (Monogenea) parasitic on cichlids from northern Brazil, with description of two new species of Sciadicleithrum and new host and geographical records. Acta Parasitologica 61: 158–164. https://doi. org/10.1515/ap-2016-0021 Pereira Júnior A, Pereira E (2017) Degradação ambiental e a diversidade biológica/biodiversidade: uma revisão integrativa. Enciclopédia Biosfera 14(26): 922937. https://doi.org/10.18677/EnciBio_2017B79 Pimm SL, Jenkins CN, Abell R, Brooks TM, Gittleman JL, Joppa LN, Raven PH, Roberts CM, Sexton JO (2014) The biodiversity of species and their rates of extinction, distribution, and protection. Science, 344(6187): 1246752-1-10. https://doi.org/10.1126/science.1246752 Reid AJ, Carlson AK, Creed IF, Eliason EJ, Gell PA, Johnson PTJ, Kidd KA, MacCormack TJ, Olden JD, Ormerod SJ, Smol JP, Taylor WW, Tockner K, Vermaire JC, Dudgeon D, Cooke SJ (2019) Emerging threats and persistent conservation challenges for freshwater biodiversity. Biological Reviews 94 (3): 849–873. https://doi. org/10.1111/brv.12480 Savage JM (1995) Systematics and the biodiversity crisis. BioScience 45(10): 673–679. https://doi.org/10.2307/1312672 Seidlová L, Benovics M, Šimková A (2022) Gill monogeneans of neotropical cichlid fish: diversity, phylogenetic relationships, and host-parasite cophylogenetic associations International Journal for Parasitology 52(9): 603–615. https://doi.org/10.1016/j.ijpara.2022.05.001 Singh JS (2002) The biodiversity crisis: a multifaceted review. Current Science 82(6): 638–647. https://www.jstor.org/stable/24106689 Smith WS, Chakrabarty P, Sparks JS (2008) Phylogeny, taxonomy, and evolution of Neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics 24(5): 625–641. https://doi.org/10.1111/j.10960031.2008.00210.x Tavares-Dias M, Silva LMA, Oliveira MSB (2022) Geographic range, distribution patterns and interactions of Monogenea Van Beneden 1858, with species of native host freshwater fishes from Brazil. Revista Brasileira de Parasitologia Veterinária 31(3): e005722 https:// doi.org/10.1590/s1984-29612022048 Tickner D, Opperman JJ, Abell R, Acreman M, Arthington AH, Bunn SE, Cooke SJ, Dalton J, Darwall W, Edwards G, Harrison I, Hughes K, Jones T, Leclère D, Lynch AJ, Leonard P, McClain ME, Muruven D, Olden JD, Ormerod SJ, Robinson J, Tharme RE,Thieme M,Tockner K, Wright M, Young L (2020) Bending the curve of global freshwater biodiversity loss: An Emergency Recovery Plan. BioScience 70(4): 330–342. https://doi.org/10.1093/biosci/biaa002 Varella HR, Kullander SO, Menezes NA, Oliveira C, López-Fernández H (2023) Revision of the generic classification of pike cichlids using an integrative phylogenetic approach (Cichlidae: tribe Geophagini: subtribe Crenicichlina). Zoological Journal of the Linnean Society 198(4): 982–1034. https://doi.org/10.1093/zoolinnean/zlad021 Vidal-Martínez VM, Scholz T, Aguirre-Macedo ML (2001) Dactylogyridae os cichlid fishes from nicaragua, Central America, with descriptions of Gussevia herotilapiae sp. nov. and three new species of Sciadicleithrum (Monogenea: Ancyrocephalinae). Comparative Parasitology 68(1):76–86. Vieira LO, Campos DS, Oliveira RF, South J, Coelho MSP, Paiva MJS, Bragança PHN, Guimarães EC, Katz AM, Brito PS, Santos JP, Ottoni FP (2023) Checklist of the fish fauna of the Munim River Basin, Maranhão, northeastern Brazil. Biodiversity Data Journal 11(2): e98632. https://doi.org/10.3897/BDJ.11.e98632 Wayne SR (2010) National Institutes of Health: ImageJ. https://imagej. nih.gov/ij/download.html Yamada FH, Takemoto RM, Bellay S, Pavanelli GC (2009) Two new species of Sciadicleithrum (Monogenea, Dactylogyridae) parasites of Neotropical cichlid fishes from the Parana River, Brazil. Acta Parasitologica 54(1): 6–11. https://doi.org/10.2478/s11686-009-0004-8