Rhabdochona fuscovaria Alcantara & Úngari & Ferreira-Silva & Emmerich & Pinheiro & O´Dwyer & Silva 2021, n. sp.

Rhabdochona fuscovaria n. sp. Alcantara, O´Dwyer & Silva (Figure 2–4) Description (based on one male and one female). Body narrow, elongate. Medium-sized nematodes with lightly transversely striated cuticle. Sexual dimorphism evident. Lateral alae present. Oval oral aperture surrounded by four lateral plates, four cephalic papillae and two amphids. Prostom funnel-shaped, relatively short with basal teeth, anterior margin of prostom armed internally with 14 teeth (7 dorsal and 7 ventral). Vestibule relatively long, straight. Deirids small, simple, stylet-shaped, anterior to mid-length of vestibule. Glandular oesophagus longer than muscular oesophagus. Tail tip of both sexes conical. Males without caudal alae; spicules unequal and dissimilar. Male. Body 11.10 mm long and 98.8 wide. Vestibule including prostom 141.1 long and 7.4 wide; prostom 25 long and 10.1 wide in lateral view. Muscular oesophagus 362.8 long, 26.2 wide; glandular oesophagus 1.82 mm long, 71.4 wide; length ratio of both parts of oesophagus 1:5. Entire oesophagus and vestibule representing 20.9% of body length. Nerve ring encircling muscular oesophagus, 206.4 from anterior end of body. Excretory pore and deirids 321.9 and 56.3 from anterior extremity, respectively. Nine pairs precloacal papillae, 8 subventral pairs and 1 lateral pair (between the 3 rd and 4 th subventral pairs). Nine postcloacal papillae pairs: 7 ventral pairs and 2 ventrolateral pairs (one between the 1 st and 2 nd pairs and 1 after the last ventral papillae pair). Longitudinal ventral cuticular ridges (area rugosa) absent. Longer (left) spicule 585.7 long; shaft 285.3 long, representing 48.7% of entire spicule length; distal tip slightly widened, moderately dilated; right spicule boat-shaped, 132.9 long, without dorsal barb at distal tip. Length ratio of spicules 1:4.4. Tail 452.5 long. Female. Body 16.65 mm long and 139.4 wide. Vestibule including prostom 143.3 long and 8.6 wide, prostom 31 long and 15.9 wide. Muscular oesophagus 358.5 long, 32.1 wide; glandular oesophagus 2.14 mm long, 69.2 wide; length ratio of both parts of oesophagus 1:5.9. Entire oesophagus and vestibule representing 15.8% of body length. Nerve ring, excretory pore and deirids 222.5, 333.1, and 77.4 from anterior extremity, respectively. Tail conical, 334.4 long. Vulva postequatorial, 9.26 mm from anterior extremity, at 55.6% of body length; vulval lips not elevated. Muscular vagina directed posteriorly from vulva. Eggs oval, numerous, with no filaments, thick-walled, embryonated, size 29.2–35.4 × 15.7–22.8, with smooth surface. Taxonomic summary Type locality: São Sebastião do Paraíso farm (21°50’41.83”S, 48°28’10.24”W), municipality of Boa Esperança do Sul, São Paulo State, Brazil. Type host: Scinax fuscovarius (A. Lutz, 1925). Site of infection: Stomach. Prevalence: one host infect of four frogs examined. Type material: Holotype (CHIOC 39104), adult male; and Allotype (CHIOC 39105), adult female (deposited in the Helminthological Collection of the Instituto Oswaldo Cruz - CHIOC, after acceptance of the manuscript) Zoobank number: http://zoobank.org/ urn:lsid:zoobank.org:act: 01B5EC2C-7AAD-44A2-B0F8-C87AA77AE83A. ......continued on the next page ......continued on the next page ......continued on the next page ......continued on the next page ......continued on the next page Etymology: The epithet refers to the name of the host, which is the first anuran described as a host of Rhabdocona in the Americas. Remarks. Moravec (2010) argued that the South American Rhabdochona spp. probably derived from the North American species since they have no similarity with African congeners. Despite this, we have compared the new species with all others from the Nearctic and Neotropical regions. Rhabdochona fuscovaria sp. n. differs from all congeneric species by the combination of a unique set of morphological characters including the following: 1) morphology of deirids, 2) presence of 14 anterior prostomal teeth, 3) caudal alae absent; 4) morphology of spicules, 5) eggs with no filaments, and 6) caudal papillae arrangement (9:0:9). The nematode genus Rhabdochona Railliet, 1916 comprises about 100 species (Moravec 2010). Rhabdochona fuscovaria sp. n. has 14 teeth in the prostom. In the Americas, 14 Rhabdochona spp. have the same characteristic (Table 1). Of these, 10 species occour in the Neartic region (R. canadensis Moravec & Arai, 1971, Rhabdochona canadensis bifilamentosa Moravec & Huffman, 1988, R. cascadilla Wigdor, 1918, R. catostomi Kayton, Kritsky & Tobias, 1979, R. cotti Gustafson, 1949, R. decaturensis Gustafson, 1949, R. ictalurid Aguilar-Aguilar, Rosas-Valdez & Pérez-Ponce de León, 2010, Rhabdochona kidderi texensis Moravec & Huffman, 1988, R. milleri Choquette, 1951, and Rhabdochona zacconis Yamaguti, 1935) and four in the Neotropical region (R. acuminata Molin, 1860, R. kidderi kidderi Pearse, 1936, Rhabdochona osorioi Santacruz, García & Pérez-Ponce de León, 2019, and Rhabdochona uruyeni (Diaz-Ungrfa, 1968). However, among the 14 species that present 14 teeth, only five species have simple deirids like Rhabdochona fuscovaria sp. n., as follow: R. acuminata, R. cotti, R. decaturensis, R. osorioi, and R. uruyeni. Rhabdochona acuminata is found in a wide array of distantly related hosts (Characiformes and Siluriformes) (Cremonte et al. 2002; Ramallo 2005; Pinto et al. 2010). This species is similar to the new species in both possessing 14 teeth in the prostom, single deirids, and postequatorial vulva. However, Rhabdochona fuscovaria sp. n. can be readily distinguished from R. acuminata by the number of postanal papillae in males (9 pairs vs 6–7 pairs). Rhabdochona cotti is a parasite of the instestine of Scorpaeniformes from USA and Canada (Moravec & Muzzall 2007). This species can be easily differentiated from the new species by the presence of eggs with filaments. In addition, Rhabdochona fuscovaria sp. n. differs from R. cotti by the number post caudal papillae (9 pairs vs. 6 pairs, respectively). Rhabdochona decaturensis, a parasite of Perciformes in the USA and Canada (Gustafson 1949, Moravec &Arai 1971) has a spicule exceeding a length of 1 mm, while the spicule Rhabdochona fuscovaria sp. n. is small (585.7 µm long). Additionally, the new species differs from R. decaturensis species by the caudal papillae arrangement (9:0:9 vs. 7-9:0:6). Rhabdochona osorioi is a parasite of Characiformes freshwater fishes from Mexico (Santa Cruz et al. 2019). This species differs from Rhabdochona fuscovaria sp. n. in the left spicule, which is smaller than the new species (414–451 vs 585.7). The new species has 18 caudal papillae pairs while R. osorioi has 22 pairs. Rhabdochona uruyeni, a parasite found in South American Characiformes and Sciaenidae freshwater fishes (Pinto et al. 2010), differs in the number of caudal papillae, the tail size, and oesophagus size: Rhabdochona fuscovaria sp. n. has 9 preclocal papilla pairs and 9 postcloacal papilla pairs, tail 452.6 long, muscular esophagus 362.8 long: Rhabdochona uruyeni has 8-10 pairs precloacal papillae and 5 pairs + 1 postcloacal papillae, tail 180–230 long, and a muscular esophagus 120–150 long.

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