Rhabdochona fuscovaria sp. n. (Nematoda: Rhabdochonidae) from the stomach of frog Scinax fuscovarius (Anura: Hylidae) in Brazil Author Alcantara, Edna Paulino De 0000-0002-2982-9336 Division of Parasitology, DBBVPZ, São Paulo State University, Campus Botucatu Brazil, Research and Teaching Laboratory of Wild Animals, São Paulo, Brazil & https: // orcid. org / 0000 - 0002 - 2982 - 9336 Author Úngari, Leticia Pereira 0000-0002-3087-2614 Division of Parasitology, DBBVPZ, São Paulo State University, Campus Botucatu Brazil, Research and Teaching Laboratory of Wild Animals, São Paulo, Brazil & https: // orcid. org / 0000 - 0002 - 3087 - 2614 Author Ferreira-Silva, Cristiana 0000-0002-1946-4409 Division of Parasitology, DBBVPZ, São Paulo State University, Campus Botucatu Brazil, Research and Teaching Laboratory of Wild Animals, São Paulo, Brazil & https: // orcid. org / 0000 - 0002 - 1946 - 4409 Author Emmerich, Enzo 0000-0002-9367-368X Division of Parasitology, DBBVPZ, São Paulo State University, Campus Botucatu Brazil, Research and Teaching Laboratory of Wild Animals, São Paulo, Brazil & https: // orcid. org / 0000 - 0002 - 9367 - 368 X Author Pinheiro, Raul Henrique Da Silva 0000-0003-3221-5017 Laboratório de Histologia e Embriologia Animal, Instituto da Saúde e Produção Animal, Universidade Federal Rural da Amazônia, Belém, Pará, Brasil. https: // orcid. org / 0000 - 0003 - 3221 - 5017 Author O´Dwyer, Lucia Helena 0000-0002-3426-6873 Division of Parasitology, DBBVPZ, São Paulo State University, Campus Botucatu Brazil, Research and Teaching Laboratory of Wild Animals, São Paulo, Brazil & https: // orcid. org / 0000 - 0002 - 3426 - 6873 Author Silva, Rein- Aldo José Da Division of Parasitology, DBBVPZ, São Paulo State University, Campus Botucatu Brazil, Research and Teaching Laboratory of Wild Animals, São Paulo, Brazil text Zootaxa 2021 2021-11-12 5067 4 569 584 journal article 3553 10.11646/zootaxa.5067.4.5 b2f6a497-7a04-46af-b0a6-cacc97561526 1175-5326 5683457 0A9BFD04-929A-485F-A7C8-DFE22E0D2AD9 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 . FIGURE 2. Rhabdochona fuscovaria sp. n. male specimen. A) anterior end; B) Posterior end showing the spicules and papillae; C) Left spicule; D) Detail of the left spicule end; E) Right spicule. Scale bar: A, C - 100 µm; B - 200 µm; D - 25 µm; E - 50 µm. FIGURE 3. Rhabdochona fuscovaria sp. n. female specimen.A) anterior end; B) Mouth; C) Vulva region showing the muscular vagina and eggs; D) Tail; E) Egg. Scale bar: A, D - 100 µm; B - 5 µm; C - 50 µm; E - 25 µm. FIGURE 4. A) Anterior end of Rhabdochona fuscovaria sp. n. female specimen; B) Mouth of Rhabdochona fuscovaria sp. n. of the female specimen.* = amphids; CP = cephalic papillae; Arrow: lateral plates; C) Vulvar region of Rhabdochona fuscovaria sp. n. TABLE 1. Morphological data of Rhabdochona spp. from the Neartic and Neotropical regions (all measurements in µm, except when indicated). Abbreviations: S, sex; M, male; F, female; L, body length; W, body width; P, prostom; T, teeth number in the prostom; VPL, vestibule including prostom length; MEL, muscular oesophagus length; GEL, glandular oesophagus length; NR, nerve ring; EP, excretory pore; D, deirids; DS, deirids shape; LSL, left spicule length; RSL, right spicule length; SSL, spicule shaft length; CP, caudal papillae arrangement (represented as precloacal; postcloacal); and TL, tail length.

Species	S	L (mm)	W	P	T	VPL	MEL	GEL (mm)	NR
Neartic region (14 spp.)
Rhabdochona canadensis	M	5.74–8.36	209–150	15–21	14	120–165	186–306	2.18–3.90	177–207
F	9.88–27.92	190–408	21–33	144–195	300–510	3.26–5.07	219–270
Rhabdochona canadensis bifilamentosa	M	4.19–5.37	109–136	18–21	14	96–108	177–201	1.48–1.69	132–174
F	5.75–9.78	156–258	24–36	14	117–135	219–258	1.54–2.38	162–192
Rhabdochona cascadilla	M	4.0–5.1	12–19	14	92	146–227	0.8–1.8	118–134
F	6.4–9.9	19–27	113	175–227	1.1–1.6	134–159
Rhabdochona catostomi	M	8.9–14.3	173–211	22–34	14	134–174	336–372	3.5–4.8	204–238
F	15.3–16.7	248–292	28–31	154–176	375–417	4.97–6.10	227–284
Rhabdochona cotti	M	4.56–6.57	95–122	15	14	84–96	177–243	0.55–0.79	144–192
F	13.99–16.80	177–272	21	105–129	231–330	0.86–1.51	195–286
Rhabdochona decaturensis	M	6.8–13.29	85–132	15–18	14	96–120	210–270	1.70–3.52	40–180
F	9.2–21.3	93–198	16–25	90–120	217–320	1.92–4.38	150–183
Rhabdochona ictaluri	M	6.4–6.9	105–120	18–21	14	94–101	185–210	1.79–2.14	142–159
F	9.78–13.56	137–175	24–25	93–103	260–278	2.43–2.64	161–186
Rhabdochona kidderi texensis	M	5.01–8.19	82–95	15–18	14	126–144	258–360	1.59–2.05	171–195
F	9.0–15.83	122–218	18–24	135–159	330–405	1.93–2.49	186–225
Rhabdochona kisutchi	M	6.61–8.41	110–150	24–27	10	108–153	225–270	1.35–2.29	168–240
F	12.04–17.38	190–272	30–36	126–198	285–361	2.34–3.36	174–276
Rhabdochona longleyi	M	7.3–9.7	82–136	15–18	6	93–120	150–195	0.46–0.67	135–180
F	8.62–15.97	109–163	15–18	14	99–132	147–195	0.51–0.72	135–165
Rhabdochona milleri	M	6.94	176	18	14	144	300	1.36	168
F	10.91–12.10	136–163	21–24	111–138	270–297	1.59–2.35	186–189

......continued on the next page TABLE 1. (Continued)

Species	S	L (mm)	W	P	T	VPL	MEL	GEL (mm)	NR
Neartic region (14 spp.)
Rhabdochona ovifilamenta	M	6.55–8.02	95–136	16	111–138	255–300	1.90–3.59	156–204
F	11.75–21.76	204–258	30–39	90–135	276–558	1.60–4.42	126–210
Rhabdochona xiphophorasi	M	6.12	132	19	6	108	171	1.41	168
F	6.14–10.05	178–227	19–29	102–112	201–237	1.39–2.07	165–171
Rhabdochona zacconis	M	6.69–10.06	122–177	18–21	14	135–207	279–390	2.45–4.90	192–237
F	16.32–18.31	245–285	30–33	177–210	450–525	4.15–5.98	264–309
Neotropical region (13 spp.)
R. fuscovaria n. sp.	M	11.1	98.8	25	14	141.1	362.8	1.8	206.4
F	16.7	139.4	31	143.3	358.5	2.1	222.5
R. acuminata	M	6.30–10.22	81–122	15–27	14	123–150	270–360	1.18–1.96	156–207
F	10.69–20.54	95–272	21–36	144–156	321–476	1.44–4.41	204–270
R. ahuehuellensis	M	3.16–6.36	60–110	12–18	10	69–120	102–210	0.95–1.74	99–180
F	2.75–8.92	50–120	11–20	20–188	74–307	0.86–1.57	67–213
R. cubensis	M	3.16	68	12	6	90	141	1.01	120
F	4.56–8.43	95–122	10–15	81–105	147–186	1.18–190	117–159
R. fabianae	M	4.10–6.37	90–130	20–30	16	110–130	150–200	1.11–2.02	140–170
F	9.67–13.97	200–330	37–45	140–230	270–420	2.21–3.38	170–240
R. guerreroensis	M	3.69–7.52	75–162	16–18	12	92–126	138–228	0.69–1.26	131–195
F	6.35–14.57	142–276	23–27	94–118	195–299	1.11–1.81	131–196
R. kidderi kidderi	M	5.13–6.46	54–95	12–18	14	111–135	246–306	1.21–1.58	162–183
F	9.89–13.65	122–163	18–24	129–156	333–411	1.63–2.19	129–156
R. lichtenfelsi	M	6.47–8.52	57–100	18–22	10	95–108	174–270	1.02–1.45	162–186
F	9.14–14.88	93–125	21–30	96–183	225–321	1.25–169	161–198

......continued on the next page TABLE 1. (Continued)

Species	S	L (mm)	W	P	T	VPL	MEL	GEL (mm)	NR
Neotropical region (13 spp.)
R. mexicana	M	4.55–9.23	79–188	19–26	10	115–161	184–280	1.50–4.55	135–188
F	8.90–18.18	155–300	23–33	102–234	214–425	2.40–5.41	165–250
R. osorioi	M	7.8–10.5	163–200	23–34	14	112–128	221–342	1.8–3.2	125–169
F	11.6–27.3	154–327	24–41	112–128	173–436	147–227
R. salgadoi	M	1.98–2.29	66–75	13–14	16	56–82	99–112	0.603–0.726	99–115
F	3.33–4.08	105–115	16–19	69–82	138–161	0.808–0.957	101–132
R. uruyeni	M	6.92–8.90	120–150	19–30	14	120–150	1.48–1.72	160–180
F	10.8–12	120–170	38–46	126–135	200–250	2.10–2.30	150–170
R. xiphophori	M	6.12	132	19	6	108	171	1.41	168
F	6.14–10.05	178–227	19–29	102–112	201–237	1.39–2.07	165–171

......continued on the next page TABLE 1. (Continued)

Species	EP	D	DS	LSL	RSL	SSL	CP	TL	References
Neartic region (14 spp.)
Rhabdochona canadensis	237–279	51–69	B	471–525	02–129	9 + 7, 7 + 7, 8 +8 e 9 +9; 6 pairs	270–390	Moravec & Arai 1971
351–420	63–78	216–309
Rhabdochona canadensis bifilamentosa	180–282	45–66	B	396–480	93–114	213–240	7+7, 7+8, 8+9, 9+6, 10+10 and 1 lateral pair; 6 pairs	243–300	Moravec & Huffman 1988
222–282	57–78	147–174
Rhabdochona cascadilla	182–210	39–54	B	320–415	103–128	153–190	7 + 7 e 9 + 10; 6 paris	212–322	Wigdor 1918
200–266	50–62	184–287
Rhabdochona catostomi	484	76–85	B	546–562	151–154	8–9 pairs; 5 pairs	336–392	Kayton et al . 1979
90–97	227–280
Rhabdochona cotti	216–252	51–63	S	378–478	90–114	168–195	8 + 8, 8 + 9, 9 + 9 and 9 + 10 and 1 pair of preanal papillae; 6 pairs	207–249	Moravec & Muzzall 2007
330–336	60–75	258–300
Rhabdochona decaturensis	210–273	S	830–1,070	75–100	7–8 pares; 6 pairs	250–310	Gustafson 1949; Moravec & Arai, 1971
236–270	160–230
Rhabdochona ictaluri	79–86	B	445–544	72–92	190–206	8+7, 8+9, 9+9 and 1 pair of pre- anal papillae; 6 pairs	70–160	Aguilar-Aguilar et al . 2010
73–79	70–390
Rhabdochona kidderi texensis	216–288	63–69	B	1,670–2,080	84–102	525–684	4 + 5, 5 + 5, 5+ 6, 6 + 6, 6+7, 7 +7 and 1 pair of preanal papillae; 6 pairs	252–264	Moravec & Huffman 1988
285–321	72–87	147–225
Rhabdochona kisutchi	249–351	60–75	B	564–660	87–135	9 pares, 7+8, 8+8, 8+9, 7+9, 8+10, and 10+10; 6 pairs	300–390	Margolis et al . 1975
411–420	60–96	351–450
Rhabdochona longleyi	213–285	51–60	S	420–501	93–102	240–291	6+8, 8+8, 8+9, 9+9, 9+10 and 1 lateral pair; 6 pairs	261–390	Moravec & Huffman 1988
233–368	42–57	264–368

......continued on the next page TABLE 1. (Continued)

Species	EP	D	DS	LSL	RSL	SSL	CP	TL	References
Neartic region (14 spp.)
Rhabdochona milleri	237	63	B	402	129	9 pairs; 6 pairs	300	Moravec & Arai 1971
261	63–81	210–243
Rhabdochona ovifilamenta	237–264	51–78	B	390–420	105–117	6+7, 7+9, 8+9 and 9+10; 6 pairs	303–372	Moravec & Arai 1971
243	39–60	294–315
Rhabdochona xiphophorasi	204	49	B	297	85	174	9+10; 6 pairs	224	Caspeta-Mandujano et al ., 2001
254–287	39–46	145–260
Rhabdochona zacconis	300	75–90	B	435–510	108–120	7+8, 8+9 and 9+9; 6 pairs	354–411	Moravec et al . 1981
414–453	105–123	273–303
Neotropical region (13 spp.)
R. fuscovaria n. sp.	321.9	56.3	S	585.7	132.9	285.3	9 pairs; 9 pairs	452.6	Present study
333.1	77.4	334.4
R. acuminata	237	15–51	S	576–591	81–120	8+8, 10+11; 6–7 pairs	243–375	Cremonte et al . 2002
172–400	60	225–240
R. ahuehuellensis	126–257	16–52	B	127–248	41–73	61–116	8–11 pairs; 6 pairs	80–219	Mejía-Madrid et al . 2003
70–306	25–86	96–278
R. cubensis	171	63	B	366	69	246	7+6; 6 pairs	180	Moravec & Coy-Otero, 1987
195–233	66–90	78–165
R. fabianae	170–280	33–67	B	530–610	87–107	7 pairs; 6 pairs	90–180	Ramallo 2005
270–370	50–100	40–120
R. guerreroensis	170–213	24–41	B	255–335	92–140	138–193	13 pairs; 9 pairs	352–528	Caspeta-Mandujano et al . 2002
188–318	25–60	230–345
R. kidderi kidderi	222–288	60–75	B	735–840	87–90	372–426	5–7 pairs; 6 pairs	225–291	Moravec & Arai 1971
240–345	63–83	177–231

......continued on the next page TABLE 1. (Continued)

Species	EP	D	DS	LSL	RSL	SSL	CP	TL	References
Neotropical region (13 spp.)
R. lichtenfelsi	197–243	30–51	B	387–454	90–108	234–304	8 pairs; 6 pairs	252–324	Sánchez-Alvarez et al . 1998
204–279	36–57	228–285
R. mexicana	204–306	39–59	B	468–587	82–108	138–178	5+4, 5+3; 6 pairs	165–217	Caspeta-Mandujano et al . 2000
250–359	52–75	101–224
R. osorioi	202–249	39–49	S	414–451	117–138	251–273	15 pairs; 7 pairs (occasionally 7+6)	151–347	Santacruz et al . 2019
173–240	39–45	218–364
R. salgadoi	141–188	33–49	B	226–240	59–92	115–135	8–9 pairs; 6 pairs	108–161	Caspeta-Mandujano & Moravec 2000
151–237	56–59	101–224
R. uruyeni	120–150	S	320–456	70–120	8–10 pairs; 5 pairs + 1	180–225	Pinto et al . 2010
150–190	40–60	300
R. xiphophori	204	49	B	297	85	174	10 pairs; 6 pairs	224	Caspeta-Mandujano et al ., 2001
254–287	39–46	145–260

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.