Systematic assessment of the <i>Hypomasticus steindachneri</i> (Characiformes: Anostomidae) species complex, with the description of a new species

Ito, Ian Solon B.; Souza-Shibatta, Lenice; Oyakawa, Osvaldo T.; Garavello, Júlio C.; Britski, Heraldo A.; Birindelli, José L. O.

doi:10.1590/1982-0224-2025-0003

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Original Article • Neotrop. ichthyol. 23 (03) • 2025 • https://doi.org/10.1590/1982-0224-2025-0003 linkcopy

Systematic assessment of the Hypomasticus steindachneri (Characiformes: Anostomidae) species complex, with the description of a new species

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Abstract

This study provides a taxonomic revision of Hypomasticus steindachneri,based on an extensive analysis of specimens from various basins along the Brazilian coastal region. Specimens were analyzed using molecular and morphological methodologies for the purpose of species delimitation. Hypomasticus steindachneri is redescribed with an integration of new evidence and data from the holotype, and a new species is described from the Southeast Atlantic Forest. The new species is diagnosed from its congeners by the following combination of features: 12 scale rows around the caudal peduncle, a subterminal mouth with cleft aligned longitudinally with the ventral margin of the second infraorbital bone and three diffuse dark midlateral blotches, extending horizontally by 4–5 scales and vertically by 2–3 rows of scales. Osteological examination revealed notable findings, including the first record of pronounced hypertrophy in the first pair of ribs within the genus, which may be related to mating behaviors. Additionally, a bar formed by the processes of the orbitosphenoid and parasphenoid bones was identified. The clear delimitation of new, undescribed species in the phylogenetic analysis highlights the need for a comprehensive taxonomic review of the genus Hypomasticus, utilizing new sets of molecular and morphological evidence.

Keywords:
Atlantic Forest; Coastal drainages; Integrative taxonomy; Osteology; Species delimitation

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Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Departamento de Biologia Animal e Vegetal, CCB, Universidade Estadual de Londrina, Rodovia Celso Garcia Cid, Km 380, Cidade Universitária, 86055-900, Londrina, Paraná, Brazil, Phone +55(43)3371-5151 - Londrina - PR - Brazil
E-mail: neoichth@nupelia.uem.br

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Taxon	Voucher	Locality	Basin	Acession	References
H. cf. steindachneri	LBP 7502-35577	Rio Juquiá	Ribeira de Iguape	PX391179	Present study
H. cf. steindachneri	LBP 7502-35578	Rio Juquiá	Ribeira de Iguape	PX391180	Present study
H. cf. steindachneri	LBP 7444-35781	Lagoa Jurumirim	Ribeira de Iguape	FBCR032-09	Bold System
H. cf. steindachneri	LBP 26376-91938	Rio Poço Verde	Una do Prelado	PX391181	Present study
H. cf. steindachneri	LBP 2380-16073	Lagoa Feia	Rio de Janeiro	HM065002	Pereira et al. (2011)
H. cf. steindachneri	LBP 18618-49708	Rio Macabú	Rio de Janeiro	MT427927.1	Birindelli et al. (2020)
H. cf. steindachneri	LBP 10727-49707	Rio Macabú	Rio de Janeiro	MT427926.1	Birindelli et al. (2020)
H. cf. steindachneri	MCNIP 1465	Rio Mucuri	Mucuri	MUCU038-13	Bold System
H. cf. steindachneri	MCNIP 1396-1	Rio Mucuri	Mucuri	MUCU171-14	Bold System
H. cf. steindachneri	MCNIP 1396-2	Rio Mucuri	Mucuri	MUCU161-14	Bold System
H. cf. steindachneri	MCNIP 1396-3	Rio Mucuri	Mucuri	MUCU162-14	Bold System
H. cf. steindachneri	MCNIP 1466	Rio Mucuri	Mucuri	MUCU190-13	Bold System
H. cf. steindachneri	MZUEL 16474	Rio Pardo	Pardo	PX391179	Present study
H. cf. steindachneri	MZUEL 17996	Rio Pardo	Pardo	PX391180	Present study
H. steindachneri	JEQUI 4034	Rio Itacambiruçu	Jequitinhonha	JEQUI045-12	Pugedo et al. (2016)
H. steindachneri	JEQUIJQ 48	Rio Jequitinhonha	Jequitinhonha	JEQUI091-12	Pugedo et al. (2016)
H. steindachneri	JEQUIJQ 47	Rio Jequitinhonha	Jequitinhonha	JEQUI090-12	Pugedo et al. (2016)
H. steindachneri	JEQUI 6009	Rio Jequitinhonha	Jequitinhonha	JEQUI132-12	Pugedo et al. (2016)
H. steindachneri	JEQUI 6023	Rio Itacambiruçu	Jequitinhonha	JEQUI134-12	Pugedo et al. (2016)
H. steindachneri	JEQUILGC 2984	Rio Araçuai	Jequitinhonha	JEQUI224-13	Pugedo et al. (2016)
H. steindachneri	JEQUILGC 2983	Rio Araçuai	Jequitinhonha	JEQUI223-13	Pugedo et al. (2016)
H. steindachneri	MCNIP 379	Rio Jequitinhonha	Jequitinhonha	KF568994.1	Ramirez et al. (2016)
H. thayeri	LGC 5784	Rio Santo Antônio do Cruzeiro	Doce	MK770210	Mendes et al. (unpub.)
H. copelandii	LGC 7107	Rio Paraíba do Sul	Paraíba do Sul	MK770216	Mendes et al. (2022)
H. copelandii	LGC 7108	Rio Paraíba do Sul	Paraíba do Sul	MK770217	Mendes et al. (2022)
H. copelandii	LGC 7109	Rio Paraíba do Sul	Paraíba do Sul	MK770218	Mendes et al. (2022)
H. copelandii	LGC 5393	Rio Corrente Grande	Doce	MK770205	Mendes et al. (2022)
H. copelandii	LGC 5394	Rio Corrente Grande	Doce	MK770206	Mendes et al. (2022)
H. copelandii	MCNIP 459	Rio Manhuaçu	Doce	KF568978.1	Ramirez et al. (2016)
H. mormyrops	MZUEL 8022	Rio Bananal	Paraíba do Sul	KX020572	Ramirez et al. (2016)
H. mormyrops	LBP 8103-37539	Rio Pomba	Paraíba do Sul	MT427916	Birindelli et al. (2020)
H. mormyrops	LBP 8103-37540	Rio Pomba	Paraíba do Sul	MT427917	Birindelli et al. (2020)
H. mormyrops	ZUEC 8198 - LGC 4965	Rio Mutum	Doce	RDOCE282-14	BOLD System
H. mormyrops	ZUEC 8198 - LGC 4966	Rio Mutum	Doce	RDOCE283-14	BOLD System
H. mormyrops	ZUEC 8198 - LGC 4967	Rio Mutum	Doce	RDOCE293-14	BOLD System
H. santanai	LBP 28094-96860	Rio Gongogi	Contas	MT427922	Birindelli et al. (2020)
H. santanai	LBP 28094-96862	Rio Gongogi	Contas	MT427924	Birindelli et al. (2020)
H. santanai	LBP 28094-96863	Rio Gongogi	Contas	MT427925	Birindelli et al. (2020)
H. santanai	LBP 28094-96861	Rio Gongogi	Contas	MT427923	Birindelli et al. (2020)

	PC 1	PC 2
Eigenvalue	5.928	2.712
% variance	32.937	15.069
Snout tip to dorsal-fin origin	0.32688	0.03479
Snout tip to adipose-fin origin	0.1436	0.20841
Snout tip to pelvic-fin origin	0.30981	-0.22224
Snout tip to anal-fin origin	0.26154	-0.33435
Dorsal-fin origin to caudal-fin origin	-0.21008	0.26634
Dorsal-fin origin to adipose-fin origin	-0.17341	0.3769
Caudal peduncle length	-0.13581	0.20942
Caudal peduncle depth	0.12707	-0.263
Body depth at dorsal-fin origin	0.065593	-0.31671
Body width at dorsal-fin origin	0.11333	-0.073941
Head length	0.27078	0.2994
Preopercle length	0.29943	0.24021
Snout length	0.17237	0.38642
Eye diameter	0.19135	-0.044524
Snout depth at anterior eye margin	0.24789	0.19482
Head depth at tip of supraoccipital	0.29568	0.0089302
Head width at opercle	0.32373	0.15197
Interorbital distance	0.31498	0.051129

	1	2	3	4	5	6	7	8	9	10	11
1. H. santanai (Contas)	0.0	1.0	1.1	1.2	1.2	1.4	1.0	1.0	1.0	1.3	1.3
2. H. mormyrops (Doce)	5.5	0.2	0.9	1.0	0.9	1.2	0.8	0.7	0.8	1.2	1.1
3. H. mormyrops (Paraiba do Sul)	6.7	5.4	0.0	0.8	1.0	1.1	0.8	0.8	1.0	1.2	1.2
4. H. copelandii (Doce)	6.6	5.4	3.6	0.0	0.7	0.8	1.0	1.0	1.1	0.9	0.9
5. H. copelandii (Paraiba do Sul)	7.4	5.5	4.7	3.6	0.1	0.8	1.1	1.0	1.1	0.9	0.9
6. H. thayeri (Doce)	8.1	7.2	6.3	3.7	3.4	n/c	1.3	1.2	1.2	0.6	0.6
7. H. cf. steindachneri (Pardo)	5.9	4.5	5.1	3.8	7.2	8.6	0.3	0.3	0.6	1.2	1.2
8. H. steindachneri (Jequitinhonha)	5.2	3.3	4.6	3.9	6.5	7.9	0.7	0.2	0.5	1.2	1.2
9. H. cf. steindachneri (Mucuri)	5.4	4.2	6.0	4.0	6.7	8.2	2.8	1.8	0.2	1.1	1.3
10. H. cf. steindachneri (Rio de Janeiro)	7.7	6.9	6.7	4.1	3.7	2.3	7.5	6.9	7.0	0.2	0.3
11. H. cf. steindachneri (Ribeira de Iguape)	8.0	7.0	6.0	4.2	3.0	2.1	8.0	7.0	8.0	1.0	0.1

	Holotype	Mean	Min-Max	SD
Standard length (mm)	323	185.6	79.37–357.8	–
Percentages in standard length
Snout tip to dorsal-fin origin	46	48.6	45.4–51	1.2
Snout tip to adipose-fin origin	*	84.1	82.3–86.8	1.1
Snout tip to pelvic-fin origin	50.4	52.4	48.3–56.8	1.8
Snout tip to anal-fin origin	*	80.3	77.5–84.7	1.6
Dorsal-fin origin to caudal-fin origin	*	51.3	47.6–56.9	1.7
Dorsal-fn origin to adipose-fin origin	38.9	37.6	34.7–43.4	1.6
Caudal peduncle length	11.2	10.3	7.2–12.5	1
Caudal peduncle depth	11.2	10.9	10.2–11.9	0.3
Body depth at dorsal-fin origin	32.1	28.9	26.9–32.5	1.4
Body width at dorsal-fin origin	*	15.3	12.3–18.2	1.6
Head length	21.5	23.4	20.4–26.4	1.3
Percentages in head length
Preopercle length	73.1	76.4	71.5–83.2	2.7
Snout length	40.3	39.8	33.4–52.8	2.9
Eye diameter	15.3	18.8	14.8–22.6	1.7
Snout depth at anterior eye margin	*	53.9	47.9–59.7	2.8
Head depth at tip of supraoccipital	93	82.6	73.4–91.5	4.2
Head width at opercle	*	57.6	49.1–63.6	3.8
Interorbital distance	46.9	41.5	35.9–47.4	2.6

	Holotype	Mean	Min-Max	SD
Standard length (mm)	273.4	162.4	90–315.9	–
Percentages in standard length
Snout tip to dorsal-fin origin	45.9	47.8	45.5–50.5	1.1
Snout tip to adipose-fin origin	83.4	84.4	82.2–86.7	0.9
Snout tip to pelvic-fin origin	49.5	49.7	46.6–53.3	1.3
Snout tip to anal-fin origin	76.9	77.1	72.4–83.7	1.8
Dorsal-fin origin to caudal-fin origin	51.8	53.4	48.8–56.9	1.6
Dorsal-fin origin to adipose-fin origin	38.9	39	36.2–41.4	1.1
Caudal peduncle length	11.7	11.4	9–13.4	0.9
Caudal peduncle depth	10.2	10.3	8.8–11.2	0.4
Body depth at dorsal-fin origin	27.8	27.8	25.3–31.8	1.4
Body width at dorsal-fin origin	15.7	15	12–17.8	1.3
Head length	21.7	23.7	20.8–25.7	0.9
Percentages in head length
Preopercle length	75.4	75.7	72.4–79.2	1.6
Snout length	41.2	40.5	36.9–53.6	2.3
Eye diameter	16.6	18.2	14.5–21.7	1.5
Snout depth at anterior eye margin	59.9	52.6	45.9–59.9	3
Head depth at tip of supraoccipital	87.3	80.4	73.8–93.3	3.4
Head width at opercle	60.5	54.9	48.1–64.3	3.5
Interorbital distance	41.5	39.3	35.1–47.3	2.1