Rhinotocinclus acuen ( Silva, Roxo & Oliveira, 2014 ), 2022

Reis, Roberto E. & Lehmann A., Pablo, 2022, A new genus of armored catfish (Siluriformes: Loricariidae) from the Greater Amazon, with a review of the species and description of five new species, Neotropical Ichthyology (e 220002) 20 (2), pp. 1-100 : 83-86

Rhinotocinclus acuen ( Silva, Roxo & Oliveira, 2014) , new combination

( Fig. 44 ; Tab. 9 )

Hisonotus acuen Silva, Roxo & Oliveira, 2014:107 (Type-locality: Brazil, Mato Grosso State, municipality of Querência, affluent of rio Toguro, rio Xingu basin, 13°00’26”S 52°11’27”W. Holotype: MZUSP 115350).

Diagnosis. Rhinotocinclus acuen is distinguished from congeners, except R. chromodontus , R. jumaorum , and R. dinizae , by having the dominant color pattern formed by a dark stripe from the snout tip, through the eye and extending to end of caudal peduncle (Fig. 7E; vs. dominant color pattern formed by dark bars separated and distinct, or dark bars wide and partially coalesced or closed together), and by having a V-shaped light mark from the snout tip to each nostril (Figs. 6C,D; vs. light mark absent, Y-shaped or present as two separate lines from snout tip diverging to each nostril). It is also distinguished from congeners, except R. chromodontus , R. dinizae , R. hera , and R. jumaorum , by lacking an adipose fin or platelets at the adipose-fin position (vs. adipose fin or platelets present). Rhinotocinclus acuen is distinguished from R. chromodontus by having oral teeth light ochre (Fig. 5B; vs. teeth reddish brown), caudal fin with a dark blotch at the base and two irregular dark bands (vs. caudal fin mostly brown, with two hyaline spot on upper and lower lobes), the dorsal- and pectoral-fin spines with 2–3 dark dots (vs. spines homogeneously dusky), narrower body (cleithral width 21.7– 24.1% vs. 24.9–27.9% SL and 57.6–62.7% vs. 67.7–76.2% HL), and fewer teeth (17–22 premaxillary, 14–19 dentary; vs. 26–40 and 21–34, respectively). It is distinguished from R. jumaorum by having teeth light ochre (vs. teeth brown), and by the relative proportion of caudal peduncle depth and body width (caudal peduncle depth 39.2–45.0% vs. 35.4– 39.0% cleithral width). Rhinotocinclus acuen is distinguished from R. dinizae by having shorter fins (dorsal-fin spine 20.0–22.8% vs. 22.8–25.5% SL, anal-fin unbranched ray 15.0–17.4% vs. 18.5–19.5% SL, and pectoral-fin spine 23.1–26.9% vs. 28.1–30.0% SL), and a shorter head (head length 37.0–40.0% vs. 40.0–41.8% SL).

Geographical distribution. Rhinotocinclus acuen occurs in the tributaries of the upper rio Xingu in the state of Mato Grosso, Brazil ( Fig. 43 ).

Remarks. Rhinotocinclus acuen was also described as a member of Hisonotus , and accordingly compared to other species of the later genus ( Silva et al., 2014). Interestingly, in the diagnosis of the new species the authors begin saying “ Hisonotus acuen differs from all congeners except H. bockmanni , H. chromodontus , H. insperatus , H. luteofrenatus , H. oliveirai , and H. paresi by having a functional V-shaped spinelet”. Both H. bockmanni and H. chromodontus are herein being tranferred to Rhinotocinclus and the remaining species have already been transferred to Curculionichthys , the functional V-shaped spinelet indeed diagnosing R. acuen and, in fact, all Rhinotocinclus and Curculionichthys species, from Hisonotus . Extintion risk of Rhinotocinclus acuen is currently not assessed.

Material examined. Rio Xingu basin, Mato Grosso State, Brazil: MZUSP 115350 , holotype (measured), creek tributary to rio Toguro , Querência, 13°00’26”S 52°11’27”W . MCP 40543 , 22 (5 measured), AUM 73894, 10 , INPA 59665, 10 , ROM 111486, 10, córrego Trinta, tributary to rio Suaizinho on road BR-153 between Alô Brasil and Ribeirão Cascalheira, Ribeirão Cascalheira, 12°14’54”S 51°42’45”W. MCP 32671, 2, creek tributary to rio Azul on road MT-140, Santa Carmen, 11°59’55”S 55°16’39”W. MCP 32672, 5, rio Ferro on road from Novo Mato Grosso to Nova Ubiratã, ca. 25 km SW of Novo Mato Grosso, Nova Ubiratã, 13°03’32”S 55°02’12”W. MCP 32673, 10 (3 measured) + 2 cs, creek tributary to rio da Saudade on road MT-423, ca. 38 km SE of Marcelândia, Analândia do Norte, 11°13’23”S 54°17’24”W . MCP 32679, 2, córrego Tatu on road MT- 423, 14 km W of Cláudia, Cláudia, 11°28’36”S 54°58’47”W . MCP 32680, 1, córrego Saudade on road from Santa Helena to Marcelândia, 66 km SE of road BR-163, Marcelândia, 11°07’07”S 54°40’15”W. MCP 32681, 3, ribeirão Camparina on road MT-320 from Santa Helena to Marcelândia, 79 km SE of road BR-163, Marcelândia, 11°06’27”S 54°33’03”W . MCP 32682, 9, rio Azul on road MT-140, ca. 7 km NNW of Santa Carmen, Santa Carmen, 11°54’42”S 55°17’48”W . MCP 32683, 3, creek on road from Santa Terezinha to Iberê, ca. 10 km W of Iberê, Nova Ubiratã, 12°45’19”S 54°34’25”W . MCP 32684, 7 + 1 cs, creek tributary to rio Tartaruga on road from Vera to Feliz, Vera, 12°15’55”S 55°15’37”W . MCP 32685, 3, rio Azul on road MT- 423, 16 km w of Cláudia, Cláudia, 11°28’20”S 54°59’40”W . MCP 32686, 6, rio Tartaruga on road MT-423 ca. 20 km E of Vera, Cláudia, 11°30’36”S 54°42’43”W. MCP 32687, 16, creek on road from Novo Mato Grosso to Nova Ubiratã, 7 km SW of Novo Mato Grosso, Nova Ubiratã, 12°57’10”S 54°54’46”W . MCP 32688, 3, rio Tartaruga at Nova Ubiratã, Nova Ubiratã, 13°02’03”S 55°16’07”W. MCP 32689, 1, creek on road MT-320 from Santa Helena to Marcelândia, 73 km SE of road BR-163, Marcelândia, 11°07’39”S 54°36’52”W . MCP 32690, 6, rio da Saudade on road MT- 423, 31 km SE of Marcelândia, Marcelândia, 11°11’11”S 54°19’27”W . MCP 32691, 2, creek on road MT- 423, 22 km SE of Marcelândia, Marcelândia, 11°12’21”S 54°23’19”W. MCP 32692, 4, creek tributary to rio Tartaruga on road from Novo Mato Grosso to Nova Ubiratã, ca. 44 km WSW of Novo Mato Grosso, Nova Ubiratã, 13°02’43”S 55°12’21”W. MCP 32693, 2, rio Von der Steinen (or Atelchu) on road from Santa Terezinha to Iberê, ca. 28 km W of Iberê, Nova Ubiratã, 12°47’05”S 54°40’49”W. MCP 32694, 6, creek tributary to rio Manissamá-Miçu on road MT-423 ca. 11.6 km SE of Marcelândia, Marcelândia, 11°09’46”S 54°27’01”W. MCP 32695, 2, rio Tartaruga on road from Vera to Feliz Natal, 20 km NE of Vera, Vera, 12°14’21”S 55°07’11”W. MCP 32696, 4, creek ca. 2 km N of Novo Mato Grosso, Nova Ubiratã, 12°53’49”S 54°50’54”W . MCP 40283, 45 , MHNG 2787.080, 10, rio Traíras ca. 3 km W of Posto da Mata on road BR 242, Posto da Mata, 11°42’40”S 51°39’18”W . MCP 40299, 12, córrego da Caaporã, tributary to córrego Três Marias, rio Suiazinho on road BR-158, Ribeirão Cascalheira, 12°32’10”S 51°46’45”W . MCP 40365, 16 (2 measured), creek N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°35’50”S 51°46’55”W . MCP 40402, 23, creek tribuatry to rio Suiazinho on road BR-158, ca. 1 km N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°29’21”S 51°46’06”W . MCP 40720, 10, creek tributary to rio Suiazinho on road BR 158, ca. 1 km N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°29’21”S 51°46’06”W . MCP 40732, 18, córrego Trinta, tributary to rio Suaizinho on road BR-153 between Alô Brasil and Ribeirão Cascalheira, Ribeirão Cascalheira, 12°14’54”S 51°42’45”W . MCP 40790, 5, creek N of Ribeirão Cascalheira, Ribeirão Cascalheira, 12°35’50”S 51°46’55”W. MCP 40814, 5, rio Traíras ca. 3 km W of Posto da Mata on road BR-242, Posto da Mata, 11°42’40”S 51°39’18”W.

Figures

FIGURE 43 | Geographic distribution of Rhinotocinclus species of the R. chromodontus group in southern Amazon. Rhinotocinclus acuen (red dots); R. chromodontus (blue dots); R. dinizae (cyan dots); R. jumaorum (yellow dots). T = Type-locality.

FIGURE 44 | Rhinotocinclus acuen, MCP 40543, 27.4 mm SL, female, córrego Trinta, tributary to rio Suaizinho on road BR-153 between Alô Brasil and Ribeirão Cascalheira, Ribeirão Cascalheira, Mato Grosso, Brazil.

Tables

TABLE 9 | Descriptive morphometrics of Rhinotocinclus species. Values given as percent of standard length or head length. Range includes the holotype (Hol), SD = standard deviation.

	R. chromodontus n = 11						R. acuen n = 11					R. jumaorum n = 14				R. dinizae n = 4
Character
	Hol	Low	High	Mean	SD	Hol	Low	High	Mean	SD	Hol	Low	High	Mean	SD	Low	High	Mean	SD
Standard length (mm)	26.2	23.3	32.2	26.9		25.8	22.3	27.4	25.2		26.3	24.4	31.0	27.0		17.8	20.0	19.0
Percent of SL
Body depth	17.9	17.0	18.9	17.9	0.61	19.7	16.6	19.7	17.7	1.00	15.2	14.7	17.9	16.1	0.96	15.8	16.8	16.4	0.47
Predosal distance	47.3	47.0	51.4	48.6	1.32	50.1	47.5	50.1	48.8	0.78	48.1	47.8	50.9	49.1	1.11	46.9	49.5	48.5	1.13
Prepelvic distance	41.6	40.9	45.3	43.2	1.59	44.1	42.9	46.5	44.1	1.08	44.3	42.0	45.2	43.9	0.82	44.9	46.6	45.7	0.82
Preanal distance	61.8	61.8	66.4	64.2	1.35	63.8	62.4	65.2	63.8	1.12	65.7	62.7	65.7	64.1	0.87	63.6	65.5	64.3	0.84
Preadipose distance	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-
Dorsal-fin spine length	22.1	18.5	23.2	20.8	1.60	20.0	20.0	22.8	21.3	0.94	21.7	20.4	23.9	21.8	0.87	22.8	25.5	24.1	1.28
Anal-fin unbranched ray length	16.0	13.5	17.0	15.1	0.97	15.4	15.0	17.4	16.3	0.83	16.5	15.3	18.2	16.8	0.67	18.5	19.5	19.0	0.44
Adipose-fin spine length	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-
Pectoral-fin spine length	26.8	26.7	29.5	27.8	0.88	24.9	23.1	26.9	24.7	0.98	25.1	23.3	26.7	24.8	1.01	28.1	30.0	29.1	0.83
Caudal peduncle depth	9.5	8.9	9.8	9.4	0.27	9.7	8.5	10.5	9.5	0.54	8.6	8.4	9.5	8.9	0.34	8.9	9.5	9.1	0.27
Dorsal-adipose fin distance	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-
Dorsal-fin base length	-	10.6	14.2	12.4	1.03	-	11.6	13.5	12.6	0.59	10.8	9.6	11.1	10.4	0.39	11.0	12.8	12.0	0.88
Lower caudal-fin principal ray	27.2	23.2	28.4	25.1	1.85	-	22.7	27.3	25.7	1.34	-	22.8	28.4	25.4	1.93	27.1	29.7	28.1	1.14
Cleithral width	25.2	24.9	27.9	26.5	1.03	24.1	21.7	24.1	22.9	0.71	24.4	22.4	24.9	23.8	0.75	22.5	23.8	23.0	0.56
Head length	36.3	36.2	38.5	37.1	0.74	40.0	37.0	40.0	38.6	0.89	36.8	36.4	39.7	37.8	1.18	40.0	41.8	41.0	0.75
Percent of HL
Head depth	45.4	40.8	50.1	46.8	2.88	45.1	41.2	45.1	42.8	1.27	41.3	38.5	43.6	41.2	1.70	37.8	42.4	39.7	2.11
Interorbital distance	37.1	33.9	37.4	36.1	1.05	35.2	34.9	38.7	36.0	1.09	35.6	32.1	37.9	35.1	1.98	33.8	36.2	35.0	1.08
Orbital horizontal diameter	13.1	11.5	13.7	12.8	0.63	14.0	13.0	15.5	13.9	0.73	14.0	12.8	15.0	13.9	0.67	12.9	14.8	13.8	0.78
Snout length	55.4	53.4	57.4	55.2	1.23	53.0	53.0	56.1	55.0	1.16	57.7	55.5	59.8	57.4	1.12	52.9	54.3	53.7	0.62
Internarial distance	8.8	6.2	13.1	8.8	2.19	9.8	8.2	9.9	9.2	0.54	11.6	9.9	13.7	11.5	0.96	7.3	11.3	10.1	1.88
Tooth count
Premaxilla	29	26.0	40.0	31.6	5.01	22	17	22	20.1	1.70	28	20.0	33.0	27.4	3.67	16.0	17.0	16.3	0.50
Dentary	25	21.0	34.0	26.8	3.74	18	14	19	16.5	1.75	25	18.0	28.0	23.3	3.02	12.0	14.0	13.3	0.96