Cordylancistrus santarosensis, Tan, Milton & Armbruster, Jonathan W., 2012

Tan, Milton & Armbruster, Jonathan W., 2012, Cordylancistrus santarosensis (Siluriformes: Loricariidae), a new species with unique snout deplatation from the Río Santa Rosa, Ecuador, Zootaxa 3243, pp. 52-58 : 53-56

Cordylancistrus santarosensis new species

Figs. 1 , 2 a

Holotype: MECN-DP 2061, 70.8 mm SL, Ecuador, El Oro Province, Pacific Ocean drainage, Río Santa Rosa, 13.5 km S of Santa Rosa on Hwy 92, -3.56944°, -79.94291°, W. Aguirre, 9 July 2008.

Paratypes: 5 specimens. All collections Ecuador, Río Santa Rosa. MECN-DP 2063, 1, 49.7 mm SL, Ecuador, El Oro Province, Pacific Ocean drainage, Río Santa Rosa, 13 km S of Santa Rosa on Hwy 92. -3.564139°, - 79.942306°, W. Aguirre, 9 July 2008. Remaining paratypes same locality data as holotype: MECN-DP 2062, 1, 24.3 mm SL; FMNH 120532, 1: 43.5 mm SL; AUM 52887, 2, 1 cleared and stained 43.9 mm SL, 1 specimen 44.3 mm SL.

Diagnosis. Cordylancistrus santarosensis can be distinguished from all other members of the Chaetostoma group by having plates at the end of the snout (except for a central region at the extreme anterior edge), but lacking plates laterally on the head (vs. either a fully plated snout or a naked snout) ( Fig 2 a). Cordylancistrus santarosensis can be distinguished from Co. platycephalus by the lack of keels on the lateral plates (vs. presence of keels on the lateral plates); from Co. platycephalus , Co. nephelion , and Chaetostoma (including Ch. platyrhyncha ) by the lack of a large papilla or papillae behind the dentary teeth (vs. dentary papilla present); from Co. daguae and Co. torbesensis by hypertrophied odontodes not reaching past the gill openings (vs. hypertrophied odontodes extending to or beyond pectoral-fin spine insertion); from Co. daguae and Co. nephelion by the lack of marked undulations in the lower lip (vs. lower lip with marked undulations); and from Ch. platyrhyncha by the presence of hypertrophied cheek odontodes reaching the gill opening (vs. cheek odontodes not well-developed); dorsal fin when adpressed not reaching the preadipose plates (vs. extending to or beyond preadipose plates); five anal-fin rays (vs. two to three anal-fin rays), and typically has 8 dorsal-fin rays (the holotype has 9 dorsal-fin rays) in Co. santarosensis (vs. usually 9–10 dorsal-fin rays in Ch. platyrhyncha ).

Description. Morphometric data are given in Table 1 . Largest specimen holotype, 70.8 mm SL. Body wide and depressed. Caudal peduncle compressed. Head wide and depressed, snout rounded. Body depth gently increases from the snout to the nares, angle of increase in body depth decreases between the nares and nuchal plate. Body depth gently decreases from nuchal plate to anteriormost dorsal procurrent caudal fin rays, then increases to caudal fin. Ventral surface flat.

Plates absent from anterior tip of snout. Naked snout tip followed by two columns of small plates (arrows, Fig. 2 a), and then narrow naked areas to evertible cheek plates; region posterior to snout tip fully plated medially. Lateral plates without keels. Mid-ventral plates bent at their midline above pectoral fin to form a weak ridge. Abdomen and ventral surface anterior to abdomen unplated. Five rows of plates on caudal peduncle. Median series 24 plates, mid-dorsal series 23–24 (mode 23) plates, mid-ventral series 23–26 (mode 24) plates. Exposed bones, plates and fin spines and rays covered in odontodes. Interopercular odontodes 16–31 (mode 19), holotype (31); number of odontodes greater with increased standard length, odontodes reaching to gill opening.

All fin spines and rays support odontodes. Dorsal fin II, 8–9 (mode 8); spinelet V -shaped, covered by skin, dorsal-fin spine lock functional. Nuchal plate variably exposed or hidden by predorsal plates. Dorsal spinelet covered by skin, and spinelet supporting odontodes in the holotype. Dorsal fin not reaching adipose fin when adpressed. Pectoral fins I, 6. Pectoral fin reaches to pelvic fin unbranched ray insertion when adpressed ventral to pelvic fin. Pelvic fins i, 5, lacking a fleshy crest, and not greatly widened. Anal fin i, 5. Caudal fin i, 14, i, obliquely truncate. Iris operculum present. Mouth wide with papillose lips, papillae of anterior lip larger. Dentary lacks large papillae behind teeth. Edge of posterior lip crenulate. Maxillary barbel base fused to posterior lip by a fleshy flap, barbel tip free. Jaws wide and jaw angle almost 180°. Teeth bicuspid with medial lobe longer than lateral lobe. Crown yellow, stalk white. Dentary teeth 48–77 (median = 57, N = 5). Premaxillary teeth 37–63 (median = 45, N = 5).

Color. Specimens preserved in 70% alcohol have a uniformly dark green base color with light markings. Light line originating from posterior edge of first mid-ventral plate and continuing dorsally to insertion of dorsal fin spine. Body with three dark saddles, divided by two pale bands; the first pale band is below the middle rays of the dorsal fin, and the second below and anterior to the adipose fin insertion. Two pale spots are present on the lateral, posterior end of the caudal peduncle, one dorsal and one ventral. Abdomen uniformly whitish.

Fins with alternating light and dark bands. Pectoral, pelvic, and dorsal fins with five dark bands, and caudal fin with six dark bands. Adipose fin usually with no bands, although two thin white bands were present in one specimen. Dark bands on fins formed from horizontally elongate spots centered on fin rays. There is no pigment on fin membranes of unpaired fins, and there is little pigment on fin membranes of paired fins. Light interspaces of lower lobe of caudal fin considerably darker than interspaces of upper caudal lobe.

Range. Known only from the type locality in the Río Santa Rosa (Gulf of Guayaquil drainage) near the southern coast of Ecuador ( Fig. 3).

Etymology. Named for the type locality, the Río Santa Rosa.

Figures

FIGURE 1. Cordylancistrus santarosensis, holotype, 70.8 mm SL, dorsal, lateral, and ventral views. Photos by M. Tan.

FIGURE 2. Dorsal view of left side of head of cleared-and-stained specimens, showing the difference in distribution of snout plates between a) Cordylancistrus santarosensis, AUM 52887, b) Chaetostoma platyrhyncha, ANSP 84570, c) Co. torbesensis, MCNG 8066, d) Ch. guariense, AUM 39880, and e) Ch. stanni, INHS 28838. Black line in a, d, and e represents the edge of the distribution of snout plates. The suspensorium has been removed from a, b, c, and e. Vertical bar represents 10 mm. Arrows point to where plates extend further towards the snout margin, between which there is a central region without plates at the extreme anterior edge of the snout (see Description). Photos by M. Tan.

Tables

TABLE 1. Morphometric data of Cordylancistrus santarosensis. Morphometric data are given as percentages of standard length.

SL	Holotype Avg 70.8 44.3	SD 43.5	Min 43.9	Max 49.7
Predorsal Length Head Length Head-dorsal Length	44.1 47.0 34.2 34.9 9.8 10.5	46.1 35.5 8.2	45.0 33.7 10.2	46.0 36.5 9.4
Head-eye Length Orbit Diameter Snout Length	12.8 13.4 5.4 6.2 21.3 20.5	12.8 6.0 21.5	13.6 6.9 19.5	14.0 5.6 21.4
Internares Width Interorbital Width Cleithral Width	4.2 4.7 14.7 18.0 30.3 30.7	4.6 18.0 30.8	4.1 17.8 29.3	3.9 16.2 31.9
Head-pectoral Length Thorax Length Pectoral-spine Length	32.1 30.3 24.4 21.8 26.5 26.8	30.4 23.4 25.7	31.2 21.6 25.4	31.7 25.0 28.4
Abdominal Length Pelvic Unbranched Ray Length Postanal Length	22.4 23.6 24.0 24.8 33.4 30.8	24.0 23.7 31.2	20.9 25.2 30.2	22.3 27.3 31.6
Anal-fin Unbranched Ray Length Head Depth Dorsal-pectoral Distance	9.0 8.2 24.5 24.5 28.2 28.2	12.5 24.4 27.7	8.5 25.0 28.7	9.0 24.4 28.8
Dorsal spine Length Dorsal-pelvic Distance Dorsal-fin base Length	20.1 22.8 19.6 21.6 25.1 25.1	20.6 22.0 24.9	22.0 22.7 24.2	22.7 19.0 23.1
Dorsal-adipose Distance Adipose-spine Length Adipose-upper caudal Distance	14.9 15.7 8.2 8.6 14.3 14.7	14.5 8.6 14.8	15.6 8.4 12.4	14.8 9.7 13.3
Caudal peduncle Depth Adipose-lower caudal Distance Adipose-anal Distance	9.5 11.1 21.8 21.0 17.4 19.7	11.3 22.6 18.4	12.4 18.4 17.7	9.5 21.8 16.6
Dorsal-anal Distance Pelvic-dorsal Distance Mouth Length	13.1 15.0 23.4 26.6 18.9 21.2	15.0 27.7 21.1	14.9 24.2 21.0	14.3 24.1 21.6
Mouth Width Barbel Length Dentary tooth cup Length	29.7 28.7 3.4 4.0 10.1 10.3	29.2 3.1 7.6	29.9 3.5 7.7	29.4 2.2 10.5
Premaxillary tooth cup Length	9.8 10.1	9.7	9.3	8.6